TECHNICAL REPORT S-72-12

IN SITU TESTS FOR THE DETERMINATION OF ROCK MASS SHEAR STRENGTH

by

T. W. Zeigler

November I972 TA 7 Sponsored by Office, Chief of Engineers, U. S. Army .W 34t S-7 2-1 2 Conducted by U. S. Army Engineer Waterways Experiment Station 1972 Soils and Pavements Laboratory Vicksburg, Mississippi

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

Ä * « %M • ¿ i s I LIBRARY

FE B 2 3 1973

Bureau of Reclamation Denver, Colorado

Destroy this report when no longer needed. Do not return it to the originator.

The findings in this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.

k. BUREAU OF RECLAMATION DEI 92021814

IN SITU TESTS FOR THE DETERMINATION OF ROCK MASS SHEAR STRENGTH

by

T. W. Zeigler

JOI ioiu u u lOlIffiDD]IDI

November 1972

Sponsored by Office, Chief of Engineers, U. S. Army Engineering Study 553

Conducted by U. S. Army Engineer Waterways Experiment Station Soils and Pavements Laboratory Vicksburg, Mississippi

ARMY-MRC VICKSBURG, MISS.

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED /

FOREWORD

This study was conducted by the U. S. Army Engineer Waterways Experi­ ment Station (WES). The work was sponsored by the Office, Chief of Engi­ neers (OCE), under Engineering Study (ES) 553. The study was conducted intermittently during the period from July 1969 to July 1971. Mr. T. W. Zeigler conducted the research under the general supervision of Messrs. W. C. Sherman, Chief, Soil and Rock Mechanics Branch, and D. C. Banks, Chief, Rock Mechanics Section. Messrs. J. P. Sale and R. G. Ahlvin were Chief and Assistant Chief, respectively, of the Soils and Pavements Laboratory during the period of investigation. This report was prepared by Mr. Zeigler. COL Levi A. Brown, CE, and COL Ernest D. Peixotto, CE, were Directors of WES during preparation of this report. Mr. F. R. Brown was Technical Director.

iii CONTENTS

Page

FOREWORD ...... , ...... iii CONVERSION FACTORS, BRITISH TO METRIC UNITS OF MEASUREMENT...... vii SUMMARY ...... ix PART I: IN TRODUCTION...... 1 Purpose of R e p o r t...... 1 S c o p e ...... 1 PART II: METHODS OF DETERMINING IN SITU SHEAR S T R E N G T H ...... 3 Direct Shear T e s t ...... 3 Triaxial T e s t ...... 7 Torsion Shear T e s t ...... 9 Pull-Out Shear Test ...... 13 PART III: DIRECT SHEAR T E S T ...... 15 Shear of Discontinuities ...... 15 Shear of Intact Rock Including Hard Clays and Weak Shales . . . 54 Shear of Concrete Blocks on Rock Surfaces ...... 68 PART IV: INTERPRETATION OF IN SITU DIRECT SHEAR TEST RESULTS . . . 79 Introduction...... 79 Failure Criteria ...... 79 Failure Envelopes...... 84 Data from Displacement Observations ...... 89 Reliability of Test Results...... 92 Application of Test Results...... 94 Summary of Shear S t r e n g t h s ...... 101 PART V: CONCLUSIONS AND RECOMMENDATIONS...... 107 LITERATURE C I T E D ...... Ill SELECTED BIBLIOGRAPHY...... 117 TABLES 1-4 APPENDIX A: CASE HISTORIES INVOLVING TESTS OF CLEAN DISCONTINUITIES APPENDIX B: CASE HISTORIES INVOLVING TESTS OF FILLED DISCONTINUITIES APPENDIX C: CASE HISTORIES INVOLVING TESTS OF INTACT MATERIAL APPENDIX D: CASE HISTORIES INVOLVING TESTS OF CONCRETE BLOCKS CAST ON ROCK SURFACES APPENDIX E: CASE HISTORIES INVOLVING TESTS OF VARIOUS CONDITIONS

v CONVERSION FACTORS, BRITISH TO METRIC UNITS OF MEASUREMENT

British units of measurement used in this report can be converted to metric units as follows:

Multiple By To Obtain inches 2.54 centimeters feet 0.3048 meters square inches 6.4516 square centimeters square feet 0.092903 square meters pounds 0.45359237 kilograms tons (2000 lb) 907.185 kilograms pounds per square inch 0.070307 kilograms per square centimeter pounds per square foot 4.88243 kilograms per square meter pounds per cubic foot 16.0185 kilograms per cubic imeter

vii SUMMARY

Rock shear strength is often determined from in situ tests. Many cases have been reported in the literature describing in situ shear test procedures and test results. The purpose of this report is to summarize this information for guidance in planning and evaluating such tests. The types of tests discussed are: (1) direct shear test, (2) triaxial or multiaxial test, (3) torsion shear test, and (4) pull-out test. The direct shear test is most widely used, and some 48 case histories of such tests are summarized in Appendixes A through E. The main advantage of the direct shear test is the ability to measure the shear resistance in any desired direction along potentially critical discontinuities. The test is also popular due to its adaptability to field conditions; tests can be conducted in trenches, adits, tunnels, and even calyx drill holes. Direct shear tests have been carried out on clean and filled discon­ tinuities, intact materials, and concrete-on-rock contacts. Specimen size, types of encasements (when used), loading procedures, and test moisture conditions are varied. Instrumentation is generally provided for measuring horizontal and vertical displacements. Illustrations of various direct shear test setups that have been employed are presented. Failure envelopes determined from in situ direct shear test results reported in the literature were generally straight lines defined by Mohr- Coulomb shear strength parameters 0 and c . Average peak strength para­ meters are given below:

______Test Zone______Average 0, deg Average c, psi Clean discontinuities 39 24 Filled discontinuities 30 23 Intact rock 50 70 Concrete-on-rock contacts 38 40

As expected, intact specimens exhibited the greatest average shear strength, and filled discontinuities the least.

ix IN SITU TESTS FOR THE DETERMINATION OF ROCK MASS SHEAR STRENGTH

PART I: INTRODUCTION

Purpose of Report

1. A reliable assessment of the shear strength of rock masses is often required to ensure a safe and economical design of many civil engi­ neering projects. In most cases the rock mass contains joints, bedding planes, shear zones, faults, and foliation surfaces. Since the shear strength of a rock mass is usually governed by the number, location, orientation, and physical properties of these geological discontinuities, it is often quite difficult to determine the shear strength accurately. 2. A preferred method of determining the shear strength is by testing relatively large samples in the field. Many cases have been reported in the literature describing in situ shear test procedures and test results. The purpose of this report is to summarize this information for guidance in planning and evaluating such tests.

Scope

3. The report discussed methods of conducting various in situ field tests, such as the direct shear tests, the triaxial or multiaxial test, and the torsion shear test. Most of the discussion pertains to the direct shear test since it was found to be the one most often used for field testing. The shear mechanism, test procedures, and data interpretation are discussed for direct shear tests on clean and filled discontinuities, intact material, and concrete-on-rock contacts. Strengths determined from in situ direct shear tests reported in the literature are summarized. The information contained in this report came from a review of case histories on field direct shear testing (see Appendixes A to E) and discussions of rock mass shear strength in the literature.

2 PART II: METHODS OF DETERMINING IN SITU SHEAR STRENGTH

Direct Shear Test

Description 4. By far the most common in situ test used for the determination of shear strength is the direct shear test. Clean and filled discontinuities, intact material, and concrete-on-rock contacts are often tested in direct shear. The selection of critical zones for testing should be preceded by a detailed engineering geology investigation of the project site. The purpose and methods of engineering geology investigations related to shear strength are discussed by Clar et al. (1964), Duncan (1965), Deere et al. (1967), Mizukoshi et al. (1967), Muller and John (1963), Rocha (1964a), and Serafim and Guerriero (1966). In situ shear tests in rock conducted from 1934 through 1965 are discussed by Link (1969). Recommended field direct shear test procedures were presented to the American Society for Testing and Materials (ASTM) as part of an effort to establish an ASTM standard for measuring the in situ shear strength of rock (Dodds, 1970). 5. In the simplest form of the direct shear test, the specimen to be sheared is subjected to a load perpendicular to and another load parallel to a predetermined failure plane or failure zone; these loads are termed the normal load N and shear load S , respectively, as shown in figs, la, lb, and lc. The normal and shear stresses are assumed to be distributed uniformly over the test surface and are computed by dividing the respective loads by the test surface area. The normal force is applied first and is generally held constant until the specimen fails under an increasing shear force. The normal and shear loads are usually applied by hydraulic jacks. The only exceptions are cases where the normal load is produced solely by the weight of the test block. Consolidation time, rate of loading, and moisture conditions can be varied. The essential features of the direct shear test are presented in Part III.

3 NORMAL LOAD N

a. TEST OF DISCONTINUITY

NORMAL LOAD N

b. TEST OF INTACT ROCK

NORMAL LOAD N

c. TEST OF CONCRETE BLOCK CAST ON ROCK

Fig. 1. In situ direct shear test 4 Advantages and disadvantages 6. The popularity of the direct shear test is mainly due to its adaptability to field conditions. The test can be conducted in a trench, an underground adit, or a tunnel, and in at least one case at the bottom of a calyx drill hole as illustrated in fig. 2 (Case History B-4)*. 7. The direct shear test is ideal for determining discontinuity shear strength since the failure plane location and direction of failure are chosen before testing (John, 1962). This ability to orient the shear force in any desired direction is considered essential since rock shear strength is highly anisotropic. 8. A volume increase in the failure zone caused by the overriding of irregularities usually accompanies shear failure along a discontinuity (Deere et al., 1967). The direct shear test can allow free movement per­ pendicular to the failure plane; therefore, any volume increase in the failure zone can be detected. 9. Although the direct shear test does have a number of advantages making it suitable for measuring rock shear strength in situ, not all engineers favor the direct shear test. Rocha (1964b) and Salas and Uriel (1964) point out that the normal stress distribution can be nonuniform due to the bending moment induced by the shear load. When testing intact speci­ mens, the normal stress can actually become tensile near the side of the block to which the shear load is applied. Tensile cracks could occur with­ in the failure zone, which would ultimately reduce the measured shear strength. When testing discontinuities, the normal stress could not become tensile unless the discontinuity surfaces were cemented or welded together; however, the stress could conceivably become zero. 10. Lane (1964) and Rocha (1964b) both emphasize that the direct shear test can only measure the shear strength along a particular joint or

* Case history numbers refer to similarly numbered items in the appendixes

5 SECTION A-A

PLAN 10 1 2 FEET

Fig. 2 . Arrangement of in situ shear test in a calyx hole at Meadowbank Dam (Maddox et al., 1967a)

6 other discontinuity. The shear strength of the entire jointed rock mass must be determined by some other means. This may well be true, since for a direct shear test to yield results which represent the entire rock mass, the zone failed must represent the zone or surface along which failure would likely occur within the rock mass. The failure surface path is dependent on the stress distribution as well as the number, orientation, and physical properties of the joints and as shown by Jaeger (1960) and Maurer (1965), the failure path may be along the joints or it can inter­ sect intact materials between joints.

Triaxial Test

11. Some engineers would prefer to use the triaxial compression test rather than the direct shear test for field testing. The selection of test type is of course dependent on the type of problem being investigated. In a randomly jointed rock mass, the failure surface location may be diffi­ cult to determine; therefore, an in situ triaxial test may be desirable for measuring rock mass shear strength. If a representative volume of the rock mass were tested, the failure surface would be allowed to follow the weakest path, whether it be along the discontinuities or through the intact rock. 12. Literature related to in situ triaxial testing is sparse. Cylindrical specimens were triaxially tested at the Punt Dal Gall Dam (Gilg and Dietlicher, 1965; Link, 1969) and block-type specimens were tested at the Kurobe IV Dam (John, 1961; Nose, 1964). At Kurobe IV granite specimens of 9.3 by 4.7 by 9.3 ft* were formed within a test adit and were loaded as shown in fig. 3. The base (9.3 by 4.7 ft) was left attached to the floor of the adit and one side (9.3 by 4.7 ft) was left attached to the wall of the adit. Continued interest in methods for testing of rock in situ will likely generate more triaxial testing in the future.

* A table of factors for converting British units of measurement to metric units is presented on page vii.

7 a) BLOCK I WITH PRINCIPAL LOADING DEVICES

Fig. 3- In situ triaxial compression tests on rock (John, 1962)

8 Torsion Shear Test

13. A torsion shear test was developed by Terrametrics Inc. and used at the Muddy Run Embankment Project (Wilson and Marano, 1968) and more recently at the Hannibal Dam Project. This test can measure either intact or joint strength. The test apparatus and procedure are described by Hartmann (1966). General test procedures and some details of the tests at Muddy Run Embankment and Hannibal Dam site are given below. 14. Five feet of NX-size hole followed by five feet of BX-size hole are first drilled to make up the inner hole shown in fig. 4. A 12-in. or larger overcoring bit is then used to isolate and form the specimen*s outer wall (see fig. 4). Discontinuities that are to be tested must be oriented perpendicular to the initial drill hole and located above the bottom of the overcore hole. 15. The normal load is applied by tensioning an anchor or rock bolt to the bottom of the inner drill hole. The normal load can be held con­ stant throughout the test and is measured by a load cell as shown in fig. 4. Three tests, each at a different normal load, are usually performed. 16. A steel torque tube is placed in the overcore slot and cemented to the outside wall of the specimen. A torque arm is then locked into the torque tube, and torque applied by two hydraulic rams on a common pressure line (see fig. 4). The torque reaction is obtained by an anchor grouted in the rock a few feet from the test section. Dynamometers were used at Hannibal Dam to measure the load applied to the ends of the torque arm. 17. Circumferential movements are measured during each test. At Hannibal Dam extensometers were fastened to the rock anchors and movement sensing wires were connected to the steel torque tube. All loads and movement measurements were fed into a central switching box. 18. At Muddy Run Embankment (Wilson and Marano, 1968), the torque was applied in equal increments. Readings of torque, normal stress, and circumferential movement were taken until the normal stress remained con­ stant over a five-minute period under each load increment. No mention was

9 & \ ; •------GROU T

Pj*------ROCK BOLT ANCHOR

b. SECTIONAL VIEW OF TEST EQUIPMENT

Fig. if. Torsion shear test setup (Hartmann, 1966)

10 made of moisture conditions; however, Hartmann (1966) states that saturated conditions can be used if desired. 19. The data obtained from the tests on severely weathered schist at Muddy Run Embankment are shown in fig. 5. In fig. 5a are plots of shear and normal stress versus circumferential movement. Normal stress versus torsion shear stress at failure are plotted in fig. 5b. At failure, the maximum shear stress was assumed to be developed over the entire failure surface. The maximum shear stress can be computed from the maxi­ mum torque:

T (i) O where

T = shear stress o T = torque measured

d = diameter of specimen 20. Wilson and Marano (1968) suggest that for hard intact rock, failure be assumed to occur when the shear strength at the circumference of the test specimen is reached. Shear stress at failure would be deter­ mined by: 16T (2) TTC

21. The torsion shear test does have some advantages. The torsion test requires minimal excavation and subjects the specimen to minimal exposure to the atmosphere. The torsion test was found to be acceptable for in situ testing of weak silty clay seams contained in the soft clay shale at the Hannibal Dam site.* The test can also be used in more compe­ tent rock. In fact a number of intact specimens can be tested in the same

* Information from a letter dated 27 Oct 71 from Edwin W. Thomas, Assist­ ant Chief, Engineering Division, Pittsburgh District, U. S. Army Corps of Engineers, to the Director, U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.

11 est wahrd c s a Mdy u Embankment Muddy Run at ist sch weathered f o ts s te ig. F

5 TORSION SHEAR STRESS AT FAILURE, PSI STRESS, PSI Ts rs t otie fo trin shear torsion from obtained lts resu Test . . EAINHP EWE NRA AND NORMAL BETWEEN RELATIONSHIP b. 2 4 6 8 10 120 100 80 60 40 20 0 g

\ VERSUS STRESS SHEAR AND NORMAL . \ \ X Wlo ad aao 1968) Marano, and (Wilson \ HA TESA FAILURE AT STRESS SHEAR

_____\ / ROTATIONAL MOVEMENT ROTATIONAL y y OML TES T ALR, PSI FAILURE, AT STRESS NORMAL •

•

_____

0 >

\

\

12 \

\ \ • Sfa. 23+00, depth 12 feet feet 12 depth 23+00, Sfa. • X

r\

t. 2+7, et 8 feet 8 depth + 75, 22 Sta. \ \

LEGEND \

• \

hole simply by repeating the overcoring operation and using a longer torque tube. When testing discontinuities, the same failure surface can be re­ peatedly tested to obtain an estimate of the residual shear strength. 22. The main difficulty with the torsion shear test is its inter­ pretation. The movement of the specimen is circular, which causes stresses and deformations to vary within the failure zone along the diameter of the cylinder. When testing a joint, circular movement also prevents the measurement of shear resistance in specific directions. This is a serious disadvantage since shear strengths along discontinuities are highly anisotropic. Further study is needed in the interpretation of torsion shear tests. Comparison of results from torsion shear and more conven­ tional test methods such as direct shear would aid in determining the torsion test!s applicability.

Pull-Out Shear Test

23. Where large-scale shear tests may damage the foundation, the Multipurpose Dam Rock Testing Group, Japan, have utilized what they term the pull-out test (Construction Ministry of the Japanese Government, 1964; and Multipurpose Dam Rock Testing Group, 1964). These type tests have been conducted as part of the foundation investigation at Kawamata Dam. Steel bars, each consisting of forty-eight 0.2-in.-diam steel wires, were anchored with mortar inside a 2- to 4-ft-deep borehole having a diameter of 4 in. The steel bars were then pulled out with a jack reacting against a steel I-beam. Strains were measured with Carlson-type strain meters embedded 10 cm below the steel bars. 24. The force required to pull the anchor out of the borehole is considered the breaking load. The breaking load is divided by the side surface area to obtain the shear strength under tensile stress. The actual shear strength is believed to be larger than the tensile shear strength.

13 25. The pull-out test appears to give only an index of the rock mass shear strength. When the test is successful, a volume of material is ripped out of the mass, likely leaving most any shape of hole. It is difficult to determine if tensile strength, shear strength, or a combina­ tion of strengths are being measured. There is also no way that this test can measure shear strength along a discontinuity.

14 PART III: DIRECT SHEAR TEST

Shear of Discontinuities

26. The term "discontinuity" applies to many naturally occurring planes or near planar surfaces or zones of weakness, as well as fractures induced during excavation caused by blasting and stress relief. Relatively clean discontinuities include many joints, fractures, bedding planes, and foliation surfaces. Discontinuities may be open, closed, or healed (i.e., the joint surfaces are wholly or partially welded together). 27. The discontinuities chosen for in situ testing may contain clay or some type of crushed or sheared material. The fill material is usually produced by shearing and weathering along the discontinuity or deposited by groundwater flow. Clay-filled joints and seams, as well as other altered or sheared zones along joints, beds, and foliation surfaces, are often critically located, requiring that the resistance to sliding along these geological features be adequate. Similar to filled discontinuities are thin layers of weak material interbedded with hard intact rock. For example, weak shale beds are often interbedded with sandstone and limestone. 28. The usual method of measuring discontinuity shear strength is by forming a test block resting on the discontinuity and measuring its resist­ ance to sliding under a normal and shear force applied as shown in fig. la. In a few cases studied, the test blocks contained a number of randomly oriented discontinuities and shear occurred along interconnecting discon­ tinuity surfaces. 29. Data from tests of discontinuities are given in table 1 (clean discontinuities) and table 2 (filled discontinuities). A more detailed summary of test procedures and results is contained in the case histories found in the appendixes referred in the tables.

15 Shear mechanism 30. The development of testing techniques and interpretation of results are based on the assumed shear mechanism. For example, identical test data can lean to different values of shear strength, dependent upon the interpreter's concept of shear failure. A review of rock shearing behavior is therefore necessary before presenting the details of in situ shear tests. 31. Clean discontinuities. Naturally occurring discontinuities exhibit surface irregularities which contribute added shearing resistance. Patton (1966a, 1966b) ran direct shear tests on plaster-of-paris specimens to determine the mechanism of shear along an irregular rock surface. Speci­ mens were cast with irregular surfaces (teeth) inclined at the angle i measured with respect to the shear direction as shown in fig. 6. Both maximum and residual shear strength envelopes were constructed from test results. The maximum shear strength is denoted by the peak of the shear load versus displacement plot shown in fig. 7. The maximum strength envelopes were actually curves, but were approximated by two straight lines. Line OAB in fig. 6 is a typical maximum strength envelope (Deere et al., 1967). 32. Shear failure at low normal loads (line OA, fig. 6) is associated with vertical displacements produced by the upper block sliding up the inclined surfaces. Line OA is defined by S = N tan (0^ + i) where 0^ is the angle of sliding resistance along a prepared, macroscopically smooth, plaster surface. Similarly, the irregularities along naturally occurring discontinuities will exhibit an effective i-angle that can be determined from field observation or in situ direct shear test results. At high normal loads, the failure mode changes; the vertical displacements are small with the teeth sheared off near their base. Line AB is the failure envelope obtained from tests run at high normal loads and is in­ clined at the angle of residual shear strength 0^. 33. By continuing displacement beyond the peak shear strength, the residual shear strength is reached as shown in fig. 7. Line OC of fig. 6 is a typical residual shear strength envelope and is defined by

16 SHEAR STRENGTH, F Fig. Fig. ipaeet lusr i h maximum the and g tin stra illu displacement ig. ig. 6 7 Fiue neoe fr utpe inclined multiple for envelopes Failure . Po o ser od ess horizontal versus load shear of Plot . ufcs Dee t 1967) , . l a et (Deere surfaces eiul ha strength shear residual 17

S = N tan 0 . The angle of residual shear strength 0 was determined to r r be essentially equal to 0 (Patton, 1966a). The vertical distance be­ tween line OAB and OC represents the shearing resistance lost with dis­ placement and contributed by the irregularities as shown in fig. 6. A review of published rock shear test results has shown the shear behavior exhibited by the plaster-of-paris specimens to be analogous to that of rock (Patton, 1966a). 34. From the above concepts, the planarity of the discontinuities and the widely varying characteristics of the irregularities are seen to cause the shear strength along a discontinuity to be highly anisotropic. For example, a bedding surface having current ripple marks, as shown in fig. 8, will likely exhibit different shear strengths, s^, s^, s^, for each direction tested. 35. Shear failure along a discontinuity within a rock mass is often accomplished through progressive failure by which the maximum shear strength is not mobilized along the entire failure surface at one time (Deere et al., 1967). Progressive failure ultimately reduces the shear strength along the failure surface to a residual shear strength. The pro­ cess begins with a slight movement along the failure surface causing the stress to be withstood by steep irregularities. When these fail, the stresses are redistributed to the next steepest irregularities, which also may fail. This process continues until only very flat irregularities, which offer a minimal shear strength, are left to withstand the shearing stresses. Unless the remaining strength is sufficient, total failure will occur. This reduction in shear strength caused by the flattening of the irregularities along a discontinuity is illustrated by the typical Mohr failure envelopes shown in fig. 9. 36. Filled discontinuities. The shear mechanism active along filled discontinuities has not been directly studied; however, some insight can be gained from direct shear tests performed on irregular joints cast in a plaster-of-paris/celite mix and containing varying amounts of finely crushed mica (Goodman, 1969). The specimens shown in fig. 10a were 2.5 in.

18 Fig. 8. Rock surface showing how shear strength can vary with orientation (Deere et al., 1967)

Fig. 9* Failure envelopes expected for discontinuities (Deere et a l ., 19^7)

19 HORIZONTAL DISPLACEMENT, CM NORMAL DISPLACEMENT, CM 0.1 0.2 0.3 0.4 0.5 0.6

->2.50" .

Q. SPECIMEN

ho LEGEND SHEAR FORCE, KG O

• 1,3: PLASTER OF PARIS SHEAR TESTS O- ■O VI, VII, VIII: MICA SHEAR TESTS x- ■X 1- SHEAR TESTS ON JOINT BLOCKS 1,2: NO FILLING 3,4: .06" FILLING 5,6,9: .12" FILLING 7,8: .20" FILLING

NOTE: NORMAL FORCE ON SAMPLE WAS 530 LB IN A LL CASES.

b. SHEAR FORCE VERSUS C. SHEAR FORCE VERSUS HORIZONTAL DISPLACEMENT VERTICAL DISPLACEMENT

Fig. 1 0 . Load-deformation curves for direct shear tests on mica-filled joints (Goodman, 1969) in diameter with 4-1/2 teeth having an amplitude of 0.16 in., wave length of 0.56 in., and each inclined at 30 deg. For comparison, tests were con­ ducted on intact plaster blocks, crushed mica, unfilled joints, and joints filled with mica to a thickness of 0.06, 0.12, and 0.20 in. The filling thickness was measured perpendicular to the mean plane of the joint. 37. The test results are summarized in figs. 10 and 11. Typical shear force versus horizontal and vertical displacement plots are shown in 10b and 10c, respectively. Clean joints and those containing only 0.06 in. of fill exhibit shear stress versus horizontal displacement curves which rise steeply to a peak stress. During shear, the joint exhibits slight closure following by opening. As the filling thickness increases, the shear stress versus horizontal displacement curves become flatter and shearing is accompanied by only joint closures. Similar joint opening and closing was observed by Coulson (1970) during laboratory tests of grouted rock joints. 38. The effects of the fill material thickness on the tangential stiffness and shear strength of the joints tested by Goodman (1969) are illustrated in fig. 11. The stiffness versus the percent joint filling is plotted in fig. 11a. The stiffness is a measure of the steepness of the prepeak portion of the shear stress versus horizontal displacement curve.

The percent joint filling is defined as ------:-- 100. amplitude of the irregularity Fig. lib shows the relation between the percent joint filling and the shear strength as determined by the peak of the shear stress versus horizontal displacement curve. Both the joint stiffness and shear strength decrease as the percent joint filling increases; however, even at a 125-percent joint filling, the joint stiffness and shear strength are greater than that of the filling material alone. In situ tests of clay-filled fractures in limestone (Case History E-ll) also showed a decrease in strength with an increase in thickness of clay filling. Tests of grouted rock joints yielded similar results (Coulson, 1970). The reduction in strength caused by thick fill layers may be minimized under high normal loads. High normal loads could produce rapid joint closure and possible shearing of the

21 to

Fig. 11. Effect of thickness of joint filling on stiffness and strength (Goodman, 1969)

22 irregularities. Results of tests on clay-filled fractures in limestone (Case History E-ll) defined Mohr failure envelopes that tended to steepen at high normal loads. 39. Test results indicate that when fill layers are very thin, the joint surface irregularities have a greater influence on the resulting strength and deformability of the filled joint. Joint opening during shear observed by Goodman (1969) and Coulson (1970) indicated that sliding up the inclined surfaces occurs, which results in an increased shear resistance defined by an effective i-angle. Coulson (1970) observed that for thin grout layers, the irregularities increase shear resistance by obstructing the formation of Riedel shears within the grout. Riedel shears are a series of failure planes developed during the Riedel experiment (see paragraphs 102 and 103). Similar shear zones have been observed in field tests of filled discontinuities (see Case History B-5) . 40. Tangential stiffness and shear strength are affected by moisture content or pore water pressures within the fill material. Goodman (1969) reported that wet thin seams show a strain-hardening behavior; that is, an increase in shear resistance beyond the initial peak of the shear load versus horizontal displacement curve. An in situ direct shear test of a block resting on a 3/8-in.- thick altered zone in shale exhibited such a strain-hardening behavior (Case History B-5) . The shear stress versus displacement plot from test No. 3 shown in fig. 12 clearly illustrates this type of behavior. In fact, the Mohr-Coulomb shear strength para­ meters corresponding to initial failure were 0 = 14 deg and c = psi; however, at a displacement of 2.0 in., 0 = 18 deg and c = 3 psi. Strain- hardening could possibly be caused by either of two factors. First, the resistance to shear may increase as the irregularities along the joint surface draw nearer to each other. Second, drainage of the fill material during shear may increase both its shear resistance and stiffness. 41. Unlike a relatively clean, rough discontinuity, a filled joint or seam may not exhibit well-defined maximum and residual shear strengths. Tests on discontinuities having smooth walls and filled with wet soft

23 40*0 i i —TEST No! — N ___

A —TE:s t i^o ! — y — i » i | no r - -H — TEST No q{— T y i k TlEST No 7- L_ b

0 0-2 0*4 0-6 0-8 1-0 1-2 1-4 1-6 1-8 2-0 2-2 2*4 2-6 2-8 SHEAR DEFORMATION-Inch««

(A) Temporarily inadequate air supply to pump. (B) Two Hour Cessation of test. (Breakdown in air system.)

Fig. 12. Shear stress versus deformation curves obtained from te sts conducted at a constant displacement rate (Pigot and MacKenz ie , 1964)

24 material may produce shear load versus displacement curves similar to the one shown in fig. 13. A considerable amount of displacement may be re­ quired to reach the residual shear resistance, which may only be slightly less than the maximum shear resistance. The shear behavior of filled dis­ continuities, being dependent on both the rock wall and fill material prop­ erties, is concluded to be complex and somewhat unpredictable. Specimen preparation 42. Design engineers often prefer to have in situ direct shear tests carried out on discontinuities that comprise or form parts of potential failure surfaces in the field. Obviously not all desired test sites are readily accessible. Although critical discontinuities located near the ground surface or previously excavated adits or tunnels can be tested eco­ nomically, tests at these locations may not provide the design engineers with adequate shear strength data. For instance, if boring log studies have revealed an almost inaccessible discontinuity along which sliding could occur and result in a catastropic failure, then the added expense of excavating a test adit may be justified. 43. Excavation procedure. To prevent excessive disturbance, hand­ mining techniques and minimal blasting are generally employed near the proposed test surface. Hand-mining procedures vary from the use of hammers, chisels, and saws to jackhammers, drills, and pavement breakers. The type of tools needed and the amount of disturbance that they are likely to pro­ duce are dependent on the type of rock and the proposed test block dimen­ sions. Test blocks should be formed using the least amount of impact force which is economically feasible. 44. A few cases will illustrate the excavation techniques that have been employed. Not all of the following cases pertain to tests on discon­ tinuities; however, the excavation procedures reviewed can be used in forming test blocks resting on discontinuities. At Jupia Dam (Case History A-2), the 15- by 18- by 18-ft test block was formed by hand tools to minimize disturbance of the basalt-sandstone contact. At Morrow Point

25 SHEAR LOAD F could be obtained from direct shear test of a smooth walled discon­ walled smooth a of test shear direct from obtained be could ig. 13. Plot of shear stress versus horizontal displacement which which displacement horizontal versus stress shear of Plot 13. ig. tinuity filled with wet soft material soft wet with filled tinuity 26 Dam (Case History A-3), mica schist test blocks were reduced to the desired size of 8 by 15 by 15 in. with the use of pavement breakers followed by hand chipping. 45. At Bratsk HEP Dam, large-diameter drill holes were used to form the boundary of the 19- by 23- by 23-ft diabase block. Low-charge blasting and manual work were used to finish forming the block (Case History B-l). Indurated clay, claystone, and shale blocks described by Kenty and Meloy (1965) were cut out with a 20-in. power chain saw. 46. At Carillon (Case History B-5), the rock to be tested was a 6-in.-thick shale containing a thin, altered zone overlain by a massive dolomite. The bedrock overlying the dolomite was first removed. Calyx drill holes 3 ft in diameter were then sunk below the shale bed. Blocks 2.5 by 2.5 ft at their bases were formed by cutting between the calyx holes with wire saws. 47. To aid in reducing discontinuity disturbance during specimen preparation, a small normal load can be placed on the proposed specimen. At Auburn Dam this load was applied with a hydraulic jack (Case History E-17); however, some type of rock anchor can also be used (Case Histories A-l and E-5). At Forebary Dam the stabilizing normal load was produced by tensioning a cable which passed through and was anchored below the test block center (Case History E-5). 48. Specimen size. When testing discontinuities, the question arises of how large a test block is needed. While the specimen height is in it­ self unimportant, the portion of test block above the failure surface should contain as few joints or other discontinuities as possible. An excessive number of joints may weaken the block to such an extent that the applied normal and shear forces cannot be withstood. 49. A major factor in field direct shear tests of discontinuities is the test area. It is more convenient and less expensive to test relatively small areas. In some instances these small-scale tests may be useless; however, the same may be true for large-scale tests for reasons illustrated in fig. 14. In fig. 14a, the shear strengths measured on 6-in. and 3-ft

27 a. SHEAR STRENGTHS MEASURED ON THE 6-IN. AND 3-FT TEST LENGTHS MAY BE COMPARABLE BUT NOT EQUAL TO THE STRENGTH OF THE ENTIRE FAILURE SURFACE

b. SHEAR STRENGTHS MEASURED ON THE 6-IN. AND 3-FT TEST LENGTHS MAY DIFFER FROM EACH OTHER AS WELL AS THE STRENGTH OF THE ENTIRE FAILURE SURFACE

Fig. Ik. Effect of different sizes of specimens (after Deere et al., 1967)

28 test lengths may differ from each other as well as from the strength along the entire surface which can be hundreds of feet long. In fig. 14b, the results of the 6-in. and 3-ft tests may be comparable, but the entire sur­ face could still exhibit a much different shear strength (Deere et al., 1967). The problem becomes even more complicated when the shapes of irregularities in the third dimension of fig. 14 are considered. 50. Test surface areas used for tests of discontinuities are given in table 1 (clean discontinuities) and table 2 (filled discontinuities). Most blocks had base areas of less than 11 sq ft with the smallest being 1 sq ft. The largest block tested had a base area of 1000 sq ft (Case History B-2). 51. Only a few of the references included explanations concerning why a particular test area was chosen. At Muda Dam, one of the main considera­ tions in choosing test surface areas was the required load-pressure range and available loading equipment. Ultimately, a block with base dimensions of 2 by 2 ft (area = 4 sq ft) was chosen for testing mudstone layers in quartzite (Case History B-3). 52. At Bratsk HEP Dam, the diabase block shown in fig. 15 was tested. The block had a height of 19 ft and base dimensions of 23 by 23 ft (area = 529 sq ft) (Case History B-l). The discontinuity tested contained a filling of chlorite and serpentine. Such a large-scale test was deemed necessary after smaller scale tests had convinced the engineers that higher shear strengths were related to greater test areas; whether or not this relation­ ship was confirmed by the large field test was not given in the reference. 53. Large blocks have also been selected to minimize disturbance caused by excavation (Case Histories A-2 and B-9). Large test blocks may absorb most of the energy imparted by excavation tools, thus reducing test zone disturbance. At Mequinenza Dam, a limestone block 3.3 ft high with base dimensions of 13 by 13 ft (area = 169 sq ft) was considered necessary to minimize disturbance of a thin lignite layer (Case History B-9); however, the large-scale test may not have been necessary. The same lignite layer had already been tested by shearing smaller blocks with test

29 Fig. 15. Large diabase block tested in direct shear at Bratsk HEP Dam (Evdokimov and Sapegin, 1964)

30 areas of only 2.7 to 10.8 sq ft (Case History B-8). The shear strength measured by the large-scale tests was only slightly less than that measured by the small-scale tests. 54. Specimen encasement. After the test blocks are cut to the de­ sired size and shape, they can be encased or left exposed during shear. Different types of encasements that have been used include a layer of con­ crete, a steel frame, or concrete or mortar within a steel frame. When shearing a discontinuity, the encasements serve to: a. Provide the specimen with smooth and sound surfaces for uniform distribution of the normal and shear loads. b. Act as reinforcement for weak test blocks during loading. 55. When the test block is left exposed, the normal and shear loads are not usually applied directly to the bare rock surface. Instead, bearing plates or beams transmit and distribute the load across the rock surface. For example, at Jupia Dam the basalt block resting on a thin sandstone layer (Case History A-2) was left entirely exposed and a con­ crete beam was used as the shear load bearing plate as shown in fig. 16. In the tests described in Case History E-2, a layer of concrete was used as the vertical load bearing plate as shown in fig. 17. Chalk blocks resting on 1/2-in.-thick bentonite seams were not encased in tests con­ ducted at Fort Randall Dam (Case History B-10). Steel bearing plates were used to transmit the load across the rock surface as shown in fig. 18. 56. Test blocks are often encased in steel frames, and, unless the rock is very soft and weak, concrete, mortar, or grout is placed between the frame and test block sides with sand, concrete, or mortar placed on the upper surface beneath the cover or loading plate. The filler of concrete, mortar, and sand is needed to provide a smooth contact surface for the steel frame and loading plate. The need for some type of filler between the steel frame and test block is illustrated in fig. 19. The irregular sides and top of the quartzite test blocks formed at Muda Dam required the use of a grout filler to form smooth loading surfaces (Case History B-3).

31 microcrystalline s a n d s t o n e VESICULAR BASALT COMPACT BASALT AND SANDSTONE

PLAN

Fig. 16 Direct shear test setup used at Jupia Dam (Ruiz and Caxnargo, 1966)

32 1. CONCRETE BEARING PLATE 2. ROLLER BEARING 3. STRAIN GAGE OF DYNAMOMETERS 4. HYDRAULIC PRESSES 5. PLASTER LEVELLING WEDGE 6. POINTS AT WHICH THE MOVEMENT ON A PLANE OF MECHANICAL DISCONTINUITY IS MEASURED 7. DISCONTINUITIES TESTED

Fig. 17. Sheax te st of a discontinuity (Drozd, 1967)

33 I.- CONCRETE ANCHOR W/EMBEDDED RAILS. 2 - ^REINFORCING BAR WELDED TO ANCHOR. 3. - LONGITUDINAL RAILS EXTENDING TO ANCHOR. \ 4. -B0ILER TUBING W /S R -4 STRAIN GAGES MOUNTED THEREON. \ 5. -6 " STEEL ROLLERS W/BEARING PLATES. 6. -WOOD AND CELOTEX CUSHION. » 7 -//B E N T O N IT E SEAM. \ 8.-NORMAL OR VERTICAL LOAD, 200 TONS OF RAILS.

Fig. 18. Direct shear test setup used by the U. S. Army Corps of Engi­ neers at Fort Randall Dazn (Thorfinnson, 195*0

34 Outline of Excavation

F ig . 19. Direct shear test setup used at Muda Dam (James, 1969)

35 57. Other test setups utilizing concrete or mortar between the steel frames and test block are shown in figs. 20-23. The setup shown in fig. 20 was used by the U. S. Bureau of Reclamation at Auburn Dam. Mortar was placed on the block's upper surface and between the block's sides and steel frame (Case History E-17). Test blocks used by the USAE Ohio River Division (Case Histories E-8, -9, and -10) were completely encased in hydrostone and steel as shown in fig. 21. The setup shown in fig. 22 was used by the Transportation and Soil Mechanics Laboratory, Spain, to test thin lignite layers in limestone at Mequinenza Dam. Concrete was placed between the block sides and steel frame, while a layer of sand was placed between the upper surface and loading plate (Case History B-8). The setup shown in fig. 23 was used for tests along rock joints (Serafim, 1964) by the National Civil Engineering Laboratory in Portugal (LNEC) and is very similar to that used by the Transportation and Soil Mechanics Laboratory in Spain. The only difference is that vibrated mortar rather than con­ crete is used between the block sides and steel frame. 58. Test blocks have also been wholly or partially encased in con­ crete without the addition of a steel frame. At Harlan County Dam (Case History B-ll), tests were conducted on chalk blocks encased in concrete and resting on bentonite seams. Dolomite blocks overlying an altered zone in shale were encased in 6 in. of reinforced concrete in tests carried out at Carillon near Montreal, Canada (Case History B-5). The diabase block tested at Bratsk HEP Dam was encased in 2 ft of concrete (Case History B-l). 59. At Mequinenza Dam, the top and one side of a limestone test block resting on a lignite seam were covered with 3.3 ft of reinforced concrete as shown in fig. 24 (Case History E-9). Rocha (1964a) described an LNEC test setup that could be used for shearing blocks along discontinuities by making the distance d , in fig. 25, just great enough to prevent the concrete from coming in contact with the test surface. It is important that encasements not be allowed to scrape or gouge the discontinuity being tested since a resistance to shear great enough to affect the test data may result. For example, the results of a test at Morrow Point Dam were

36 Fig. 20. Shear and sliding friction testing equipment used at Auburn Damsite by the U. S. Bureau of Reclamation (Wallace et al., 1970)

37 SECTION

F ig . 21. Direct shear specimen encased in hydrostone and steel and tested by the U. S. Army Engi neer Ohio River Division (Kenty and Meloy, 1965) 1. TRIMMED SAMPLE 2. SAND LAYER 3. RIGID PLATE 4. 50-100 TON JACK 5- 50-TON JACK 6. STRESS TRANSMISSION COLUMN 7. STEEL FRAME 8. REINFORCED CONCRETE

Fig. 22. Concrete and steel encasements used at Mequinenza Dam by the Transportation and Soil Mechanics Laboratory, Spain (Salas and Uriel, 196h). NOTE: Jack capacities are given in metric tons

Fig. 23. Mortar and steel encasements used at Pisoes and Alto Rabagao Dams by the National Civil Engineer­ ing Laboratory, Portugal (LNEC) (Serafim and Folque, 1957; Serafim and Lopes, 1961)

39 1 . JACKS 0.95 x 0.25 M 2. WOOD P L A T E 3. REINFORCED CONCRETE 4. LIMESTONE 5. LIGNITE LAYER 6. 0.95 x 0.50 JACKS

Fig. 2b. Direct shear test setup used at Mequinenza Dam by the Transportation and Soil Mechanics Labora­ tory, Spain (Salas and Uriel, 1964)

Fig. 25. Direct shear test setup used at Alto Rabagao Dam by the National Civil Engineering Laboratory (Rocha, 1964a)

40 useless because the steel frame around the block was binding on the rock surface during shear (Case History A-3). 60. Vertical movement and friction. The loading setup should provide free vertical movement to allow overriding of the irregularities during shear along discontinuities. Friction produced between the normal load mechanism and test specimen should be minimized. This is often accomplished by placing steel roller bearings between the test specimen and hydraulic jack as shown in fig. 17 (Case History E-2). However, such a setup will allow the test block to move from beneath the line of application of the normal force during shear. If the movement is very great, the normal stress will become concentrated on one end of the test surface. This problem can be avoided by placing the rollers between the normal load hydraulic jack and its reaction surface. With such a setup, the hydraulic jack could move with the test specimen. The setup in fig. 26 was the only one described in the literature in which the rollers were placed above the hydraulic jack between the jack and its reaction surface. This setup was used for testing concrete blocks cast on rock surfaces at Bratsk HEP Dam (Case History D-2); however, a similar type setup could be used in trenches or adits for shearing blocks resting on discontinuities. 61. Instrumentation. As part of specimen preparation, instrumentation should be installed to measure both horizontal and vertical displacements. The various uses of displacement observations will be discussed in Part IV of this report. Both mechanical (dial gages) and electrical gages are used for measuring displacements. The electrical devices can be either the resistance or induction (LVDT) types. Readings made with resistance- type gages are subject to variations due to temperature and moisture changes. Steinbichler (1961) prefers the induction-type because they are "almost entirely moisture proof." Often gage readings are recorded automatically by electrical means or by photographing the gages. 62. The number of gages needed for measuring displacement is pri­ marily dependent on the test block length, which is measured parallel to direction of shear. Gages should be placed along the block length to

41 1. TRENCHES 8 . ROLLERS

2. B L O C KS 1 X 1 M 9. ANCHOR IRONS. DIAMETER 100 MM 3. BLOCKS 2 x 2 M 1 0. JACKS 4. HEAT-INSULATION GALLERY (FOR w i n t e r O P E R A T IN G CONDITIONS) 1 1 . SUPPORTING BEAM

5. MOBILE CRANE 12- CENTERING SUPPORT

6. RAILS 13- GAGES

7 . SUPPORTING STEEL BEAMS 14. AN C H O R

Fig. 26 . Direct shear test setup used at Bratsk HEP Dam (Evdokimov and Sapegin, 1964)

42 obtain a complete description of movement along the discontinuity. Closure and opening of the discontinuity during shear is of main interest. There­ fore, gages measuring vertical movement should be placed near the discon­ tinuity whenever readings may be influenced by internal compression or expansion of the test block. 63. A few examples will be given to illustrate the manner in which test blocks are instrumented as well as data recording methods and gage accuracy. Tests carried out at Kurobe IV Dam (Case History E-6) utilized induction-and resistance-type transducers for measuring displacements and all data were recorded automatically by graphical recorders. The accuracy of the measurements, + 0.0002 in., was considered better than that which had been achieved with mechanical devices (John, 1961). 64. The basalt block sheared along a chlorite and serpentine filled joint at Bratsk HEP Dam (Case History B-l) was instrumented with dial gages having 0.0001 or 0.0004 in. divisions. A slide-wire transducer was used to convert the readings into electrical resistance for automatic recording. The 23- by 23- by 19-ft-high block was equipped with 27 gages for measuring vertical displacements and 37 gages for measuring horizontal displacements in the direction of sliding. 65. Dial gages reading to 0.0001 in. were also used by the U. S. Army Corps of Engineers at Fort Randall Dam (Case History B-10) to measure the displacements of chalk test blocks sheared along bentonite seams. The gages were equally spaced along the specimen*s length and mounted on short lengths of 1-in. pipe grouted into the floor of the pit and reading against the steel pins grouted into the sides of the blocks (Thorfinnson, 1954). 66. Dial gages capable of measuring to 0.001 in. were used at Carillon (Case History B-5) for measuring the movement of dolomite test blocks sheared along an altered zone in shale. Three gages were used to indicate vertical movement and two gages measured horizontal movement in the direc­ tion of shear. The gages were mounted on a structural steel frame that was placed over, but independent of, the test block and anchored to the trench

43 bottom and sides. Gage readings were photographed on a centrally located gage panel. 67. At Jupia Dam (Case History A-2), the movements of the basalt test block were measured by ten gages located as shown in fig. 16. The horizontal movement in the direction of shear was measured along three sections, while the vertical movement was only measured along two sections. The gages were located near the discontinuity so that compression of the block material above the gages would not affect the readings. The type and accuracy of the gages used at Jupia Dam were not indicated; however, horizontal and vertical displacements as low as 0.001 in. and about 0.0002 in., respectively, were measured. 68. In tests on mica-schist blocks at Morrow Point Dam, the U. S. Bureau of Reclamation (USBR) used dial gages with 0.001-in. divisions for measuring both horizontal and vertical deformation. The USBR at Auburn Dam (Case History E-17) measured horizontal and vertical displacements with LVDT devices and dial gages. The accuracy of the gages was not given in the reference. 69. Vertical movement within a discontinuity can also be measured with strain gages. By placing strain gages across the discontinuity, iso­ lated measurements of discontinuity closure can be made during consolidation. Whitmore strain gages were installed across bentonite seams along which chalk blocks were sheared at Fort Randall Dam (Case History B-10). 70. Besides measuring vertical and horizontal displacements in direction of shear, lateral movement can also be detected by measuring horizontal displacements perpendicular to a vertical plane through the shear load line of application. Excessive lateral movement or test block turning may not represent actual failure conditions which could occur along the entire discontinuity. Eleven gages were used to measure lateral dis­ placement of the basalt test block at Bratsk HEP Dam (Case History B-l). Two dial gages were used to measure the lateral displacement of the dolomite test blocks at Carillon (Case History B-5).

44 71. Moisture conditions. Before loading, moisture conditions desired on the test surface during consolidation and/or shearing must be considered The effects of moisture on a clean discontinuity are not always predictable Moisture on the surface may act either as a lubricant or antilubricant, de­ pending on the surface mineralogic composition, rate of shear, and sur­ face roughness (Horn and Deere, 1962). Deere et al. (1967) also point out that the influence of pore water pressures within the irregularities along the discontinuities is not understood. Measured strengths along filled discontinuities may be heavily dependent on the moisture conditions of the fill material. Where possible, moisture conditions as indicated in the references have been noted in tables 1 and 2. 72. As an aid to making an accurate estimate of the shear strength, an attempt should be made to keep the moisture conditions along the test surface similar to those that are expected to exist during construction or after completion of the project. Usually, the moisture condition that is considered most critical is chosen for the shear test. For example, joint surfaces located beneath dams are usually kept saturated during testing as recommended by Muller (1961), Rocha (1964a), and Serafim (1964). 73. At the Kurobe IV Dam, the test zones were saturated immediately before testing in order to attain moisture conditions expected to exist when the dam was completed (Case History E-6). At various dam sites in Czechoslovakia, filled discontinuities were completely submerged or con­ tinually watered during testing in an effort to obtain the saturated con­ ditions that were expected to exist after filling the reservoirs (Case History E-2) . 74. The most elaborate test setup used to saturate a specimen was designed by the Transportation and Soil Mechanics Laboratory, Spain (Case History E-12). The entire specimen and test surface was saturated under a constant water pressure and normal stress before shearing was begun. The water was applied through a hole in the cover plate as shown in fig. 27. At the end of the saturation period, which varied from several days to two months, the vertical jacking pressure and water injection pressure were

45 Fig. 2 7 . Direct shear te st setup used atRenegado, Ribarroja, and Santomera Dams by the Transportation and S o il Mechanics Laboratory, Spain (Uriel, 1966)

46 reduced an equal amount in order to maintain a constant effective stress on the test surface. Before shearing, the rubber joint between the lower frame imbedded in the concrete and upper frame surrounding the specimen was removed; therefore, some drainage may have occurred during shear. 75. Attempts were also made to keep discontinuities at their natural moisture conditions. For example, at Fort Randall Dam (Case History B-10) a bituminous sealing compound was used to prevent moisture loss from the chalk blocks and the underlying bentonite seam. Excavation of the test blocks was begun in November, 1949, and was completed in February, 1950. A frame building was constructed over the test area to prevent any freezing and thawing within the specimens. Samples taken after completion of the tests in September, 1950, showed a moisture loss of just 5 percent. Loading procedure 76. The normal and shear loads are applied to the test block as shown in fig. la. Loads are assumed to be transmitted through the block and to the test surface, which is usually located near the base of the block. 77. Normal load. An external normal load was usually applied to even the largest of test blocks (Case History B-2); however, no external normal load was applied to two other large test blocks. The 23- by 23- by 19-ft- high diabase block tested at Bratsk HEP Dam (Case History B-l) and the 18- by 18- by 15-ft-high basalt block tested at Jupia Dam (Case History A-2) were not subjected to external normal loads. Such large blocks are advantageous in that they cover large test areas. The disadvantage of not applying an external normal load is that the normal stress provided by such large blocks is relatively low. The diabase and basalt blocks provided normal stresses of only 21 and 18 psi, respectively. An external normal load can be provided by (a) a surcharge supported by the test block or, in most cases, by (b) hydraulic jacks acting on the test blockfs upper surface. A surcharge load can be quite cumbersome, especially if large normal stresses are desired. A surcharge load was used at Fort Randall Dam (Case History B-10) where railroad rails were piled on a

47 platform supported by the test blocks as shown in fig. 18. The surcharge produced a maximum normal stress of 42 psi. 78. Normal loads are most often provided by hydraulic jacks and measured with conventional pressure gages or load cells. Hydraulic jack loading setups can be used in test adits, trenches, and even calyx drill holes. The setup in fig. 20 is typical of those used inside adits (Case History E-17) where the adit roof provides the reaction for the normal load jacks. When testing in trenches, an anchored or weighted structural bridge is needed to provide the reaction for the normal load jack. Al­ though concrete blocks were tested, the setup shown in fig. 26 is typical of that needed for testing in a trench (Case History D-2). The reaction beam in fig. 26 was fastened to steel rods anchored at a depth of 34 ft. 79. The setup used at Meadowbank Dam is unique since direct shear tests were carried out at the bottom of 4-ft-diam calyx drill holes (fig. 2). Mudstone and sandstone blocks were sheared across silt and clay-filled joints. The vertical jack reacted against a steel beam wedged across the calyx hole (Case History B-4) . 80. Tests should be conducted at normal stresses which encompass those expected to occur during or after the future construction. This is to help prevent the need for extrapolating results into stress ranges other than those used in the tests. For example, at Carillon, (Case History B-5) , blocks were sheared across a 3/8-in.-thick altered zone under normal loads from below to well above those expected to be produced by the dam. Normal stresses applied ranged from about 30 to 100 psi. 81. The desired normal load is usually applied before shearing is begun and held constant during shear. Salas and Uriel (1964) suggest that for tests on foundation rock located at the downstream face of gravity dams, the normal and shear loads should be simultaneously incremented. This type of loading has been utilized in tests of discontinuities (Case Histories B-5, E-14, and E-15), intact rock (Case History E-14), and concrete blocks cast on rock surfaces (Case History D-ll). In Case Histories D-ll, E-14, and E-15, both the normal and shear loads were applied by a single jack

48 inclined as much as 35 deg to the base plane of test blocks. Shear resist­ ance under various normal stresses was obtained by alternating the jack inclination. 82. Simultaneous increase of the normal and shear stresses will affect the shear behavior and measured strength. For example, this type of loading was used for test No. 5 carried out at Carillon on a thin altered zone in shale (Case History B-5). The normal load was applied with a vertical jack and the shear load with a horizontal jack. The shear stress versus shear displacement plot obtained in test No. 5 is shown in fig. 12 along with the plots from tests 1-4 in which shearing took place after consolidation under the applied normal load. In test No. 5, the shear stress increases considerably after initial failure, as shown in fig. 12. This behavior may be the result of an increase in shear strength within the altered zone caused by consolidation within the zone under the increasing normal load. 83. The desired normal load can be placed on the specimen all at once (i.e., instantaneously or as rapidly as possible) or gradually in stages or increments. Stage or incremental loading can be used to simulate the gradual increase in load associated with the construction of a dam. Under incremental loading, a clean discontinuity may undergo a gradual closure accompanied by some crushing along the contact. Even if the nor­ mal load is applied rapidly, time can be allowed for closure along the contact before application of the shear load. 84. More important than the normal loading rate is the time allowed for consolidation before shearing of filled discontinuities. In three tests carried out at Harlan County Dam, bentonite seams were consolidated for 14 to 32 hr before shearing (Case History B-ll). Mudstone seams tested at Muda Dam (Case History B-3) were allowed to consolidate before testing. The coefficient of consolidation of the mudstone was computed by assuming drainage radially, and at the top and bottom of the mudstone. A consolidation time of 3 hr was allowed before shearing along breccia zones in mudstone and clay-filled joints in sandstone at Meadowbank Dam (Case History B-4) .

49 85. The moisture conditions at the beginning of consolidation can also be varied. At Carillon (Case History B-5), a bituminous compound was used to maintain natural moisture conditions before consolidation was begun. The test blocks were of dolomite overlying a 6-in.-thick shale bed. Within the shale bed was a 3/8-in.-thick altered zone in which shearing was to occur. During excavation, the exposed shale face on the specimens was coated with the bituminous compound to prevent moisture loss. Specimens were consolidated from 4 to 20 hr before shearing. At Muda Dam (Case History B-3), blocks of quartzite resting on mudstone seams were kept "soaked or otherwise in a wet condition" (James, 1969) before consolidation was begun. 86. Another problem is determining when consolidation is complete. The procedure was either not given or poorly explained in the case history references. For example, at Mequinenza Dam (Case History B-9), the verti­ cal deformation was allowed to "stabilize" (Salas and Uriel, 1964) before applying the shear load. At Meadowbank Dam (Case History B-4), shearing along a clayey silt zone in mudstone and a clay-filled joint in sandstone began after the dial gages showed "steady conditions" under the normal load (Maddox et al., 1967a, 1967b). Consolidation versus time plots were presented for tests conducted at Carillon (Case History B-5). Consolida­ tion of the shale layer was continued until the rate of consolidation became very small. 87. Shear load. The shear load is usually applied by hydraulic jacks reacting against the wall of the test adit or trench; however, there was one exception. The USAE Ohio River Division used an apparatus in which no external reactions were needed for applying the shear load. The shear rig, containing a 30-ton-capacity hydraulic ram, was placed over the specimen as shown in fig. 21 (Case Histories, C-2, D-4, E-8, E-9, and E-10). 88. In the in situ shear test, the shear load can be applied parallel or inclined to the discontinuity plane, as shown in figs. 16 and 20, respectively. The purpose of the inclined load is to prevent an overturning moment that can reduce the normal stress near the point of shear load

50 application. One obvious disadvantage resulting from the inclined load is that an increment of normal load is added each time the shear stress is increased. The changing normal load causes failure to occur along a stress path different than that produced by a horizontal load (Deere et al., 1967) . This problem may possibly be eliminated by compensating for the normal component of the shear force by reducing the force applied by the vertical jack as was done during direct shear tests at Morrow Point Dam (Case History A-3) . 89. Deere also points out that the use of the inclined shear load can lead to difficulty in interpreting the test results. If the specimen is loaded horizontally, shear stress at failure versus normal stress can be plotted as shown in fig. 28. However, when the inclined shear load is used, data points cannot be obtained in the shaded area shown in fig. 29. 90. The shear load is applied to the test block in increments and at various rates. A test loading rate should be chosen that will simulate the field loading conditions. When testing clay-filled joints, the loading rates should produce pore water pressures similar to those that will be developed in the field problem. For example, at Meadowbank Dam (Case History B-4) , two series of tests were conducted on a silty portion of a breccia zone in mudstone. The first series of tests were conducted at a rate that was suspected of causing excess pore water pressures. Since the actual dam loading was not expected to produce such pore water pressures, a second series of tests were conducted at a much slower rate. Consoli­ dation under the normal stress was carried out for 3 hr, and the horizontal shear stress was applied in increments of 1/2 psi with each increment being held for 15 min after horizontal movement had ceased. 91. The shear strength measured by the second test series was slightly greater than that measured in the first series and may have been the result of an increase in effective normal stress within the fill material. The second loading rate was still considered too rapid and the measured shear strength conservative. Drainage conditions through the joints in the mudstone were considered to be adequate for almost complete

51 o a

O

V- X 5 z o UJ QC h* CO O O cr < UJ I CO EH = S EV = N 6

NORMAL STRESS CTn

Fig. 28. Typical results from direct shear test on intact rock (Deere et al., 1967)

Fig. 29. Typical results from direct shear test on intact rock with inclined shear force (Deere et al., 1967)

52 dissipation of pore water pressures during the actual filling of the reser­ voir. Drozd (1967) suggested that, if possible, pore water pressure within discontinuity filling be measured so that effective stresses can be calculated. 92. When applying the shear load, the rate of stress increase or dis­ placement in the shear direction can be controlled; however, in most cases no control is involved. Stage loading is used in which displacements are observed during each load increment and the following increment is not applied until movement in the shear direction ceases or becomes very slow. For example, in tests described in Case Histories E-8, -9, and -10, load increments were added when horizontal deformation slowed to either 0.001 in./ min or 0.001 in. in three min. 93. Stage loading was also used on the basalt-sandstone contact tested at Jupia Dam (Case History A-2). Additional load increments were not applied until displacements under the present load had ceased. This pro­ cedure of allowing complete displacement under each increment may lead to a conservative estimate of shear strength along the discontinuity being tested. As was shown previously (fig. 7), the shear strength tends to decrease to the residual strength with continued displacement. By allowing the speci­ men to complete displacement under each increment, the shear strength may become progressively less under each following increment. 94. Incremental loading can be used to establish a relatively con­ stant rate of stress increase by applying equal load increments at equal time intervals. Displacements may or may not cease under each increment, depending on the load interval time. A constant rate of stress increase can only be maintained to failure. Once the peak shear resistance is ob­ tained, the applied shear stress must be decreased. The shear stress ap­ plication rate was held constant in tests of a 1/2-in.-thick bentonite seam at Fort Randall Dam (Case History B-10). Load increments were applied at 20- to 40-min intervals with stress rates varying from 0.01 to 0.12 psi per minute.

53 95. In a few of the tests reported, the rate of displacement in the shear direction was held constant. After the maximum shear resistance is reached, the shear stress required to move the block at the constant dis­ placement rate will gradually decrease until the residual shear strength of the discontinuity is obtained. At Carillon (Case History B-5) , shear tests along an altered zone in shale were carried out at a displacement rate that varied from 0.024 to 0.032 in./min. The slow rate of deformation was chosen to simulate conditions that would exist under the dam. Bento­ nite seams tested at Harlan County Dam (Case History B-ll) were sheared at displacement rates of 0.01, 0.02, and 0.1 in./min; the basis for selecting these particular rates was not given in the reference. 96. A rate of 0.05 in./min was used in shearing quartzite blocks along mudstone seams at Muda Dam (Case History B-3). The shearing rate sufficient to allow dissipation of pore water pressures was calculated according to Bishop and Henkel (1957).

Shear of Intact Rock Including Hard Clays and Weak Shales

97. In situ tests are generally only carried out on intact rocks suspected of being unusually weak. Indurated clays, claystones, marls, shales, and various types of weathered rocks are commonly considered for in situ testing. Data from tests of intact rock are given in table 3. A more detailed summary of test procedures and results is contained in the case histories found in the appendixes referred to in the table. Shear mechanism 98. Commonly, rock shear strength is represented in terms of Mohr or Mohr-Coulomb failure envelopes; this convention has been followed throughout this report. Although the Mohr theory is a convenient method of defining shear strength, it offers no description of the shear mechanism. In fact, the shear mechanism of hard intact rock is a controversial sub­ ject and no single theory has been universally accepted. The most widely accepted theories are based on the ideas put forth by Griffith (1921,

54 1925). Griffith hypothesized that tensile stress concentrations develop at the end of microfractures, causing them to propagate when the rock is stressed beyond a certain level. Hard rocks exhibit brittle fracture under ordinary pressures and microscopic observations have revealed the existance of Griffith cracks, particularly along grain boundaries. 99. Bieniawski (1967) describes the mechanism of brittle rock fracture based on the Griffith theory. As load is applied to the rock specimen, the cracks close, followed by linear elastic deformation in the rock. During elastic deformation, energy builds up on microcrack sur­ faces. When the energy reaches a sufficient level, fracture initiation occurs and the cracks begin to grow. Next there is a period of stable crack propagation. Cracks extend along curved paths which tend to become parallel to the major principal stress direction. The propagation rate is slow; if the loading is stopped and the state of stress held constant, the cracks will cease to grow. 100. Stable fracture propagation continues until the critical energy release occurs at about 80-percent maximum stress. At that point unstable fracture propagation begins accompanied by dilatancy. If loading is stopped and the stress level held constant, the energy stored within the rock will continue fracture growth. The velocity of propagation increases rapidly until it reaches a limiting value. At that time, strength failure occurs and the rock loses its load-carrying ability; the rock then ruptures. 101. Maurer (1965) adds that following fracture, the normal stress continues to act across the fracture surface, producing a frictional resistance. Following fracture in direct shear, the block will slide along the fracture surface or, under very high normal stress, a series of new fractures may form as occurred in triaxial tests described by Maurer (1965) . 102. A study of the shear mechanism has also been carried out in direct shear tests of kaolin (Morgenstern and Tchalenko, 1967). Tchalenko (1970) states that most soils and rocks tested in direct shear will develop a shear zone similar to that formed in the Riedel experiment.

55 In the Riedel experiment, a layer of plastic material is placed horizontally over two adjoining platens. One platen is slowly displaced horizontally as shown in fig. 30. The development of the shear zone in the Riedel experiment is shown in fig. 31. The sequence of structures formed during the direct shear test of a kaolin was found to be very similar to those obtained in the Riedel experiment (Tchalenko, 1970). 103. Tchalenko (1970) describes the development of the shear zone shown in fig. 31 as follows. At peak strength, shears were formed as shown in stage a, referred to as the ’’Peak Structure.” During stages b and c, ’’Post-Peak Structure,” some of the present shears extended into a horizontal direction and new shears were formed, connecting pairs of the present shears and displacement was along the shear surface. During stage d, continuous horizontal shears were formed resulting in a ”Pre- Residual Structure.” The ’’Residual Structure” was obtained in stage e where displacement took place almost entirely along a single horizontal shear and the shearing resistance became constant. 104. Intact rock strength is determined by plotting shear load S versus horizontal displacement. The maximum shear strength S . is maximum mobilized at a small displacement where fracture of the intact rock takes place. If further displacement along the fracture or discontinuity is allowed, the minimum shearing resistance S ., will be reached residual (Maurer, 1965; Patton, 1966a, 1966b; TchalenkO, 1970). By testing several specimens at different normal loads, the Mohr failure envelopes of maximum and residual strength can be developed as shown in fig. 32. The inclination of the maximum strength failure envelope is heavy equipment needed to

56 Fig. 30* Diagram of the Riedel experiment (R) Riedel shear, (R') conjugate Riedel shear, (w) width of shear zone (Tchalenko, 1970)

57 ^ 3=

MARKER D 8.90 MM= T O T A L BOARD 1 w- MOVEMENT STAG E a

D = 13.30 MM STAG E b

D = 19.50 MM STAG E C

D = 27.20 MM 1 STAG E d

STAG E e

Fig. 31. Stages of shear zone development in the Riedel experiment (Tchalenko, 1970)

58 F

ig. 32. Maximum andstrengthresidualfailure Maximum envelopes 32.ig. MAXIMUM OR RESIDUAL SHEAR STRENGTH i for initiallyintact specimens for 59 expose the test zone by forming trenches and adits in which the tests are conducted, 106. Only a few references concerned with testing of intact material included a discussion of excavation procedures. Specimens (1 ft by 1 ft by 10 in. high) of indurated clay, claystone, and marl were tested at various dam sites as described in Case Histories C-2 and E-10. A 20-in. power chain saw was used to form the test blocks. Shale specimens (3 by 3 by 1 ft high) tested at Proctor Dam (Case History E-16) were also cut out with a chain saw. 107. Specimen size. Before excavation is begun, the desired size of the test blocks must be determined. The height and base area of in situ specimens that have been tested are given in table 3. Most test blocks had heights less than 1 ft and base areas less than 10 sq ft. The largest test blocks, having heights of approximately 3 ft and 6 ft and base areas of 25 and 100 sq ft (Case Histories E-6 and E-7), were considered to be represent­ ative of the rock mass since each contained a number of randomly oriented natural geological discontinuities. However, the test blocks were oriented to allow failure through intact material. Most specimens are smaller than those described in Case Histories E-6 and E-7, since macroscopic discon­ tinuities are not usually present when measuring intact strength. 108. Specimen encasement. Most intact specimens are encased in a frame, which tends to limit the size of the shear zone. Dvorak and Peter (1961) introduced two simple square steel frames used to test soil of soft rock. The frames are pressed into the ground and then the rock or soil is excavated from around them. The failure zone is located directly beneath the lower edge of the frames. 109. At a dam site in North Bohemia (Case History C-l), both Dvorakfs simple square frame and a double cylindrical frame were utilized in testing claystone blocks. Bukovansky (1966) felt that the double frame was more advantageous than Dvorak's simple frame, since the double frame allowed less exposure of the test block during the block's preparation. The double frame was composed of two cylindrical steel frames, each having a diameter

60 of 2.3 ft. The upper and lower frames were about 5 in. and 2 ft long, respectively. The frames were screwed together and then pressed into the ground (fig. 33a). The material from within the frame was removed down to the desired depth. The bottom of the excavation was then smoothed and covered by a circular loading plate (fig. 33b). Next, the material outside the frame was removed down to 6 in. below the loading plate. The frame was then pressed further into the ground to expose the loading plate as shown in fig. 33c. A cross section of the test setup including the loading equipment is shown in fig. 34. Before shearing, the upper frame was dis­ connected from the lower frame. During shear, only the upper frame was moved. The failure plane was formed between the two frames (see fig. 34); thus only the outer edge of the failure zone was exposed during shear. 110. The main disadvantage of both Dvorak!s and Bukovansky's method is that the frames can only be pressed into soft rock (Bukovansky, 1966). For most rock types, the test blocks have to be formed by regular hand- excavation procedures. The steel frames are then placed around the blocks. 111. In most cases, concrete, mortar, or grout is placed between the sides of the test block and steel frame. Sand or one of the aforementioned materials is placed on the upper surface of the block beneath the loading or cover plate. Shale blocks tested at Proctor Reservoir (Case History E-16) were encased in a steel frame which was grouted into place and is shown in fig. 35. Altered granite specimens sheared at Alto Rabago (Case History C-4) and Pisoes (Case History C-6) dam sites were encased in mortar and steel as shown in fig. 23. A layer of sand was placed beneath the cover plate. The setup was used by the National Civil Engineering Labora­ tory in Portugal. The Transportation and Soil Mechanics Laboratory in Spain used a similar setup (see fig. 27) for testing marl specimens at Renegado and Santomera Dams (Case History E-12). Other setups used on intact rock specimens are shown in figs. 17, 21, and 25, corresponding to Case Histories E-2, C-2, and E-10, and C-4, respectively. As shown in fig. 25, the specimen was encased only in concrete; this type of encase­ ment was used in testing some of the altered granite specimens at Alto Rabago Dam (Case History C-4).

61 b. MATERIAL WITHIN FRAME IS REMOVED AND STEEL LOADING PLATE IS PLACED

Fig. 33. Installation of double cylindrical steel frame

62 Fig. 3^. In situ shear test using a double cylindrical steel frame (Bukovansky, 1966)

63

1961) at at Proctor reservoir

TRUCTURAL BRIDGE S SUPPORTING SURCHARGE LOAD C E L L (GOVT FURNISHED) 64 (USCE, (USCE, FortWorth, Texas, Direct shear test setup used

izm.------m r : Fig. Fig. 35 112. Vertical movement and friction. The loading setup used for testing intact material should allow free vertical movement. Intact speci­ mens have been found to undergo a volume increase during shear. Serafim (1964) considers the "phenomenon analogous to the rheological property of dilatancy that occurs in a plastic body when the yielding point is reached." Friction between the normal load mechanism and specimen should be mini­ mized by using steel roller bearings as discussed previously in "Shear of Discontinuities," Part III. 113. Instrumentation. Gages should be installed to measure vertical and horizontal displacement of intact specimens during in situ shear tests. Types of gages, their accuracy, and recording methods were described in "Shear of Discontinuities," Part III. The displacement of various points on the block should be monitored so that a complete description of the block*s movement during shear may be obtained. 114. Moisture conditions. Another important variable is the moisture conditions within the failure zone. Where data were available in the references, moisture conditions during shearing are indicated in table 3. The most critical moisture condition that may exist at the project site should be chosen for in situ tests. For many tests, an attempt is made to saturate or at least wet the material before consolidation and/or shearing. Altered granite tested at Alto Rabagao Dam was kept saturated during shear (Case History C-4). At Proctor Dam (Case History E-16), natural moisture contents were preserved until just before testing. The shale blocks were treated with latex immediately after excavation. Immediately before testing, the latex was removed. No cracking or drying of the specimens was observed. After applying the normal load, the specimens were flooded. The most complicated method of saturating the specimens was that shown in fig. 27 and used by the Transportation and Soil Mechanics Laboratory in Spain (Case History E-12) in testing intact marl specimens. The specimens were pressure saturated before shearing was begun. 115. Few blocks were sheared under natural moisture conditions. Marl and soft shale specimens (Case Histories C-2 and E-10) were kept at their

65 natural moisture content by placing wet burlap over the specimens before testing. Claystone blocks (Case History C-l) were also sheared at their natural moisture content. At Santomera Dam (Case History E-12), argil­ laceous marl blocks were sheared under both saturated and natural moisture conditions. The highest shear strength was obtained under natural moisture conditions. Loading procedure 116. Intact specimens are usually loaded in the manner illustrated in fig. lb with failure occurring within a zone located near the base of the block. The normal and shear loads are provided by hydraulic jacks as shown in fig. 23. The vertical jacks react against the test adit roof or anchored reaction beams in supplying the normal load. The shear jack generally reacts against the walls of test adits or trenches. One excep­ tion was found in which the shear apparatus containing a 30-ton-capacity hydraulic ram was placed over the specimen. As shown in fig. 21, no external reactions were needed for applying the shear load. Failure occurred through a zone located about 5 in. above the base of the block (Case Histories C-2 and E-10). 117. Normal load. Tests should be conducted under normal stresses that encompass those expected to be produced during construction or after completion of the project. The normal load can be applied incrementally or all at one time and is usually held constant during shear. At Alto Rabagao Dam (Case History C-4), the normal load was applied incrementally to altered granite test blocks. The normal stress was applied as ’’instantaneously as possible” to shale blocks sheared at Proctor Dam (Case History E-16). 118. The time allowed for consolidation before shearing can also be varied and should depend upon the actual field loading conditions. At Alto Rabagao Dam (Case History C-4) , the shear load was applied to the altered granite specimens only after vertical displacements had stopped. Shale blocks tested at Proctor Dam (Case History E-16) were allowed to consoli­ date 24 hr before application of the shearing stress. The consolidation

66 plots indicated that primary consolidation was complete. The degree of saturation of the specimens at the beginning of consolidation can also be altered to conform to actual loading conditions, as was discussed under "Shear of Discontinuities," Part III. 119. Shear load. As previously mentioned under "Shear of Discon­ tinuities," the shear load can be applied inclined or parallel to base plane of the test block. The inclined shear load is used to avoid an overturning moment which can reduce the normal stress near the shear- loaded side of the test block. In intact rock, the normal stress may even become tensile. The problems presented by the inclined shear load have been discussed. In addition, studies carried out by Lorente (1968) show that even with an inclined shear load, a tensile normal stress can be developed in intact material. 120. The rate at which the blocks are sheared can also be varied to meet field loading conditions. The rate of stress increase can be held constant by applying equal load increments at equal time intervals. For example, shale blocks at Proctor Dam (Case History E-16) were sheared at a stress rate of approximately 0.03 psi/min. This rate of shearing was& determined as that needed to produce failure in 24 hr. The rate of dis­ placement in the direction of shear can also be controlled as was described in "Shear of Discontinuities," Part III. 121. In most tests on intact blocks, the rate of shear displacement or stress increase is not controlled. Usually increments of shear load are simply applied when the shear displacement under the previous increment ceases or becomes very slow. In tests described in Case Histories C-2 and E-10, shear load increments were added when deformation slowed to 0.001 in. in 3 min. In tests carried out at Alto Rabagao Dam (Case History C-4), shear load increments were applied only after displacements under the previous increment had stopped.

67 Shear of Concrete Blocks on Rock Surfaces

122. Concrete blocks have been sheared across a variety of rock-type surfaces, which are listed in table 4. Tests of this nature are usually conducted for the purpose of measuring either the shear resistance along the concrete-rock contact or the shear strength of the rock immediately beneath the concrete. Concrete block shear tests are relatively simple to carry out; however, interpretation of the test results may be difficult. Shear mechanism 123. In a direct shear test of concrete on rock, the specimen is loaded as shown in fig. lc. The shear mechanism active during failure is dependent on the location of the failure surface, which can occur along, near, or through the concrete-rock bond. The potential failure zone is depicted in fig. lc. The location of the failure surface is governed by the interrelationship between the concrete shear strength, bond shear strength, rock shear strength, and the magnitude and distribution of normal and shear stresses within the potential failure zone. 124. When the bond strength and rock strength exceed that of the concrete, shear may occur entirely within the concrete as shown in fig. 36a. The shear mechanism begins with brittle fracture of the concrete followed by sliding along the fracture surface. 125. When the bond strength along smooth contacts is much less than that of the rock or concrete, shear may occur mainly along the concrete- rock contact as shown in fig. 36b. The shear mechanism includes initial failure of the bond followed by sliding along the concrete-rock contact. Sliding along the contact can be accompanied by some disturbance to the rock directly beneath the contact. In two tests described in Case History D-7, sliding occurred along the concrete-shale contact; however, "small cracks appeared in shale immediately beneath the test blocks" (Niederhoff, 1939). Shear along contacts can also be more complicated where the rock surface contains a number of irregularities or protusions. In tests carried

68 RUPTURE-!

^ BLOCK %ì

— s 1 1 1 1 1 "L 1 ' H b __T - 1 1 1 1 COMPACT DIABASE a. SHEAR ENTIRELY WITHIN CONCRETE b. SHEAR ALONG THE CONCRETE- ROCK CONTACT

LINE OF RU PTUR * BLOCK *N

M ili 1 i l (PACT DIABASE ^

C. SHEAR ENTIRELY WITHIN ROCK d. SHEAR WITHIN CONCRETE AND ALONG CONCRETE-ROCK CONTACT

Fig 36. Location of failure surfaces for concrete block tests at Bratsk HEP Dam (after Evdokimov and Sapegin, 19 6b)

69 out at Bratsk HEP Dam (Case History D-2), rock protrusions were often sheared off during sliding. 126. Where the foundation rock is fairly weak, shear may occur en­ tirely within the rock beneath concrete-rock contact as shown in fig. 36c. Shear may take place through intact rock or possibly along shallow discon­ tinuities subparallel to the concrete-rock contact. At Watts Bar Dam (Case History D-8), shear took place within the shale about 1/2 to 2 in. below and essentially parallel to the concrete-shale contact. As sliding progressed, protrusions along the failure surface were sheared off, indi­ cating that once the failure surface is formed, the shear mechanism is likely similar to that which occurs when shearing along discontinuities. 127. Concrete block tests can also involve a complicated shear mechanism in which parts of the shear surface occur within the concrete, along the concrete-rock contact, and within the foundation rock. Failures of that type occurred at Bratsk HEP Dam (Case History D-2). One such failure is shown in fig. 36d where the failure surface passed through the concrete and along the concrete-rock contact. In cases such as these, different shear mechanisms are likely to be operative at different stages of failure. Thus, the formation of the failure surface should be observed whenever possible while shearing concrete blocks cast on rock surfaces. 128. The above concepts lead to a very important conclusion. In general, the concrete block shear test only measured the shear strength along or very near the concrete-rock contact and does not give a complete description of the foundation shear strength. Weaker joint surfaces or shear zones may exist only a few feet below the surface. For example, the cross section of the Millers Ferry Dam, shown in fig. 37, indicated three potential failure surfaces. Specimen preparation 129. Excavation procedures. Excavation is sometimes needed to expose and prepare the rock surfaces that are to be tested. Where the rock shear strength is desired, careful excavation is demanded to prevent excessive disturbance of the test zone. Once the test surface is exposed, the surface

70 E L 34.6 M

Fig. 37. Cross section of Millers Ferry Dam and foundation (after Corns and Nesbitt, 1967)

71 should be cleaned to ensure a strong concrete-rock bond. Where the contact strength is to be measured, excavation should proceed in a manner similar to that which will be used during construction. Test surfaces should also be prepared or left in the same condition as that to be used in construc­ tion. In tests described in Case History D-4, concrete was cast on clay- stone, shale, and marl surfaces. The surfaces were cleaned, a 1-1/2-in.- thick layer of grout was placed on the surface, followed by the concrete. The procedure was designed to simulate field conditions where a layer of grout is placed on the bedrock before placement of the concrete structure. At Possum Kingdom Dam (Case History D-7), concrete blocks were case on irregular shale surfaces formed by air tool and hand excavation. The irreg ular surfaces were expected to be representative of those upon which the dam would rest. At Bratsk HEP Dam (Case History D-2), blocks were case on prepared surfaces of different roughness in order to study the effect of roughness on contact shear strength. 130. Specimen size. In concrete block tests, the test area size is the main concern. When measuring contact strength, an area should be used that is representative of the entire surface upon which the concrete structure will rest. Even where the surface is fairly uniform, the test block should cover a large enough area to prevent any local weak points in the bond from having a great influence on the test results. In most cases, the base area of concrete blocks is equal to approximately 10 sq ft or less. The largest concrete block is shown in fig. 38. The block was about 6 ft high with a base area of 100 sq ft and was tested at Kurobe IV Dam (Case History E-6) . 131. Encasements. Concrete blocks are not generally provided with any type of encasements such as those used in tests of intact rock speci­ mens or rock blocks resting on cleaned or filled discontinuities; however, in some cases, the blocks contain steel reinforcement for added strength as shown in fig. 39 (Case History D-l). Steel encasements were utilized in tests conducted at Belleville, Cannelton, and Jones Bluff Lock and Dams by the USAE Ohio River Division (Case History D-4) and at Proctor Dam

72 © CONCRETE BLOCK (g) 12 PISTON JACKS (CAPACITY: 300 ton X 12 = 3600t0n) FOR TANGENTIAL LOAD

( D 6 PLAT JACK SANDWICHES (CAPACITY ! 1000 tonX 6 = 6000 ton) FOR NORMAL LOAD

Fig. 38. Direct shear test setup used at Kurobe IV Dam (Nose, I 96L). NOTE: Jack capacities are given in metric tons

•Fig. 39- Direct shear test (Dvorak, 1957)

73 (Case History E-16). No other tests were reported in which concrete blocks were encased. 132. Vertical movement, friction, and instrumentation. Free vertical movement should be provided and friction minimized with the use of steel roller bearings as shown in fig. 39. Gages should be installed for measure­ ment of both horizontal and vertical displacements as previously discussed in "Shear of Discontinuities," Part III. These measurements may later be helpful in interpreting the test results. 133. Moisture conditions. When measuring contact strength, moisture conditions within the rock immediately beneath the concrete blocks should be similar to those that will exist after placement of the concrete struc­ ture. Where the foundation rock is expected to remain dry, some time should be allowed for drying before casting the concrete blocks. Where the sur­ face rock is expected to remain at its natural water content, the rock should be protected from moisture loss before casting and shearing the concrete blocks. At the Possum Kingdon Dam (Case History D-7), a coating of asphalt sealing solution was applied to prevent moisture loss from the shale. The concrete blocks were cast directly on the asphalt solution; however, the sealant could have been removed from the test area just before casting the concrete blocks. A coating of latex may also be placed on the test area and removed before testing as was done at Proctor Dam (Case History E-16). 134. Where saturated or very moist conditions are expected, the test surface can be flooded either before or after casting the concrete blocks and the water drained off just before testing. At Kurobe IV Dam (Case History E-6), test zones were saturated immediately before testing. The concrete-rock contacts were kept submerged during testing at Bratsk HEP Dam (Case History D-2). Loading procedure 135. Concrete blocks are usually cast on the rock surface and loaded in direct shear as shown in fig. lc. Failure may occur anywhere within the zone indicated in fig. lc. A slightly different type setup used by

74 the USAE Ohio River Division (Case History D-4) may aid in restricting shear to the concrete-rock contact. The test setup is shown in fig. 21. After shearing blocks of claystone, shale, and marl, a 1-1/2-in.-thick layer of grout followed by concrete is cast on the sheared surfaces. The upper half of the steel shear box filled with concrete is sheared across the lower half, causing failure to occur in a narrow zone along the contact area. In none of the tests did shear occur within the rock alone. 136. Normal load. The normal load is generally applied by hydraulic jacks as shown in figs. 26, 40, and 41, corresponding to Case Histories D-2, D-7, and D-6, respectively. The stresses should at least encompass those predicted to act on the complete structure. 137. The unusual loading setup shown in fig. 42 was used at the Farahnaz Pahlavi Dam in Iran (Case History D-10). The shear load was applied with flat jacks to opposite sides of the test block and the normal load was provided by posttensioned cables anchored directly beneath the block as shown in fig. 42. The shear load produced by the active flat jack was resisted by the passive jack load and the shear resistance along the rock-concrete contact; however, the block was sheared to failure only after the passive jack was removed. The purpose of the passive jack was not explained in the reference. 138. In some cases, time may be allowed for consolidation under the normal load before applying the shear load. For example, if shear is ex­ pected to occur along a discontinuity directly beneath the proposed con­ crete structure, the vertical load can be applied gradually allowing for some closure of the discontinuity. Consolidation has been previously dis­ cussed under "Shear of Discontinuities," Part III. 139. Shear load. The shear load is usually applied with hydraulic jacks either horizontal (see figs. 26 and 40) or inclined to the test block base (see figs. 39 and 41). Problems associated with the horizontal and inclined shear loads have been previously discussed in "Shear of Discon­ tinuities," Part III.

75 Fig. 40. Direct shear test setup used at Possum Kingdom Dam, Texas (Niederhoff, 1939)

Fig. 4l. Direct shear test setup used at Shijushida Dam (Multipurpose Dam Pock Testing Group, 1964)

76 F ig . h2 . Direct shear test setup used at Faranaz Pahlavi Dam (Scott et a l., 1968)

77 140. The rate of shear stress application or the displacement rate can be controlled as was previously discussed in ’’Shear of Discontinuities,” Part III. At Proctor Dam (Case History E-16), increments of shear load were applied at equal time intervals to establish constant stress rates of approximately 0.01 and 0.04 psi/min, resulting in average displacement rates as low as 0.0001 in./min. In most tests, stress application or displace­ ment rate was not controlled. The shear stress was simply applied in increments with displacement ceasing or becoming very slow between incre­ ments. Various average rates of shear stress application and displacement were thus established. At Watts Bar Dam (Case History D-8), concrete blocks on shale were sheared at average stress rates ranging from 0.8 to 5 psi/min. At Possum Kingdom Dam (Case History D-7) , average stress rates of about 0.75 and 1.0 psi/min were established with a corresponding average horizontal displacement rate of about 0.005 in./min.

78 PART IV: INTERPRETATION OF IN SITU DIRECT SHEAR TEST RESULTS

Introduction

141. Proper interpretation of the test data is required to arrive at a quantitative estimate of the shear strength and deformation characteristics of the zones tested and to ascertain the applicability of test results to other locations within the rock mass. Proper interpretation depends on (a) the purpose for which the tests were conducted; (b) the properties of the zones tested; (c) the conditions, procedures, and equipment that were employed during the test; and (d) the active shear mechanism. These factors mainly influence the choice of failure criteria and the determination of failure envelopes defining the strengths of discontinuities or zones tested.

Failure Criteria

142. Before the direct shear test is begun, the engineer should determine how failure will be defined. After establishing the failure criteria, the engineer is more capable of selecting the variables that must be observed during the test and the point at which the test can be discontinued. The failure criteria should also accompany the presentation of any failure envelopes which are used in design. 143. Various failure criteria have been discussed in the literature (Haverland and Butler, 1970; Ruiz and Camargo, 1966; Ruiz et al., 1968; Serafim, 1964; Serafim and. Guerriero, 1968). Common failure criteria are a. Maximum shear stress criterion: the maximum shear stress that can be mobilized during the test. b. Residual shear stress criterion: the minimum constant shear stress required to produce continued displacement.

79 c. Displacement criterion: the shear stress mobilized at a particular horizontal displacement. d. Dilatance or inversion point criterion: the shear stress corresponding to the point at which the vertical displace­ ment changes from downward to upward. Once the failure criterion is chosen, the corresponding shear stress and normal stress are used to determine a failure envelope. Where possible the failure criteria are given in tables 1-4. Maximum and residual shear stress criteria 144. Designers are commonly interested in the maximum available

shear strength. The maximum shear stress points are identified as t max in fig. 43. The maximum shear stress usually corresponds to the peak of the shear stress versus displacement plot (curve a of fig. 43); however, some confusion may arise where strain-hardening is encountered. Strain­ hardening was exhibited by a 3/8-in.-thick altered zone in shale as shown by test No. 3 in fig. 12 (Case History B-5). An initial peak occurred at a displacement less than 0.05 in., followed by an increase in shear stress to a value greater than the initial peak. When this happens, the first peak is termed the maximum shear stress corresponding to initial failure and the latter is the ultimate shear stress. As used here, the term ultimate implies that there exists an initial peak at a much lower displacement. 145, If the residual shear strength is to be determined, then dis­ placement is continued until the shear stress approaches the horizontal

asymtotic value of residual shear stress t (curve a of fig. 43) . When K the zone tested exhibits only a residual shear strength, curve b of fig. 43 may be obtained. In such cases, the maximum shear stress attained is the residual shear strength. By testing a number of specimens, each at a different normal load, the maximum and residual strength failure envelopes, such as those in figs. 32 or 44, are developed by plotting maximum and residual shear stresses versus corresponding normal stresses.

80 i. 3 Po showing Plotandshearstress, residual maximum U3.Pig.

SHEAR STRESS T and criteriadisplacementfailure H RZNA DSLCMN X DISPLACEMENT ORIZONTAL 81

F SHEAR STRENGTH ig. . Maximum and residual strengthand failure residualenvelopes from Maximum tests . ig. fdsotniis (afterofdiscontinuitiesetal., Deere 82 1967)

146. Attempts have also been made to use repetitive testing to deter­ mine maximum and residual strength failure envelopes for discontinuities. This type of testing has been used extensively for in situ direct shear tests as indicated in tables 1-4. 147. In repetitive testing, a specimen is initially sheared until failure (maximum shear stress criterion) is imminent or is actually ob­ tained. The shear load is then released and the block resheared under an increased or decreased normal stress. In some cases, the specimen is returned to its original position before reshearing. Repetitive testing can be useful; however, the test results are difficult to interpret, since after initial shearing the discontinuity surface undergoes irreversible changes that influence the results of succeeding tests. The failure envelopes obtained from repetitive testing will usually define strengths intermediate between the maximum and residual strength. The shapes and locations of the failure envelopes will also depend on whether increasing or decreasing normal loads are used. In general, repetitive testing will yield a conservative estimate of the maximum shear strength. 148. Repetitive testing may be conveniently used to measure the residual shear strength. Continued displacement ultimately reduces the strength available along the discontinuity to its residual shear strength. After a number of repetitions, the maximum stress is, in fact, the residual stress (curve b, fig. 43). Displacement criterion 149. In some cases, the shear stress required to produce a particular horizontal displacement is used for plotting a failure envelope. This shear stress t A can correspond to any displacement, such as X- , x0 , or x_ A 1 2 3 shown in fig. 43, and is not necessarily equal to the maximum or residual shear stress. Shear strength envelopes corresponding to displacements, such as x^ and x^ in fig. 43, are used to show the decrease in strength with displacement.

83 Dilatance or inversion point criterion 150. The inversion point or dilatance criterion is dependent on the vertical displacements that occur during shear. From tests of weathered granite (Case History C-4), Serafim (1964) found that the vertical dis­ placement is downward during the first portion of the direct shear test, but later it changes to upward as shown in fig. 45. Serafim stated that the shear stress initiating failure corresponds to the point where the vertical displacements change from downward to upward (point A of fig. 45) . Serafim felt that the change from volume decrease to volume increase is similar to the property of dilatancy, which is encountered in the yielding of a plastic body, and that rupture begins at the inversion point. 151. Inversion is also likely to occur when shearing along discon­ tinuities. Initial downward displacement could be caused by continued closure of the discontinuity under the normal load. Upward displacement would take place when the test block begins sliding up the irregularities as shown by Patton (1966a, 1966b). 152. The inversion point has been found to occur at a shear stress less than the maximum shear stress and at a horizontal displacement less than that required for peak shear. At Morrow Point Dam (Case History A-3), the inversion point occurred at a shear stress equal to less than half the maximum shear stress shown in fig. 46. Tests on intact blocks (Case History C-5) resulted in a maximum shear stress only slightly greater than the shear stress corresponding to inversion.

Failure Envelopes

153. Mohr failure envelopes are determined by plotting shear stress versus normal stress at failure. Most often the maximum and residual shear strength envelopes are desired. Residual strength data many times are defined by a Mohr-Coulomb straight-line approximation; however, maximum shear strength data may best be defined by a curve. In fig. 32, typical maximum and residual shear strength envelopes are shown from tests on intact

84 Fig. Fig.

iet ha o atrd rnt seies t lo aaa Dam Rabagao (Serafim Alto at specimens granite altered of shear direct TANGENTIAL STRESS T k g c m ' 1 + 5 Ser tes ess erial ipaeet uvs band from obtained curves displacement l rtica ve versus stress Shear . V RIA DSLCMN ( ) m (m DISPLACEMENT ERTICAL n Lps 1961) Lopes, and 85

F ig . h6. Shear stress versus vertical displacement curves obtained from direct shear tests of mica schist specimens at Morrow Point Dam (USER, 1965)

86 rock. Both envelopes are generally straight lines over small ranges of normal stress. The maximum shear strength is defined by

T = C + C tan 0. (3) n i where c = cohesion intercept 0^ = angle of internal shear strength

The residual strength envelope is defined by

t = °n tan 0r (4)

154. In the case of joints, the failure envelopes will most likely be based on a knowledge of the shear mechanism along discontinuities. For example, fig. 47 shows maximum shear strength data similar to that which could be obtained from a direct shear test on an irregular rock contact. A straight-line failure envelope is often drawn through the data as shown in fig. 47. From the study of shear failure along clean discontinuities presented in Part III, it can be seen that the straight-line interpretation may be in error. The maximum strength failure envelopes expected are similar to those shown and defined in fig. 44. The actual maximum strength envelope is curved, but is usually approximated by two straight lines. Thus, the data points in fig. 47 may better be described by the curved failure envelope also shown in fig. 47. By comparing the two envelopes, it can be seen that there are two portions of the straight-line envelope that may lead to an overestimate of the available shear strength. 155. The complex nature of shear along filled discontinuities may or may not result in a maximum shear strength envelope similar to that shown in fig. 44. Unless a sufficient number of tests have been conducted at a wide range of normal loads, the data should be fitted to maximum and resi­ dual strength envelopes similar to those in fig. 44. This type of envelope will not likely overestimate available maximum shear strength. 156. The general shape of the envelope obtained from tests of concrete blocks cast on rock surfaces is dependent on the failure surface location.

87 MAXIMUM SHEAR STRESS P g. +. pcl a oband rm di ser t s e t shear t c e ir d a from btained o ta a d ypical T 1+7. . ig a scontnuity u tin n o c is d a f o 88 Shear can occur anywhere along, near, or through the rock bond. Initial failure along the contact or shear through the rock will likely result in an envelope similar to that for intact rock. Continued shear along the contact will then result in failure envelopes similar to those obtained for discontinuities. Where shear is not limited to just along the contact or through the rock, the maximum strength envelope may or may not be subject to approximation by one or more straight lines; however, the residual strength will likely be approximated by a straight line. 157. The information presented with strength test data should include the following: a. A description of the zone tested (intact or discontinuity). b. Size of test block and shear surface area. c. Failure criteria and displacement at failure. d. Test procedure. e. When a discontinuity is tested, include the i-angle estimated from surface geometry and the test results. Determination of i will be discussed subsequently. All of this information is needed to aid the designer in utilizing the failure envelopes.

Data from Displacement Observations

158. Horizontal and vertical displacements are measured during field direct shear tests. These data can be used for various purposes. As was mentioned in Part III, the influence of the irregularities on the shear strength along a discontinuity is represented by the i-angle, which can be measured from a plot of vertical versus horizontal displacements as shown in fig. 48. Shearing at low normal loads is accompanied with vertical displacements caused by the block sliding up the irregularities. At high normal loads, the irregularities are sheared off; therefore, vertical dis­ placement is greatly reduced. A knowledge of the normal load a A at j HL

89 VERTICAL MOVEMENT F g. +. optto of he iangle g n i-a e th f o Computation 1+8. . ig 90 which this reduction in vertical displacement occurs is sometimes helpful when reducing the maximum strength failure envelope to two straight lines as shown in fig. 44. 159. Information about the stresses on the test block can be obtained from displacement and strain observations. In tests described in Case Histories A-2, B-10, and E-ll, horizontal displacements were noted as being greater near the load application point. This may indicate that the shear stress is highly concentrated at that point. Similarly, upward displace­ ments were greater near the load application point (Case History A-2), thus indicating a tilting of the block possibly accompanied by a reduction in normal stress. When testing discontinuities, horizontal and vertical strain gages placed near the discontinuity can detect any gross irregular­ ities in the normal and shear stress distributions. Vertical strain measurements can also be used to obtain the modulus of elasticity E of the test block.

160. An estimate can be made of the modulus of elasticity E of the rock mass by measuring displacements below the test block. The vertical load must be applied in stages and relative vertical displacements below the test block are measured by extensometers anchored in small-diameter drill holes around the test block. 161. When the finite element method is to be used in analyzing a jointed rock mass, parameters reflecting the joint stiffness can be deter­ mined from displacement data (Goodman et al., 1968). Failure must take place along a discontinuity. The parameters which must be determined are unit stiffness across the joint (normal stiffness) K and unit stiffness n along the joint (tangential stiffness) . The test block is considered to have a test length L and unit width. The normal stiffness is deter­ mined from a plot of the applied normal force per unit length Fr/L versus the joint normal deformation W . The joint normal deformation n includes only the closing or compression of the joint. The tangential stiffness is found by plotting the applied shear force per unit length

91 F /L versus the tangential deformation W . The unit normal and unit s s tangential stiffness are given by the slopes as shown in fig. 49.

Reliability of Test Results

162. Before utilizing the test results, their reliability should be analyzed. The shear strength derived from the direct shear test only approximate the real shear strength, which is always an unknown. For that reason, only a qualified rock mechanics engineer who is familiar with the test location, procedure, and interpretation should attempt to apply the test results. 163. The main factors that produce the uncertainty in the test results are (a) disturbance created during specimen preparation, (b) the unnatural stress conditions or displacements that occur within the test specimen and along the failure surface, and (c) load and displacement measurement errors caused by equipment and instrumentation and errors caused by misreading a gage or miscalculating a load or displacement. 164. The unnatural stress conditions and displacements that occur during a field direct shear test are responsible for much of the uncertainty in the test results. For instance when testing a shear zone or filled joint, the fill material may flow out from within the joint (Case History E-2) . The flow out of material may not be representative of actual failure along the entire joint surfaces. Squeezing out of fill material could result in a high measured shear strength because better contact would be made between the irregularities. 165. Another problem is presented by possible turning and twisting of the test block during shear. Movement in the plane of the failure sur­ face perpendicular to the shear direction would not likely take place during actual shear failure in nature. 166. As previously mentioned, blocks may undergo nonuniform displace­ ment. Greater horizontal displacement tends to occur near the point of load application (Case Histories A-2, B-10, and E-ll) . This nonuniform

92 Fig. k $ . Data from a hypothetical direct shear test of a rock joint (Goodman et al., 1968)

93 horizontal displacement accompanied by tilting of the test block indicates that a nonuniform stress distribution may exist across the failure surface 167. A unique problem related to concrete block tests was brought out in tests at Proctor Dam (Case History E-16). Failure in the concrete block tests occurred entirely within the rock; however, the strength measured in those tests was greater than the strength measured in tests of intact rock specimens. This phenomenon was attributed to the removal of moisture from the shale during the concrete*s hydration, which caused the shale within a few inches of the block base to become harder and stronger.

Application of Test Results

Intact rock 168. For an in situ direct shear test to be useful, the results must be applicable to the entire discontinuity or zone tested and possibly applicable to other discontinuities or zones existing in the field. The results of tests on intact rock are assumed to apply directly to other in­ tact zones of similar material existing within the mass. Difficulty arises where intact zones of interest are essentially the same as the material tested, but differ in properties such as density, porosity, or moisture content. In those cases correlations are helpful in applying test results. For example, the National Civil Engineering Laboratory, Lisbon, Portugal (Rocha et al., 1967; Rocha, 1964a; Serafim, 1964) correlates shear strength with an alteration or quality index I defined by:

I = p ~ P X 100 (5) P where P = weight of a saturated rock sample p = weight of the rock sample after it is dried at 105°C The quality index is essentially equal to the moisture content of the rock sample when it is saturated and is an indication of the rock*s porosity.

94 169. Correlation of the strength parameters 0^ and c with the alteration index were obtained from a series of in situ direct shear tests of weathered granite at Alto Rabagao Dam (Case History C-4) and are shown in fig. 50. Both the angle of internal friction 0^ and the cohesion intercept c decrease as the alteration index increases. The rock having an alteration index above 15 was actually a residual soil that disintegrated in water. Discontinuities 170. The results of tests on discontinuities are commonly applied by assuming the tested portion to be representative of the entire discontinuity. Therefore, the measured shear strength is assumed to be the governing shear strength along the entire discontinuity. This assumption may be valid if the discontinuity is very planar (cross section has straight-line appearance) and exhibits relatively uniform physical characteristics. However, many discontinuities are irregular to wavy, causing the in situ test area to be unrepresentative as shown in fig. 14. 171. A method of applying shear strength values from discontinuity tests to the potential failure surface follows from the shear mechanism along irregular surfaces (see Shear of Discontinuities, Part III). The method may also prove useful in extrapolating the results of concrete block shear tests in which failure occurs along the concrete-rock contact. 172. The method utilizes the i-angle, which is the effective incli­ nation of the irregularities with respect to the average dip of the dis­ continuity in question. The i-angle represents the shear resistance contributed by the irregularities until they are sheared off at their base under a sufficient normal stress. Throughout this range of normal loads, the Mohr-Coulomb shear strength envelope is defined by t = a tan (0^ + i) as indicated in fig. 44. 173. When applying shear test results over the entire discontinuity, the residual strength 0^ is assumed to be the same over the whole discon­ tinuity surface. The only variable is, therefore, the effective i-angle. The residual shear strength is measured by the in situ direct shear test,

95 Quality index ( i)

Fig. 50. Correlation of the cohesion intercept and angle of internal friction with the quality index (Rocha et al., 19^7)

96 and the effective i-angle along the entire discontinuity is determined from field observation. Estimating the effective i-angle can be quite difficult. However, studies by Patton (1966a) of over 300 rock slopes indicated that the first-order irregularities shown in fig. 51a control the shear strength along the discontinuities. The second-order irregularities shown in fig. 51b are sheared off through progressive failure (Deere et al., 1967). 174. For comparison with the effective i-angle along the entire dis­ continuity, the effective i-angle of the portion tested can be determined from either strength or displacement data. The i-angle is equal to the angle between the maximum and residual shear strength failure envelopes shown in fig. 44, or i is measured by interpreting vertical versus horizontal displacement as shown in fig. 48. If the test specimen contains an inclined failure surface as shown in fig. 52a, and the displacements are measured in the normal and shear direction, the calculated i-angle will include the angle a . The i-angle computed as shown in fig. 48 must be reduced by the angle o' . For an inclined failure surface, the true resi­ dual strength and initial portion of the maximum strength envelope must also be reduced by the angle a as shown in fig. 52b. 175. The equation T = an tan (0r + *•) only defines the shear strength along a discontinuity at low normal loads (line OA of fig. 44). The maximum strength envelope is commonly approximated by two straight lines as shown in fig. 44 (lines OA and AB). Ideally, line AB (determined from in situ tests) should apply directly to the entire discontinuity independently of the effective i-angles as shown in fig. 53. However, analysis of data obtained by Patton (1966a) from tests on plaster-of-paris specimens con­ taining inclined teeth resulted in failure envelopes similar to those shown in fig. 54. Stresses along lines AB and A fB! were determined by dividing the normal and shear loads by the base area of the teeth. The lower strength (line AB of fig. 54) of the steeper teeth, i^ is likely due to their susceptibility to progressive and tensile failure. 176. Based on the behavior illustrated in fig. 54, it can be assumed that where the observed effective i-angle along the entire

97 Fig. 51. An example of a discontinuity illustrating first- and second- order irregularities (Deere etal., 1967) N

q. FAILURE SURFACE INCLINED TO SHEAR FORCE AT ANGLE a

b. CORRECTION OF MAXIMUM AND RESIDUAL STRENGTH FAILURE ENVELOPES

Fig. 52. Results of in situ direct shear test on specimen with inclined failure surface

99 Fig. 53 - Ideal situation where failure envelopes AB and A'B are equivalent independent of the effective i-angle

Fig. 5 *+. Decrease in strength (AB

100 discontinuity is different than that of the test surface, the failure en­ velope defining shear strength at high normal loads (line AB of fig. 44) does not necessarily apply to the entire field discontinuity. However, in most in situ tests, the effective i-angle of the test surface being influ­ enced by second-order irregularities (fig. 51b) is greater than the effective i-angle of the entire discontinuity. Therefore, line AB determined from the in situ tests will likely be a conservative estimate of the maximum strength available along the entire discontinuity. For example, if line AB (fig. 53) is determined from the tests, line A !B (fig. 53) could safely be applied to the entire discontinuity. 177. Line AB applying to the entire discontinuity can be approximated by estimating either (a) the normal stress aA , which would correspond to point A (see fig. 44) on the actual field shear strength envelope or (b) the cohesion intercept c of the true field failure envelope (see fig. 44) . If point A as determined from cr^ or the value of c are known, a line is simply drawn through A or c at an angle of 0^ , thus obtaining line AB (fig. 44). Estimation of the cohesion intercept c may be aided by future correlations of c with the joint surface geometry and internal strength of the surface irregularities. The effect of surface roughness on shear strength is being studied at the University of Karlsruhe, West Germany. Roughness is being defined in terms of the distribution of i-angles measured along the discontinuity, but at different scales (Rengers, 19 70) .

Summary of Shear Strengths

178. Failure envelopes presented in references relating to case histories were generally straight lines. Thus, for comparison of shear strengths, any raw data or curved envelopes presented in the literature were also approximated by straight lines for inclusion of Mohr-Coulomb strength parameters 0 and c in tables 1-4. The frequency distribu­ tions of 0 values for each of tables 1-4 are shown in figs. 55-58,

101 Fig. 55. Frequency distribution of $ from tests of clean discontinuities Fig. 56. Frequency distribution of 0 from tests of filled discontinuities ANGLE OF SHEAR RESISTANCE 0, DEG

Fig. 57. Frequency distribution of from tests of intact rock Fig. 58. Frequency distribution of 0 from tests of concrete blocks cast on rock surfaces respectively. Not plotted are 0 values corresponding to the residual shear stress failure criterion, and where a curved failure envelope was obtained, only the 0 corresponding to its initial portion (low normal stress) was plotted. 179. The wide range of 0 values shown in each of figs. 55-58 are due to the many types of discontinuities, intact rock, and concrete-rock contacts tested. The average of 0 and c values listed in tables 1-4 corresponding to all but the residual shear stress failure criterion are given below:

Test Zone Average ©, deg Average < Clean discontinuities 39 24 Filled discontinuities 30 23 Intact rock 50 70 Concrete on rock contacts 38 70

As expected intact specimens exhibited the greatest average shear strength and filled discontinuities the least.

106 PART V: CONCLUSIONS AND RECOMMENDATIONS

180. The type of field test most appropriate for measuring rock shear strength is the in situ direct shear test. Intact strength, dis­ continuity strength, and the strength along concrete-rock contacts can be measured. 181. The triaxial test may be the most desirable method of measuring the shear strength of a randomly jointed rock specimen, since the location of the failure surface does not have to be known. The results, however, may not be representative of the shear strength available within the entire mass, and the test is very cumbersome in comparison to the direct shear test. The torsion shear test may be useful; however, interpretation is made difficult since stresses and deformations v$ry across the specimen1s diameter. The pull-out test may possibly be used as an index to intact rock shear strength. 182. The direct shear test has a number of important advantages: a. The test can be conducted in surface trenches, underground adits, tunnels, and even calyx drill holes. b. The test is ideal for determining the shear strength of discontinuities which form potential failure surfaces. c. The shear force can be oriented in any desired direction. d. The test allows freedom of movement perpendicular to the failure surface. 183. The main disadvantage of the direct shear test is that the stress distribution across the failure surface is nonuniform and the nor­ mal stress may actually be tensile near the point of shear load applica­ tion. 184. The most important variables which affect in situ direct shear test results are: (a) test surface area or test zone volume within the test block, (b) loading procedure, (c) loading rate, and (d) moisture conditions. Portions of discontinuities, intact materials, or concrete-rock contacts tested should be characteristic of the zone or surface along which failure can occur. Specimen loading is most conveniently accomplished with hydraulic jacks acting perpendicular (normal load) and parallel (shear load) to the test surface or zone. The inclined shear load should be avoided since it can cause difficulty in interpreting test results as shown in figs. 28 and 29. Friction between the normal load mechanism and test specimen should be minimized with the use of steel roller bearings. Loading procedure, loading rate, and moisture conditions should simulate, where possible, the most critical conditions expected to occur. 185. Instrumentation should be installed to measure horizontal and vertical displacements occurring during testing. Displacement data are useful in interpreting test results. 186. Most often, Mohr failure envelopes defining the maximum and residual shear strength are desired. To determine the maximum shear strength envelope, separate specimens should be tested, each at a different normal load. Repetitive testing of a single specimen will likely yield a conservative estimate of the maximum shear strength; however, it can be used to measure the residual shear strength. 187. The shear strength measured by an in situ direct shear test is only an estimate of the true shear strength. Uncertainties in the test results dictate that caution be exercised when utilizing measured shear strengths in design. The uncertainty in the test results is caused by: a. Disturbance of the specimen during preparation. b. Unnatural stress conditions or displacements that occur during shear. c. Load and displacement measurement errors. 188. Test results must be applicable to the entire discontinuity or zone tested or to other discontinuities or zones located along potential failure surfaces. Strength measured on intact rock specimens is assumed to apply directly to other intact zones of similar material. Application of the results of tests on intact rock is aided by correlation of shear strength parameters with properties such as density, porosity, and moisture content.

108 189. The results of concrete block shear tests do give an indication of sliding resistance available beneath a concrete structure along or very near the concrete-rock contact. Test results should be applied with extreme caution since large concrete structures may Slide along discontin­ uities located at depths greater than those that can be affected by concrete block shear tests. 190. Results of discontinuity tests should be applied directly to the entire discontinuity only when the effective i-angles of the portion tested and the entire discontinuity are equivalent. Where they are not equal, the residual strength 0^ is assumed to be the same along the entire discon­ tinuity and the strength contributed by the irregularities is defined by the effective i-angle. At low normal stresses, the maximum shear strength is defined by t = an tan (0r + i) (line OA of fig. 44). 191. At high normal stresses, the maximum shear strength is defined by T = c + an tan 0r (l^ne AB of fig. 44). Ideally, the strength defined by line AB should be independent of the effective i-angles (fig. 53). However, examination of data obtained by Patton (1966a) revealed that the strength of steep teeth is reduced due to their susceptibility to progres­ sive and tensile failure (fig. 54). Thus, line AB determined for the test- surface does not necessarily apply to the entire discontinuity. However, in most in situ tests, the effective i-angle of the test surface is greater than the effective i-angle of the entire discontinuity. In that case, the strength at high normal loads determined from in situ tests can likely be considered a conservative estimate of the maximum strength available along the entire discontinuity. 192. A better estimate of line AB (fig. 44) applying to the entire discontinuity will be obtainable from future correlations of cohesion intercept c with the joint surface geometry and internal strength of the irregularities. Ultimately, a joint surface classification system should be devised in which each classification is related to a particular range of values for (0^ + i), i , or c . Classifications would essentially repre­ sent the effects of the major joint properties on shear strength. The

109 properties to be considered are (a) average joint width, (b) thickness and appropriate strength of any fill material, (c) joint surface geometry or roughness, (d) internal strength of the irregularities, (e) moisture condi­ tions and fluid pressure, and (f) proportion of intact or healed zones along the joint (i.e., the joint continuity).

110 LITERATURE CITED

1. Bieniawski, Z. T. , (1967), ’’Mechanism of Brittle Fracture of Rock,” International Journal of Rock Mechanics and Mineral Sciences, Vol 4, No. 4, October 1967, p 395. 2. Bishop, A. W. , and Henkel, D. J. , (1957), ’’The Measurement of Soil Properties in the Triaxial Test,” Edward Arnold, London, 1957, pp 125- 127. 3. Boughton, N. 0. , and Hale, G. E. A., (1967), ’’Foundation Studies for Cethana Arch Dam,” Transactions, 9th International Congress on Large Dams, Vol 1, 1967, pp 143-164. 4. Bukovansky, M . , (1966), "Three Types of Field Shear Tests on Soft Rock,” Proceedings, 1st Congress, International Society for Rock Mechanics, Vol 1, 1966, pp 343-346. 5. Clar, E. et al., (1964), "On the Practice of Rock Investigation in Austria,” Transactions, 8th International Congress on Large Dams, Vol 1, 1964, p 927. 6. Construction Ministry of the Japanese Government, (1964), "Foundation Treatment of Kawamata Dam,” Transactions, 8th International Congress on Large Dams, Vol 1, 1964, p 187. 7. Corns, C. F., and Nesbitt, R. H. , (1967), ’’Sliding Stability of Three Dams on Weak Rock Foundations,” Transactions, 9th International Con­ gress on Large Dams, Col 1, 1967, pp 463-486. 8. Coulson, J. H., (1970), "The Effects of Surface Roughness on the Shear Strength of Joints in Rock," Technical Report MRD-2-70, October 1970, Missouri River Division, U. S. Army Engineer District, Omaha, CE, Omaha, Nebraska. 9. Deere, D. R. et al., (1967), "Design of Surface and Near-Surface Construction in Rock,” Proceedings, 8th Symposium on Rock Mechanics, Minnesota, 1966, New York, 1967, AIME, pp 232-302. 10. Dodds, R, K., (1970), "Suggested Method of Test for In Situ Shear Strength of Rock,” Special Procedures for Testing Soils and Rock for Engineering Purposes, ASTM, STP 479, 1970, pp 618-628. 11. Drozd, Karel, (1967), "Variations of the Shear Strength of a Rock Mass Depending on the Displacement of the Test Blocks,” Proceedings, Geotechnique Conference, Oslo, 1967, p 265. 12. Duncan, N., (1965), "Geology and Rock Mechanics in Civil Engineering Practice,” Water Power, January 1965, pp 25-32; February 1965, pp 63-68; March 1965, pp 99-101; April 1965, pp 145-152; May 1965 pp 192-194; June 1965, pp 225-229.

Ill 13. Dvorak, A., (1957), "Field Tests of Rocks on Dam Sites," Proceedings, 4th International Conference on Soil Mechanics and Foundations Engi­ neering, Vol 1, 1957, pp 221-224. 14. Dvorak, A., and Peter, P., (1961), "Field Tests on Soils and Rocks," Proceedings, 5th International Conference on Soil Mechanics and Founda­ tions Engineering, Vol 1, 1961, pp 453-460. 15. Evdokimov, P. D,, and Sapegin, D. D., (1964), "Stability, Shear and Sliding Resistance, and Deformation of Rock Foundations," Energya, 1964, (translated from Russian by Israel Program for Scientific Trans­ lation, Jerusalem, 1967), available from U. S. Department of Commerce, Clearinghouse for Federal Scientific and Technical Information, Springfield, Va. 16. Evdokimov, P. D., and Sapegin, D. D., (1970), "A Large Scale Field Shear Test on Rock," Proceedings, 2nd Congress, International Society for Rock Mechanics, Vol. 2, Theme 3, No. 17, September 1970. 17. Gilg, B., and Dietlicher, E., (1965), "Felsmechanische Untersuchungen en der Sperrstelle Punt dal Gall," Schweizer, Bauztg, Vol 43, No. 83, 1965, pp 799-804. 18. Gole, C. V., and Makhashi, S. L . , (1970), "Some Studies on the Founda­ tion Rock of Tawa Dam (Madhya Pradesh), India," Proceedings, 2nd Congress, International Society for Rock Mechanics, Vol 2, Theme 3, No. 49, September 1970. 19. Goodman, R. E., (1969), "The Deformability of Joints," Determination of In Situ Modulus of Deformation of Rock, ASTM Winter Meeting, Committee D-18 session, STP 477, February 1969, Denver, Colo. 20. Goodman, R, E., Taylor, R. L., and Brekke, T. L., (1968), "A Model for the Mechanics of Jointed Rock," Proceedings, ASCE, Soil Mechanics and Foundations Division, Vol 94, SM3, May 1968. 21. Griffith, A. A., (1921), "The Phenomena of Rupture and Flow in Solids," Philosophical Transactions, Royal Society of London, A221, 1921, pp 163- 198. 22. Griffith, A, A., (1925), "Theory of Rupture," International Congress on Applied Mechanics, (Bienzeno and Burges, EDS.) pp 53-64, J. Waltman, Jr. Press, Delft, 1925. 23. Hartmann, B, E., (1966) "Rock Mechanics Instrumentation for Tunnel Construction," Terrametrics, Inc., Golden, Colo., 1966. 24. Haverland, M. L . , and Butler, G. L . , (1970), "Shear and Sliding Resist­ ance Tests of Rock Joints for Forebay Dam-Grand Coulee Third Powerplant Project," Report No. REC-OCE-70-6, January 1970, U. S, Bureau of Reclamation, Denver, Colo.

112 25. Hirschfeld, R. C. , Whitman, R. V., and Wolfskill, L. A., (1965), "Engi­ neering Properties of Nuclear Craters, Report 3," Technical Report No. 3-699, August 1965, U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss. 26. Horn, H. M . , and Deere, D. U., (1962), "Frictional Characteristics of Minerals," Geotechnique, Vol 12, 1962, p 319. 27. Jaeger, J. C., (1960), "Shear Failure in Anisotropic Rocks," Geological Magazine, Vol 97, No. 1, 1960. 28. James, P. M . , (1969), "In Situ Tests at Muda Dam," Proceedings, Con­ ference on In Situ Investigations in Soils and Rocks, published by British Geotechnical Society, London, 1970. 29. John, K. W , , (1961), "A Description of Full-Scale Rock Testing Based on the Example of the Work on the Kurobe IV Dam in Japan," Geologie urd Bauwesen, Vol 27, No. 1, 1961, pp 9-19. 30. John, K. W . , (1962), "An Approach to Rock Mechanics," Proceedings, ASCE, Vol 88, No. SM4, 1962, pp 1-30. 31. Kenty, J. D., and Meloy, C. R. , (1965), "Shear Evaluation of Weak Rock Foundations (ES 034) (U)," Technical Report No. 3-45, October 1965, Ohio River Division Laboratories, CE, Cincinnati, Ohio. 32. Kimishima, H., Hayashi, M . , and Kitahara, Y., (1970), "Analysis of Strain Energy of Jointed Rock Mass During Direct Shear Test in Situ," Proceedings, 2nd Congress, International Society for Rock Mechanics, Vol 2, Theme 3, No. 28, September 1970. 33. Kleiner, D. E., and Acker, R. C., (1971), "Rock Mechanics Studies for Mossyrock Arch Dam," ASCE Journal of the Power Division, Vol 97, No. P01, January 1971, p 11. 34. Krsmanovic, D., and Popovic, M . , (1966), "Large-Scale Field Tests of the Shear Strength of Limestone," Proceedings, 1st Congress, Interna­ tional Society for Rock Mechanics, Vol 1, 1966, pp 773-779. 35. Lane, K. S., (1964), "Discussion of Question 28," 8th International Congress on Large Dams, Vol 5, 1964, pp 179 and 211. 36. Link, H., (1969), "The Sliding Stability of Dams--Parts I, II, and III," Water Power, March-May, 1969. 37. Locher, H. G., and Rieder, G. U., (1970), "Shear Tests on Layered Jurassic Limestone," Proceedings, 2nd Congress, International Society for Rock Mechanics, Vol 2, Theme 3, No. 1, September 1970. 38. Lorente, Carlos, (1968), "Elasto-Plastic Stress-Strain Distribution During "In Situ" Shear Tests," Proceedings, International Symposium on Rock Mechanics, 1968, p 183.

113 39. Maddox, J. M. , Kinstler, F. L. , and Mather, R. P. , (1967a), "Meadowbank Dam--Foundations,M Civil Engineering Transactions, Vol CE9, No. 2, October 1967, The Institution of Engineers, Sydney, Australia. 40. Maddox, J. M . , Kinstler, F. L . , and Mather, R. P., (1967b), "Foundation Studies for Meadowbank Buttress Dam," Transactions, 9th International Congress on Large Dams, Vol 1, 1967, pp 123-141. 41. Maurer, W. C., (1965), "Shear Failure of Rock Under Compression," Journal, Society of Petroleum Engineers, Vol 5, No. 2, 1965, pp 167-176. 42. Mizukoshi, T., Tanaka, H., and Inouye, Y., (1967), "A Geologic Investi­ gation on the Stability of Reservoir Banks," Transactions, 9th Inter­ national Congress on Large Dams, Vol 1, 1967, p 47. 43. Morgenstern, N. R., and Tchalenko, J. S., (1967), "Microscopic Struc­ tures in Kaolin Subjected to Direct Shear," Geotechnique, Vol 17, 1967, pp 309-328. 44. Muller, L. , (1961), "Basic Facts Concerning Full-Scale Tests in the Field of Rock Technology," Geologie und Bauwesen, Vol 27, No. 1, 1961, pp 3-8. 45. Muller, L., and John, K. W . , (1963), "Recent Development of Stability Studies of Steep Rock Slopes in Europe," Transactions, Society of Mining Engineers, September 1963. 46. Multipurpose Dam Rock Testing Group, (1964) , "Rock Tests in Multipur­ pose Dams in Japan," Transactions, 8th International Congress on Large Dams, Vol IV, 1964, pp 715-752. 47. Niederhoff, A. E., (1939), "Field Tests of a Shale Foundation," Pro­ ceedings, ASCE, Vol 65, 1939, pp 1239-1254. 48. Nose, M . , (1964), "Rock Test In-Situ, Conventional Tests on Rock Properties and Design of Kurobegawa Dam Based Thereon," Transactions, 8th International Congress on Large Dams, Vol 1, 1964, pp 219-252. 49. Patton, F. D., (1966a), "Multiple Modes of Shear Failure in Rock and Related Materials," Ph.D Thesis, University of Illinois, 1966, p 282. 50. Patton, F. D., (1966b), "Multiple Modes of Shear Failure in Rock," 1st Congress, International Society for Rock Mechanics, Vol 1, 1966, p 509. 51. Pigot, C. H., and MacKenzie, I. D., (1961), "Carillon Foundation Studies," The Engineering Journal, October 1961, pp 65-71. 52. Pigot, C. H., and MacKenzie, I. D., (1964), "A Method Used for In Situ Bedrock Shear Tests," Transactions, 8th International Congress on Large Dams, Vol 1, 1964, pp 495-511.

114 53. Rengers, Niek, (19 70), !,Influence of Surface Roughness on the Fric­ tion Properties of Rock Planes," Proceedings, 2nd Congress, Interna­ tional Society for Rock Mechanics, Vol 1, Theme 1, No. 31, September 21-26, 1970. 54. Rocha, M . , (1964a), "Mechanical Behavior of Rock Foundations in Concrete Dams," Transactions, 8th International Congress on Large Dams, Vol 1, 1964, pp 785-832. 55. Rocha, M . , (1964b), "Discussion of Question No. 28," Transactions, 8th International Congress on Large Dams, Vol 5, 1964, p 207. 56. Rocha, M. et al., (1967), "Influence of a Very High Deformability of the Foundation on the Conception and Behavior of an Arch Dam," Trans­ actions, 9th International Congress on Large Dams, Vol 1, 1967, p 441. 57. Rountree, J. R., (1940), "Discussion of Field Tests of a Shale Founda- tion," Proceedings, ASCE, Vol 66, 1940, pp 1217-1222. 58. Ruiz, M, D., and Camargo, F. P., (1966), "A Large Scale Field Shear Test on Rock," Proceedings, 1st Congress, International Society for Rock Mechanics, Vol 1, 1966, pp 257-262. 59. Ruiz, M. D. et al., (1968), "Some Consideration Regarding the Shear Strength of Rock Masses," Proceedings, International Symposium on Rock Mechanics, Madrid, 1968, p 159. 60. Salas, J., and Uriel, S., (1964), "Some Recent Rock Mechanics Testing in Spain," Transactions, 8th International Congress on Large Dams, Vol 1, 1964, pp 995-1021. 61. Sarmento, G., and Vaz, L., (1964), "Cambambe Dam Problems Posed by the Foundation Ground and Their Solution," Transactions, 8th International Congress on Large Dams, Vol 1, 1964, pp 443-464. 62. Scott, K. F., Reeve, W. T. N., and Germond, J. P., (1968), "Farahnaz Pahlavi Dam at Latujan," Proceedings, Institute of Civil Engineers, Vol 39, March 1968, pp 353-395. 63. Serafim, J. L . , (1964), "Rock Mechanics Considerations in the Design of Concrete Dams," State of Stress in the Earthfs Crust, W. R. Judd, Editor, 1964, pp 611-644. 64. Serafim, J. L. and Folque, J. B., (1957), Discussion of "Techniques of Field Measurement and Sampling," Proceedings, 4th International Con­ ference on Soil Mechanics and Foundation Engineering, Vol III, 1957, pp 121-122. 65. Serafim, J. L., and Guerriero, M . , (1966), "In Situ Tests for the Study of Rock Foundations of Concrete Dams," First Congress, International Society for Rock Mechanics, 1966, Vol II, pp 549-556.

115 66. Serafim, J. L. and Guerriero, M . , (1968), "Shear Strength of Rock Masses at Three Spanish Dam Sites," Proceedings, International Symposium on Rock Mechanics, Madrid, 1968, p 147. 67. Serafim, J. L. and Lopes, J. J. B., (1961), "In Situ Shear Tests and Triaxial Tests of Foundations of Concrete Dams," Proceedings, 5th International Conference on Soil Mechanics and Foundation Engineering, Vol 1, 1961, pp 533-539. 68. Steinbichler, H., (1961), "Instruments and Equipment Used for Full-Scale Rock Tests," Geologie und Bauwesen, Vol 27, No. 1, 1961, pp 20-28. 69. Tchalenko, J. S., (1970), "Similarities Between Shear Zones of Different Magnitudes," Geological Society of America Bulletin, Vol 81, June 1970, pp 1625-1640. 70. Thorfinnson, S. T., (1954), "A Large Scale Field Shear Test on a Bentonite Seam," Proceedings, ASCE, Vol 80, Separate 549, 1954, pp 1-27. 71. U. S. Army Engineer District, CE, Fort Worth, (1961), "Report on Field Shear Tests, Proctor Reservoir, Leon River, Texas," U. S. Army Engineer District, Fort Worth, Texas, August 1961. 72. U. S. Bureau of Reclamation, (1965), "Morrow Point Dam and Powerplant Foundation Investigation," Water Resources Technical Publication, U. S. Department of the Interior, Bureau of Reclamation, Denver, Colo., October 1965. 73. Underwood, L. B., (1964), "Chalk Foundations at Four Major Dams in the Missouri River Basin," Transactions, 8th International Congress on Large Dams, Vol 1, 1964, pp 23-48. 74. Uriel, Romero S., (1966), "An In Situ Direct Shear Test with Saturation of the Rocks and Interpretation of the Great Shear Test in the Nature," Proceedings, 1st Congress, International Society for Rock Mechanics, Vol 1, 1966, pp 353-358. 75. Uriel, Romero S., (1968), "In Situ Direct Shear Tests on Irregular Surface Joints Filled with Clayey Material," Proceedings, International Symposium on Rock Mechanics, Madrid, 1968, p 189. 76. Wallace, G. B., Slebir, E. J., and Anderson, F. A., (1970), "Founda­ tion Testing at Auburn Dam," Proceedings, 11th Symposium on Rock Mechanics, University of California, Berkeley, Calif., June 1969, W. H. Somerton, Editor, American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., Publishers, 1970. 77. Wilson, S. D., and Maraño, D., (1968), "Performance of Muddy Run Embankment," Proceedings, ASCE Journal of Soil Mechanics and Founda­ tions Division, Vol 94, No. SM4, July 1968, pp 859-881.

116 SELECTED BIBLIOGRAPHY

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117 14. Krsmanovic, D. and Langof, Z. (1964) , ’’Large Scale Laboratory Tests of the Shear Strength of Rocky Material,” Rock Mechanics and Engineering Geology, Supplement 1, 1964, pp 20-29. 15. Lajtai, E. Z. , (1969a), ’’Strength of Discontinuous Rocks in Direct Shear,” Geotechnique, Vol 19, No. 2, 1969, pp 218-233. 16. Lajtai, E. Z. (1969b), ’’Shear Strength of Weakness Planes in Rock,” International Journal of Rock Mechanics and Mineral Sciences, Vol 6, 1969, pp 499-515. 17. Lundborg, N. (1968), ’’Strength of Rock Like Materials,” International Journal of Rock Mechanics and Mineral Sciences, Vol 5, No. 5, Septem­ ber 1968. 18. Muller, L. (1959), "The European Approach to Slope Stability Problems in Open - Pit Mines,” Colorado School of Mines Quarterly, Vol 54, No. 3, July 1959, pp 115-133. 19. Muller, L. (1961), ’’Safety of Rock Abutments on Concrete Dams,” Transactions, 7th International Congress on Large Dams, Rome, Vol II, 1961, p 663. 20. Muller, L. (1964a), ’’The Stability of Rock Bank Slopes and the Effect of Rock Water on Same,” International Journal of Rock Mechanics and Mineral Sciences, Vol 1, No. 4, 1964, pp 475-504. 21. Muller, L. (1964b), ’’Application of Rock Mechanics in the Design of Rock Slopes,” State of Stress in the Earth’s Crust, W. R. Judd, Editor, Santa Monica, Elsevier Publishing Company, New York, 1964, pp 575-606. 22. Oberte, G. and Rebaudi, A. (1967), ’’Bedrock Stability Behavior with Arch-Gravity Dam,” Transactions, 9th International Congress on Large Dams, Vol 1, September 1967, p 849. 23. Pacher, F. (1961), ’’Evaluation of Full Scale Tests,” Geologie und Bauwesen, Vol 27, No. 1, 1961, pp 29-32. 24. Peironcely, J. M. and Sanz Saracho, J. M. (1966), "A Rapid Method for Determining the Bearing Capacity of a Soil,” Proceedings, 1st Congress, International Society for Rock Mechanics, Vol 1, 1966, pp 693-695. 25. Rawlings, G. E. (1968), ’’Stabilization of Potential Rock Slides in Folded Quartzite in Northwestern Tasmania,” Engineering Geology, Vol 2, No. 5, 1968, pp 283-292. 26. Ringheim, A. S. (1964), "Experiences with the Bearpaw Shale at the South Saskatchewan River Dam,” Transactions, 8th International Congress on Large Dams, Vol 1, 1964, p 529. 27. Ripley, C. F. and Lee, K. L. (1961) , ’’Sliding Friction Tests on Sedi­ mentary Rock Specimens,” Communication 8, Transactions, 7th International Congress on Large Dams, Vol 4, 1961, pp 657-671.

118 28. Rosa, S. A. et al. (1964), "Studies of Deformation Properties of Rock Foundations of High Arch and Gravity Dams in the USSR," Proceedings, 8th International Congress on Large Dams, Vol 1, 1964, p 1023. 29. Rosenblad, J. L. (1971), "Geomechanical Model Study of the Failure Modes of Jointed Rock Mass," Technical Report MRD-1-71, Missouri River Division, January 1971, U. S. Army Engineer District, Omaha, Nebraska. 30. Sellers, J. B. (1968), "Rock Mechanics Instrumentation in Tunnels," Water Power, July 1968. 31. Serafim, J, L. (1964a), "The Behavior of Arch Dams and Their Founda­ tion," Water Power, May 1964, p 199. 32. Serafim, J. L. (1964b), "Discussion of Question 28," Transactions, 8th International Congress on Large Dams, Vol 5, 1964, p 201. 33. Sherman, W. G. (1968), "Survey of Slope Failures in Reservoirs," Miscellaneous Paper No. 3-981, 1968, U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss. 34. Skempton, (1964), "The Long Term Stability of Clay Slopes," Geotechnique, Vol 14, June 1964. 35. Terzaghi, K. T. (1962), "Stability of Steep Slopes on Hard Unweathered Rock," Geotechnique, Vol 12, 1962, pp 251-270. 36. Thomas, H. H. (1964), "Discussion of Question No. 28," Transactions, 8th International Congress on Large Dams, Vol 5, 1964, p 221. 37. U. S. Army Engineer District, Omaha, (1966), "Strength Parameters of Selected Intermediate Quality Rocks," Engineering Study No. 552, Rock Mechanics Investigations, First Interim Report, Missouri Research Division Laboratory, U. S. Army Engineer District, Omaha, Nebraska, July 1966. 38. Uriel, S. (1964), "Discussion of Question 28," Transactions, 8th International Congress on Large Dams, Vol 5, 1964, p 217. 39. Wallace, G. B. and Olsen, 0. J. (1966), "Foundation Testing Techniques for Arch Dams and Underground Powerplants," ASTM-STP402, Philadelphia, Pa. 1966. 40. Wisecarver, D. W. et al. (1964), "Investigation of In-Situ Rock Stresses, Ruth Mining District, Nevada, with Emphasis on Slope Design Problems in Open-Pit Mines," U. S. Bureau of Mines, R. I. 6541, 1964. 41. Withers, J. H. (1964), "Sliding Resistance Along Discontinuities in Rock Mass," Ph.D Thesis, University of Illinois, 1964.

119 Table 1

Data from Tests of Clean Discontinuities

Case History (as numbered in Specimen Shear Strength^ Moisture Appendixes A and E) Height Base Area Description of Discontinuity 0 (deg) c (psi) Failure Criterion Conditions Remarks ^ ^ ^ „(3) A-l ... 32 sq ft Bedding planes in limestone: Block 1 ...... Block 2 ::: ...... i 2 ) A-2 15 ft 32k sq ft Basalt-sandstone contact Dilatance ... ) = assuming c = 0. Single specimen. Displacement : O.Ol* in. ... 0 = k k y by assuming c = 0. Single specimen.

A-3 8 in. 1.6 sq ft Mica-schist sheared parallel to the foliation: Block 1 and 2 Maximum shear stress — 0 = 6 8 ^ \ c = 0. Block 1 28{ l \ . . . Maximum shear stress — — Block 2 < — Maximum shear stress — First three tests. Block 2 35l ; Maximum shear stress ... Last three tests.

E-l ... 2.8 sq ft Smooth joint in quartzite 2 k 25 ... Wet Repetitive testing apparently was used to obtain shear strength. f 2 ) E-2 ... 3.2 to 8.6 sq ft Clean bedding plane in greywacke Maximum shear stress Submerged 0 = 30' , c = ll*. Single specimen. Initial test yielded similar strength. Schistosity plane in amphibolite Maximum shear stress Submerged 0 = 1*6'^', c = 0. Single specimen. Initial test yielded greater strength. Fissure plane in gneiss Maximum shear stress Submerged 0 = 1*6'^', c = 25. Single specimen. Initial test yielded similar strength. Schistosity plane in chlorite schist Maximum shear stress Submerged 0 = 10(2), c = 7« Single specimen. Initial test yielded similar strength.

E-i+ 1 ft 3 sq ft Sandstone-shale contact 32 10 Bedding plane in sandstone k2 8 ::: Discontinuous bedding plane in 53 b2 ::: sandstone (2) E-5 8 in. 1.6 sq ft Tight joint in granite 1*0/?\ bk Maximum shear stress Single specimen. Initial test, yielded, similar strength. Very tight discontinuous joint in granite 36V 19 Maximum shear stress ___ Single specimen. Initial test yielded much higher shear strength.' 28(3) E-8 10 in. 1.0 sq ft Indurated clay 25 Maximum shear stress Natural Shear usually occurred along randomly oriented slickensides; however, for some specimens, shear took place through portions of intact material.

E-9 10 in. 1.0 sq ft Indurated clay, more dense than that 1*0^ :> 20 Maximum shear stress Natural Shear usually occurred along randomly oriented slickensides; of case history E-8. however, for some specimens, shear took place through portions of intact material. Claystone with horizontal slickensides ^3(3) 0 Maximum shear stress Natural Shear occurred along the slickensides. spaced at l/8 in. or less.

E-10 10 in. 1.0 sq ft Highly fissile calcareous shale li*<3> bo Maximum shear stress Natural Shear occurred along the laminations, containing horizontal laminations. f 2 ) E-ll ... 5U sq ft Clean joint in limestone Maximum shear stress — 0 = 37^ , c = 112. Strength at normal stress = 30 to 350 psi.

1*2(3) E-13 ... 5-3 sq ft Vesicular basalt, amygdaloidal basalt, 26 to 3^ Maximum shear stress — Shear apparently occurred along interconnecting joints. Test and jointed basalt. results of the three types of rocks were combined in determining shear strength parameters.

E-15 ... 5-3 sq ft Schistosity plane i*q (3) 10 Maximum shear stress — (2) E-17 8 in. 1.6 sq ft Foliation surface in amphibolite Maximum shear stress ___ S = 1*1' , c = 80. Single specimen was tested, Initial test yielded a much higher shear strength.

NOTE: (l) Strength parameters are those presented in references; those stated in remarks were interpreted for this report. (2) Strength parameters determined from results of repetitive testing of one or a number of specimens at various normal loads. (3) Strength parameters determined from results of one test on each specimen or the initial test on each specimen where repetitive testing was used. Data from Tests of Filled Discontinuities

Case History ,, ( 1 ) (as numbered in Specim en S h ea r S t r e n g t h ' M o is tu re Appendixes B and E) Height Base Area Description of Discontinuity 0 (d e g ) c ( p s i) Failure Criterion C o n d itio n s Remarks

B - l 19 ft 529 sq ft Discontinuity in diabase filled with Maximum sh e a r s t r e s s ___ f = 56^ assum ing c = 0 . S in g le sp e cim e n . chlorite and serpentine

B-2 23 ft 1000 sq ft Heavily jointed granite: B lo c k 1 (ungrouted) U s(2 ) 37 Maximum sh e a r s t r e s s Failure took place along interconnecting joints apparently B lo c k 2 ( g ro u te d ) f a ) 37 Maximum sh e a r s t r e s s containing varying amounts of fill material. Each block was resheared once.

B-3 2 ft U sq ft Mudstone seams in quartzite: (l) weathered seam 2 0 (2 ) 12 Maximum sh e a r s t r e s s Wet Twice resheared. ? g ( 2 ) (2) slightly weathered seam 6 Maximum sh e ar s t r e s s Wet Twice resheared. (3) unweathered seam o g ( 2 ) 2 Maximum s h e a r s t r e s s Wet Twice resheared. 6 (2 ) (4 ) above three types 19V ' 1 t o 6 Maximum s h e a r s t r e s s Wet Blocks resheared several times to attain residual strength.

B-U 1 .5 f t 7 sq f t Breccia zone in mudstone containing clayey silt and a few rock fragments: S e r ie s A 2 N a t u r a l Free drainage. f a ) S e r ie s B 1 — N a t u r a l Slower rate of shearing than tests of Series A. f a ) Plastic clay seam in sandstone 1 — N a t u r a l Slow t e s t . i k ( 3 ) B-5 ---- 6.25 sq ft A ltered zone in shale (3/8 in. thick) 6 Maximum sh e a r s t r e s s N a tu r a l In itial peak in shear stress versus displacement plot. 3 Displacement: 2 .0 in . N a t u r a l —

B-6 1 1 sq f t Filled bedding planes in limestone: Test Series I: clay filled (thick) 28 ( 3 ) 9-6 Maximum sh e a r s t r e s s N a tu r a l Interlocking along joint contact occurred. 3 8 ( J Test Series II: clay and grout filled 3 l l . l Maximum sh e a r s t r e s s — Interlocking along joint contact occurred. ( t h ic k ) o , ( ) Test Series III: clay filled (thin) 3 116 Maximum sh e ar s t r e s s ___ Interlocking along joint contact occurred. Test Series IV: clay filled (thin) i f a 78 Maximum sh e a r s t r e s s Interlocking along joint contact occurred. fo) B-7 375 sq f t Contact between compact basalt and Maximum sh e a r s t r e s s S a tu r a te d f = 68^-)/by assuming c = 0 . Single specimen. Specimen was basaltic breccia. The contact was resheared in a direction 90 deg to that of the in itial test indicated to be a zone of fractured rock resulting in a reduced measured strength.

B-8 ---- 2.7 to 10.8 sq ft T hin and slightly irregular lignite ’ 3 k > 10 — — — layer in limestone.

B-9 3.3 ft 169 sq ft Same as tested in case history (B-8) — — — — Single specimen. Results plotted slightly below Mohr-Coulomb envelope determined in case history (B-8).

1 7 ( 3 ) B-10 2.5 ft J+7 sq ft Bentonite seam in chalk (l /2 in. thick) 1 7 — N a tu r a l Two specimens were tested. 8 (3 ) B- 11 3 f t 6 .3 s q f t Bentonite seam in chalk (max.thickness 2 — — — = 3 i n . ) .

E - l ---- 2 .8 sq f t B edding plane shear zone in quartzite 23 8 ___ Wet Repetitive testing was apparently used. (l in. thick). Bedding plane shear zone in quartzite 36 75 ___ Wet Repetitive testing was apparently used. ( 0.4 in. thick). f 2) E-2 --- 3*2 to 8.6 sq ft Clay filled bedding plane in greywacke Maximum s h e a r s t r e s s Subm erged / = 2 3 v , c = 0 . Single specimen. Initial test yielded less filled with clay of 0.1 in. thickness strength due to better contact or greater effective normal stress during repetitive testing. (Continued)

NOTE: (l) Strength parameters are those presented in references; those stated in remarks were interpreted for this report. (2 ) Strength parameters determined from results of repetitive testing of one or a number of specimens at various normal loads. (3 ) Strength parameters determined from results of one test on each specimen or the in itia l test on each specimen where repetitive testing was used. Table 2 (Concluded)

Data from Tests of Filled Discontinuities

Case History (as numbered in Specimen Shear Stre n g t h ^ Moisture Appendixes B and E) Height Base Area Description of Discontinuity 0 (deg) c (psi) Failure Criterion Conditions Remarks^

8 in. 1.6 sq ft Clay filled joint in granite: Block 1 2U* (2) 3 18 Maximum shear stress E-5 2 J 2 ) — Initial test yielded similar strength. Block 2 18 Maximum shear stress Initial test yielded similar strength.

E-6 5 ft 32 sq ft Discontinuity in biotite granite filled Maximum shear stress Saturated 0 = 1+7, c = 0. Two specimens were tested. with 0.2 in. of loose sandy material

E-ll 5I* sq ft Discontinuities in limestone: (1) filled with detritic material Maximum shear stress ___ 0 = c = 28. Strength for normal stress = 20 to 350 psi. (0.01+ in. thick) (2) clay filled (up to 0.8 in. thick) Maximum shear stress — 0 = 15' , c = ll+. Strength for normal stress = 20 to 350 psi. 28 (3) E-12 3 sq ft Joints in marl filled with fibrous 23 — Saturated — gypsum (l to 1* in. thick). 29(3 ) Joints in marl filled with fibrous 21 — Natural — gypsum (l to U in. thick).

E-ll* 5.3 sq ft Joint in quartzite partially filled 1*1^3) 0 Maximum shear stress Natural — with clay. 3l(3) Joint in quartzite completely filled 0 Maximum shear stress Natural — with clay

E-15 ___ 5-3 sq ft Clay filled joints in schist 38(3) 1+6 Maximum shear stress

NOTE: (l) Strength parameters are those presented in references; those stated in remarks were interpreted for this report. (2) Strength parameters determined from results of repetitive testing of one or a number of specimens at various normal loads. (3) Strength parameters determined from results of one test on each specimen or the initial test on each specimen where repetitive testing was used. Table 3

Data from Tests of Intact Rock Specimens

Case History (as numbered in Specimen Shear Strength^ ^ Moisture Appendixes C and E) Height Base Area Description of Material 0 (deg) c (psi) Failure Criterion Conditions Remarks

C-l 6-8 in . 2.7 to IO.7 sq ft Claystone ...... Test data not available. ____ 6-8 in . k.2 sq ft Claystone Natural Test data not available. 22(3) C-2 10 in. 1 sq ft Calcero-argillaceous marl 55 Maximum shear stress Natural ...

„ ( 3 ) C-3 ... Amygdaloidal andesite 86 Maximum shear stress -- Amygdaloidal andesite 52 0 Residual shear stress -- This strength was termed the sliding or residual strength. criterion was likely used.

C-U 1 ft 5.3 sq ft Granite displaying variable and 35-60^3) 0-182 Maximum shear stress Saturated The strength was dependent on the rock quality. Strength sometimes very intense alteration and dilatance determined by the dilatance criterion was slightly less than that corresponding to the maximum shear stress criterion.

C-5 5.3 sq ft Sandstone, vesicular basalt, and i 4 o Maximum shear stress Test results of the three types of rocks were combined in sandstone basalt breccia g » ) 50 Dilatance ::: determining shear strength parameters. > 100 Displacement of O.Ot- in

c-6 1.2 ft 5-3 sq ft Altered granite U o ... Strength at normal stresses < 71 psi. Altered granite 22U' \k2 ... Strength at normal stresses > 71 psi.

(2 ) E-2 — 3 .2-8.6 sq ft Slightly weathered amphibolite Maximum shear stress Submerged 0 = 63/2 \, c = 18. One specimen of each rock type was tested. Mica-schist gneiss Maximum shear stress Submerged 0 = 57' , c = 70. Initial test on each specimen yielded similar strength.

E-4 1 ft 3 sq ft Sandstone 60 iho ......

(3 ) E-6 6 ft 9^ sq ft Jointed and faulted biotite granite Maximum shear stress Saturated 0 = 78' , c = l60. Two specimens were tested. Shear may have occurred partially through intact rock and partially along existing discontinuities.

E-7 2.5-3.3 :ft 22-28 sq ft Liparite containing randomly Maximum shear stress 0 = 6 8 ^ by assuming c = 0. Four specimens were tested at oriented joints approximately the same normal stress and failed at approximately the same shear stress. Shear likely took place through intact rock and partially along existing discontinuities.

E-10 10 in. 1 sq ft Calcareous shale (highly fissile) i - j . 0 ) 50 Maximum shear stress Natural Specimens were sheared perpendicular to the bedding.

E-12 3 sq ft Calcareous marl 26-62 ... Saturated 369 ? i3> Argillaceous marl 10 Saturated ::: Argillaceous marl' 51 Natural 53(3) E-lU ... 5-3 sq ft Quartzite containing joints 90 Maximum shear stress Natural Specimens were sheared perpendicular to the joints.

lh(3) E-l6 1 ft 9 sq ft Hard shale containing iron concretions i i + Maximum shear stress Submerged

Hard shale containing iron concretions 1 U . 5 ( 3 ) 6 Residual shear stress Submerged Residual stress was actually not attained in any of the tests.

NOTE: (l) Strength parameters are those presented in references; those stated in remarks were interpreted for this report. (2) Strength parameters determined from results of repetitive testing of one or a number of specimens at various normal loads. (3 ) Strength parameters determined from results of one test on each specimen or the initial test on each specimen where repetitive testing was used. Table k

Data from Tests of Concrete Blocks Cast on Rock Surfaces

Case History (as numbered in Specimen Shear Strength^ Moisture ( 1 ) Appendixes D and E) Height Base Area Description of Surface 0 (deg) c (psi) Failure Criterion Conditions Remarks

D-l 1.6 ft 5‘b sq ft Sandstone 30(3) 13.5 Shear occurred within rock beneath contact.

D-2 11 and UM sq ft Compact diabase 170 Maximum shear stress Submerged Location of failure surface varied. 38(* 232) Compact diabase 66 Maximum shear stress Submerged Location of failure surface varied. Heavily fractured diabase 31 19.6 Maximum shear stress Submerged Shear occurred within rock beneath contact. 33^$ ; Heavily fractured diabase 18.3 Maximum shear stress Submerged Shear occurred within rock beneath contact. o(3) D-3 — 1 sq ft Prepared clay shale 9 Maximum shear stress Shear occurred within rock beneath contact, Prepared clay shale 0(3 ) 17 Residual shear stress Shear occurred within rock beneath contact.

D-1+ 5 in. 1 sq ft Layer of grout placed before concrete: Previously sheared claystone 3^1 25 Maximum shear stress Shear of bond, grout, and rock occurred. Previously sheared calcareous shale 0 Maximum shear stress Shear of bond, grout, and rock occurred. Previously sheared marl (test blocks 30 Maximum shear stress Shear occurred mainly along grout-marl contact. entirely of grout)

D-5 Previously sheared limestone Maximum shear stress 0 = 65/p\> c = 0. Strength at normal stresses < 70 psi. 0 = 35' , c = 11. Strength at normal stresses > 70 psi.

D-6 1.2 ft 3.8 sq ft Jointed diabase and tuff Strength parameters could not be determined from the scattered data.

D-7 5 ft 25 sq ft Fine grained shale Maximum shear stress Natural 0 = 36'° , c = 8. Two specimens tested and shear took place along-aoncrete-shale contact. Fine grained shale Maximum shear stress Natural 0 = 38' J by assuming c = 0. Single specimen. Shear occurred in rock beneath concrete. oo(3) d -8 k.5 ft 15 sq ft Laminated shale 13 Maximum shear stress Shear occurred within rock directly below the; concrete-rock Laminated shale 0 Maximum shear stress — contact. „(3) d -9 — — Medium grained sandstone ik _ _ _ Fine grained sandstone 7 Clay shale $ 3 ] 28

D-10 3 ft 17.5 sq ft — — — Maximum shear stress Data insufficient for determination of shear strength parameters.

D-ll — 5.3 sq ft Clean limestone surface 6i<3 > 80 Maximum shear stress Shear occurred either along concrete-rock contact or partially along contact and through rock. Limestone covered with thin clay film W < 3) 25 Maximum shear stress Shear occurred only along concrete-rock contact. (2 ) j E-2 — 3.2 to 8.6 sq ft Greywacke Maximum shear stress 0 = 39' , c = k-2. Single specimen. Initial! test yielded a much greater strength.

... to 10 sq ft Granulite ,fi(2) E-3 2.5 3°(2) 1U2 — Gneiss 35^ ' ill

E-l| 1 ft 3 sq ft Sandstone Ml 71

(3) E-6 6.2 ft 100 sq ft Biotite granite Maximum shear stress Satruated = U5' , c = 180. Shear occurred within the rock directly beneath the concrete-rock contact.

E-16 1 ft 9 sq ft Hard shale iu Maximum shear stress Submerged Shear occurred in shale directly beneath the concrete-rock Hard shale 11 Residual shear stress Submerged contact.

NOTE: (l) Strength parameters are those presented in references; those stated in remarks were interpreted for this report. (2) Strength parameters determined from results of repetitive testing of one or a number of specimens at various normal loads. (3) Strength parameters determined from results of one test on each specimen or the initial test on each specimen where repetitive testing was used. APPENDIX A

CASE HISTORIES INVOLVING TESTS OF CLEAN DISCONTINUITIES CASE HISTORY NO. A-l

1. Reference. Locher and Reider (1970)*

2. Project. Slope stabilization adjacent to a road cut.

3. Purpose. To obtain shear strength along joints.

4. Location of Test on Project Site. Tests were carried out on a quarry- slope located near a slide area.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested, Two limestone blocks resting on clean bedding planes were tested. Blocks were formed by cutting lateral trenches down to the bedding plane. Cutting was carried out with pneumatic hammers. During preparation the proposed block was stabilized by placing a rock anchor through and perpendicular to the blockfs upper surface. The anchor was also placed slightly off center to compensate for the overturning mo­ ment that would be produced by the horizontal shear load. The test surface area was approximately 32 sq ft.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Criteria. The horizontal shear load was applied with a hydraulic jack. The normal load was produced by stressing the rock anchor. After choosing a normal load, the shear load was increased in increments until appreciable sliding occurred. The shear load was then released and the block resheared under different normal loads. Vertical and horizontal displacements were measured during shear.

7. Test Results, Conclusions, and Comments. Values of 0 were presented:

Block 0, deg 1 50 2 52

After completing the tests, a layer of loose material was found along the joint surfaces. Laboratory direct shear tests on smaller specimens resulted in slightly lower shear strengths.

References for this appendix are included in the list of literature cited, which follows the main text.

A1 CASE HISTORY NO. A-2

1. Reference. Ruiz and Camargo (1966)

2. Project. Jupia Dam on the Parana River, Brazil. Tests were conducted by LNEC, Portugal.

3. Purpose. To obtain the shear resistance in areas where it was difficult to form small-scale blocks without excessively disturbing the test surface.

4. Location of Test on Project Site. No information.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The unbonded contact between a microcrystalline compact basalt block and a thin layer of sandstone was tested. The test block was 15 ft high with base dimensions by 18 by 18 ft (area = 324 sq ft) and was formed by hand-held tools. Explosives were avoided to prevent disturbance of the basalt-sandstone contact. The basalt block was left exposed during testing.

6. Test Conditions, Loading Procedures, Rate of Loading, and Failure Criteria. The normal load was produced by only the block1s weight and was equal to 18 psi. The horizontal shear load was applied in loading and unloading cycles by three hydraulic jacks of 900-metric-ton total capacity. During each load cycle, the horizontal force was kept constant until no further displacement was observed. Nine gages were used to measure vertical displacement and ten were used to measure horizontal displacement.

Failure criteria: (1) Dilatance criterion: shear stress at which vertical displacement changes from downward to upward; (2) Displace­ ment criterion: shear stress at the horizontal displacement of 0.04 in.

7. Test Results, Conclusions, and Comments. The maximum shear strength available was never attained; however by assuming c = 0, a value for 0 can be computed for each of the above failure criteria and for each loading cycle. Results of the first four load cycles were presented as follows:

A2 Dilatance Criteria 0,04-in. Displacement Shear Stress 0 Shear Stress 0 Cycle psi deg psi deg i 11.0 31 14.6 39 2 9.6 28 15.6 41 3 14.0 38 20.0 48 4 12.6 35 21.0 49 Avg 34 44

The test block did not deform uniformly, instead greater horizontal and vertical displacements occurred near the point of shear load appli­ cation. The maximum horizontal and vertical displacements presented were 0.06 and 0.1 in., respectively.

A3 CASE HISTORY NO. A-3

1. Reference. U. S. Bureau of Reclamation (1965)

2. Project. Morrow Point Dam and Power Plant, Colorado

3. Purpose. To determine foundation shear strength.

4. Location of Test on Project Site. Tests were conducted inside the underground power plant exploratory tunnel.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Two blocks of mica-schist were sheared parallel to the folia­ tion. The blocks were prepared by line drilling followed by chipping and bushhammering down to the desired size of 8 in. high with a 15 by 15 in. base (area = 1.56 sq ft). Each specimen was encased in a steel frame.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Criteria. The normal and shear loads were applied with hydraulic jacks. The nor­ mal stress of 400 psi was considered to be representative of the load to be exerted by the dam. The normal stress was applied followed by incremental application of the inclined shear stress. The normal load was kept constant by reducing the vertical load by an amount equal to the normal component of the inclined shear load. Horizontal and vertical displacements were measured with dial gages capable of reading directly to the nearest 0.001 in. After initial failure, the blocks were re­ sheared at various normal loads and moisture conditions. The maximum shear stress failure criterion was employed with the failure shear stress being the maximum shear stress which could be mobilized.

7. Test Results, Conclusions, and Comments.

Initial failure

Block 1: the normal stress was 400 psi with shear failure at 917 psi.

Block 2: the normal stress was 600 psi with shear failure at 1511 psi. By assuming c = 0, 0 is found to be approximately 68 deg.

The failure surfaces were irregular. Displacements at failure were 0.045 in. in shear direction and 0.02 in. upwards for block 1 and 0.095 in. in shear direction and 0.04 in. upwards for block 2. Inversion from downward to upward displacement occurred at a shear stress of approxi­ mately 1/2 the maximum shear resistance.

A4 Repetitive testing

After initial failure, blocks 1 and 2 were resheared. The sequence of normal stresses was 600, 400, 600 and 400 psi for block 1 and 800, 600, 400, 800, 600, and 400 psi for block 2. The shear resistance along both failure surfaces had reduced considerably after initial failure. The reshearing of block 1 yielded a 0 of 28 deg. The shear strength measured in the last test on block 1 at a normal stress of 400 psi was not used to determine 0, since the steel frame around the block scraped along the rock surface during shear. The reshearing of block 2 yielded a 0 of 48 deg corresponding to the first three tests and a 0 of 35 deg corresponding to the final three tests.

Laboratory direct shear tests were conducted on two blocks of the same rock type and size of blocks 1 and 2 tested in the field. The normal stress at failure for each block was 400 psi and corresponding shear failure stress was about 1100 psi. Reshearing of the laboratory speci­ mens yielded results similar to those obtained in the field reshearing tests.

Laboratory triaxial tests were also conducted on NX-size core speci­ mens. Field and laboratory direct shear results were similar to the minimum strengths measured in the triaxial tests. The field shear strength was expected to be lower than the triaxial results since the field specimens were failed along foliation surfaces.

Comment

More direct shear tests at different normal loads should have been carried out in the laboratory and field. Normal loads should have varied among specimens in order to obtain a maximum strength failure envelope based on initial failures.

A5 APPENDIX B

GASE HISTORIES INVOLVING TESTS OF FILLED DISCONTINUITIES CASE HISTORY NO. B-l

1. Reference. Evdokimov and Sapegin (1964)*

2. Project. Bratsk HEP Dam, U.S.S.R.

3. Purpose. To study the behavior of a rock block during shear.

4. Location of Test on Project Site. Right abutment area.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The test was conducted on a diabase block having a height of 19 ft and base dimensions of 23 by 23 ft (area 529 sq ft). The block rested on a smooth discontinuity containing a filler of chlorite and serpentine. The block boundary was formed by line drilling using large-diameter bore holes followed by low-level blasting and manual work. The block was inclosed in 2-ft-thick reinforced concrete before testing.

6. Test Conditions, Loading Procedure. Rate of Loading, and Failure Cri­ teria. The normal load was supplied by the block's own weight (21 psi) plus the vertical component of the inclined shear load. The shear load was inclined at 10 47' to the horizontal. The shear stress rate was held to approximately 1.47 psi/min and applied in steps. Each new load was held for over 2 hours until horizontal displacement ceased. Vertical displacements were measured by 27 gages. Horizontal displacements were measured by 37 gages in the sliding direction and 11 gages oriented 90 deg to the sliding direction. The maximum shear stress failure cri­ terion was used. The maximum shear strength was that load which caused continuous sliding.

7. Test Results, Conclusions, and Comments. The normal stress at failure was 36 psi, and the corresponding shear stress was equal to 530 psi. 0 = 56 deg, from the assumption that c = 0 . During shear, initial compression occurred, followed by uplift. Turning of the test block also took place.

References for this appendix are included in the list of literature cited, which follows the main text.

B1 CASE HISTORY NO. B-2

1. Reference. Evdokimov and Sapegin (1970)

2. Project. Kransnoyarsk Dam, U.S.S.R.

3. Purpose. To determine the shear resistance of the dam foundation.

4. Location of Test on Project Site. Tests were conducted in a weak area located near the downstream face of the dam.

5. Preparation and Characteristics of Intact Material or Discontinuity Tested. The material tested was a heavily jointed granite. Two blocks, each 26 by 39 by 23 ft high (base area = 1000 sq ft) were tested. Block 1 was tested in an undisturbed state and block 2 was cement grouted under a pressure of 5 atm approximately 6 months before testing. The upper 20 ft of each block was encased in reinforced concrete, while the lower 3 ft was left exposed. No information on the method of forming the blocks.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal load was produced by piling concrete blocks on a steel truss supported by the test blocks. Flat jacks were used to apply an incremental shear load at an inclination of 15 deg to the horizontal. Vertical and horizontal displacements were measured within the nearest 0.0004 in. The horizontal displacements were measured both parallel and perpendicular to the direction of shear. The specimens were subjected to a series of loading and unloading cycles. Each block was sheared under two normal loads. The maximum shear stress failure criterion was utilized.

7. Test Results, Conci ions, and Comments. Normal Stress Maximum Shear Stress _____ psi______psi______Block 1: 96 134 (ungrouted) 63 96 Block 2: 104 148 (grouted) 64 98 The measured strengths of the grouted and ungrouted rocks are nearly equal. The Mohr-Coulomb shear strength parameters are 0 = 45 deg and c = 37 psi.

During shear, displacement took place along adjacent joints forming a shear zone. Displacement did occur perpendicular to the shear direction in the horizontal plane revealing a rotational movement. Vertical dis­ placement measurements showed (1) the shear loaded face of each block

B2 displaced upward and (2) the middle portion of the blocks moved down­ ward then upward with the grouted block exhibiting the least upward movement.

The modulus of elasticity of each block was also determined. This was done by measuring the vertical compression of each block occurring under the normal load.

B3 CASE HISTORY NO. B-3

1. Reference. James (1969)

2. Project. Muda Dam Site, Northwestern Malaya.

3. Purpose. To determine the effective shear strength parameters of mud­ stone layers interbedded with quartzite. The residual shear strength was especially important.

4. Location of Test on Project Site. The tests were conducted in trenches located in the valley slopes.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Three test blocks of quartzite overlying a mudstone layer were formed by line drilling followed by hand-tool trimming along the desired boundary. The mudstone was described as being weathered and shaley at many points. The blocks were 2 ft high with base dimensions of 2 by 2 ft (area = 4 sq ft). The quartzite block was encased in steel with grout placed between the block and steel casing. The mudstone bed was also inclosed in a steel casing 1 in. or more high. This lower casing could be adjusted to produce failure at any desired level in the mudstone bed. Approximately 1/2 in. spacing was left between the quartzite block casing and mudstone casing.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. Prior to testing, the blocks were kept soaked or otherwise in a wet condition. The normal and horizontal shear loads were provided by hydraulic jacks. The normal loads encompassed those expected to be produced by the dam. An anchored steel beam was used for the normal jack reaction. The shear load jack reacted against a concrete block built along side the excavation.

The three specimens were (1) weathered mudstone seam, (2) slightly weathered mudstone seam, and (3) unweathered mudstone seam. For each specimen the normal load was applied first and the mudstone was allowed to consolidate overnight. The shearing was carried out at a rate of 0.05 in./min, which was considered to be slow enough to allow complete dissipation of pore pressures. An attempt was made to keep the strain rate constant. Initially, the shear load was applied at a maximum rate of 1/4 ton per min. When failure was imminent, the horizontal load was released. The block was then twice resheared under a new normal load. After completion of three tests, the block was restored to its original position and the tests were repeated until residual conditions were reached. Maximum shear stress failure criteria were used with failure being the peak of the shear stress versus horizontal displacement plot.

B4 7. Test Results, Conclusions, and Comments. The failure surface was a noncontinuous series of slickensided undulations within the mudstone, each extending over lengths of about 6 in. The first three tests on each block yielded the following results:

Specimen 0 c No. Deg psi i 20 12 2 18 6 3 26 1.5

The blocks were moved to their original position and resheared several times before residual conditions were obtained. The residual 0 = 1 9 deg while c ranged from 1 to 6 psi for each block.

Laboratory tests on undisturbed and remolded mudstone yielded residual 0 values from 17.5 to 19 deg and c =0. After residual conditions were reached, two blocks were resheared at a rapid displacement rate. No significant difference in the test results was noted suggesting that in the residual condition, the strength is not dependent on the displace­ ment rate. Before residual conditions are reached, a large increase in displacement rate might be expected to produce a change in strength due to excess pore water pressures.

B5 CASE HISTORY NO. B-4

1. Reference. Maddox et al (1967a and 1967b)

2. Project. Meadowbank Dam, Tasmania, Australia

3. Purpose. To measure shear strength along seams which could not be tested in the laboratory.

4. Location of Test on Project Site. No information.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Nine tests were attempted inside four 4-ft-diam calyx drill holes. The test blocks cut from the core were 1.5 ft high and in plan were shaped like three quarters of a circle with a flat face. The diameter of the circle was 3 ft (area about 7 sq ft). The character of the test seams varied: some were zones of brecciated sandstone and mud­ stone a foot or more thick and others contained less than 1/8 in. of fill material between sound rock; some surfaces were relatively smooth, while others were quite irregular. The most satisfactory tests were conducted on a breccia zone in mudstone. The breccia zone was composed of a grey inorganic clayey silt of low plasticity with some rock frag­ ments. Results were also given from a test on a clay-filled joint in sandstone. The clay was slightly organic and of high plasticity.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The seams were allowed to drain freely during testing. The normal load was provided by a hydraulic jack reacting against a steel beam wedged across the calyx hole. Steel rollers were placed between the vertical jack and specimen to reduce friction. The shear load was applied with a hydraulic jack reacting against the side of the calyx hole. The normal stress was applied first. After steady conditions were reached, the shear load was applied in increments allowing move­ ment under each increment to cease or become small. Testing was re­ peated at higher normal loads on the same surface until the piece of core approached the hole wall. Vertical and horizontal displacements were measured during shear.

7. Test Results, Conclusions, and Comments. There were two series of tests. Details of the first series were not given. The second series of tests were performed at a loading rate less than that used for the first series. In the second series, the normal load was held for 3 hr. The shear load increments were held for 15 min after movement had ceased. Failure was assumed to occur when there was a movement of 0.04 to 0.05 in. within 5 min after the application of a load increment. Actual test data are not presented. First series of tests on a silty part of a plane breccia zone in a mudstone bed yielded a 0 = 19 deg and c = 2 psi.

B6 The second test series yielded 0 = 22 deg and c = 1 psi and the hori­ zontal displacement at failure was about 0.1 in.

A slow test on a seam of brown plastic clay in a sandstone bed yielded 0 = 14 deg, c = 1 psi. A consolidated-undrained laboratory triaxial test on remolded clay scraped from the seam after the in situ test yielded a 0 of 19 deg and c of 3 psi. The lower shear resistance measured in the field was said to be the result of failure occurring along naturally occurring weak lamination planes existing in the joint filling.

B7 CASE HISTORY NO. B-5

1. Reference. Pigot and MacKenzie (1961 and 1964).

2. Project. Hydro-Quebec's power development at Carillon on the Ottawa River, Montreal, Canada.

3. Purpose. To measure the shear strength of thin soft altered zones in shale not found during the preliminary drilling.

4. Location of Test on Project Site. The presumed weakest bed in the area was tested. The bed chosen was 10 to 20 ft higher than the foundation surfaces under the sluice section and was located near the south bank of the river, downstream from the sluiceways where there would be mini­ mum interference from construction activity. Tests were carried out in trenches formed by 3-ft-diam calyx drill holes.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The test zone was a 6-in.-thick shale bed containing a 3/8-in.- thick altered zone. The unaltered shale was dense and compact. The altered zone consisted of a soft cohesive material with pieces of un­ altered shale scattered through the matrix. Test blocks were of dolo­ mite which rested on the shale. The shale-dolomite contact was relatively smooth. Test blocks had base dimensions of 2.5 by 2.5 ft (area = 6.25 sq ft) and were formed by drilling 3-ft-diam calyx drill holes to a depth slightly below the shale bed followed by wire-saw cutting between the calyx holes. The blocks were encased in 6-in.-thick reinforced concrete extending down the block sides to within 1 in. of the shale bed.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Criteria. Natural moisture conditions were maintained in the shale by placing a bituminous compound on all exposed shale surfaces. Normal and shear test loads were well above and below those expected to be produced by the dam. Normal load was provided by 100-ton-capacity hydraulic jacks reacting against steel beams spanning the trench. Pressure gages with a range of 0 to 5000 psi were used to measure the normal stress. Roller bearings were located between the vertical jack and test block to minimize friction.

Consolidation from 4 to 20 hr was allowed in 4 of 5 tests before appli­ cation of the shear load. For the fifth test, normal and shear loads were applied simultaneously and the results were not used in determining the Mohr-Coulomb failure envelopes.

Horizontal shear load was applied by hydraulic jacks at a point 5 in. above the test zone. The shear pressure was measured by gages with

B8 ranges of 0 to 1000 psi and 0 to 2000 psi. Displacement rates were kept relatively constant at 0.024 to 0.032 in./min.

Maximum shear stress failure criterion was used; however, in a few of these tests, an initial peak shear stress was reached at a low displace­ ment, after which the shear stress increased. A displacement criterion was then used to determine shear strength. Shear stress at a displace­ ment of 2 in. was used. Average stress rates to initial peaks were: test 1, 13.7 psi/min; test 2, 13.7 psi/min; test 3, 20.0 psi/min; test 4, 8.1 psi/min; and test 5, 6.2 psi/min.

7. Test Results, Conclusions, and Comments. Failure occurred in the altered zone forming a series of shear planes. Corrections in data were made for the effect of reduction in shearing plane area during the tests; however, no explanation was given as to how these corrections were made. The maximum normal stress applied was 100 psi. The maximum shear stress reached was 36 psi at a displacement of 2.4 in. Shear strength para­

meters are: (a) at initial failure or displacement of 0.05 in., 0 * 14 deg, c = 6 psi, (b) at a displacement of 2.0 in., 0 = 18 deg, c = 3 psi.

B9 CASE HISTORY NO. B-6

1. Reference. Uriel (1968)

2. Pro ject. Canelles Dam, Spain

3. Purpose. To determine shear strength along critically located joints.

4. Location of Test on Project Site. Tests were carried out inside adits and tunnels within the dam foundation.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Joints and bedding planes in limestone located at different depths were tested. The tests can be catagorized as follows:

Test Series I: Six blocks were sheared along clay-filled joints. The clay had a liquid limit of 73 percent and plastic limit of 25 percent. Natural moisture content = 56 percent.

Test Series II: Four blocks were sheared along clay- and grout-filled joints. The clay had a liquid limit of 72 percent and plastic limit of 21 percent.

Test Series III: Three blocks were sheared along clay-filled joints. The clay had a liquid limit of 42 percent and plastic limit of 20 per­ cent .

Test Series IV: Four blocks were sheared along clay-filled bedding planes. The clay had a liquid limit of 73 percent and plastic limit of 25 percent.

All of the blocks had base dimensions of 3.3 by 3.3 ft (area = 11 sq ft) . The specimens were isolated and formed by line drilling followed by hand trimming. The loaded surfaces of the test blocks were covered with a layer of concrete.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ terion. The normal and inclined shear loads were applied with hydraulic jacks. The normal load was applied in steps with vertical displacements being allowed to stabilize before applying the shear load. The shear load was applied incrementally until failure. Each specimen was failed only once, and the maximum shear stress failure criterion was utilized. Horizontal and vertical displacements were measured at the test blockfs four corners.

7. Test Results, Conclusions, and Comments.

BIO Closure of Joint Shear Test 0 c Under the Initial Displacement No. deg psi Normal Load, in. at Failure, in. I 28 9.6 0.02-0.54 0.0256-0.62 II 38 11.1 0.004-0.0236 0.0185-0.071 III 35 116.0 0.0055-0.0120 0.037-0.076 IV 49 78.0 0.0004-0.00985 0.027-0.248

Tests III and IV exhibit high shear strengths since the clay filling was of "minimal thickness," allowing greater contact between the joint surfaces. The joints of tests I and II were described as being open "several centimeters." The high strength measured in Test II is likely caused by the grout. Fill material from Tests I and II were tested in the laboratory. Strengths measured were: Fill I, 0 = 15 deg, c = 4 psi Fill II, 0 = 31 deg, c = 13 psi. All the test surfaces contained irreg­ ularities and interlocking along the joint contacts during shear contri­ buted to the measured strength.

Bll CASE HISTORY NO. B-7

1. Reference. Ruiz et al, (1968)

2. Pro ject. Solteiria Dam, Brazil

3. Purpose. To determine the foundation shear strength.

4. Location of Test on Project Site. Majority of tests were conducted in exploratory shafts in the foundation.

5. Preparation and Characteristics of Intact Materials or Discontinuities Tested. Shear resistance along the contact between a compact basalt and basaltic breccia was measured. A compact basalt block was sheared along the contact. The block had base dimensions of approximately 19 by 19 ft (area = 375 sq ft) and a height of 20 ft. A photograph showed the contact to be a zone of fractured rock.

6. Test conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The base of the block was kept saturated during shear. The normal stress was due only to the block weight. The horizontal shear load was applied by hydraulic jacks. Three tests were carried out with the shear direction in the third test being 90 deg to that of tests 1 and 2. Vertical and horizontal displacements were measured with 36 dial micrometer gages. The maximum shear stress failure criterion was utilized.

Test Results, Conclusions, and Comments. If c is assumed to equal test 1 yields 0 = 68 deg.

Normal Stress Shear Stress Total Displacement Test psi psi in. 1 24 64 0.394 2 24 61 0.472 3 24 31 0.79

B12 CASE HISTORY NO. B-8

1. Reference. Salas and Uriel (1964)

2. Project, Mequinenza Dam, Spain. Tests were conducted by the Transpor­ tation and Soil Mechanics Laboratory, Spain.

3- Purpose. To obtain the foundation shear strength.

4. Location of Test on Project Site. The tests were conducted in adits.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Tests were conducted on limestone blocks overlying a thin and slightly irregular lignite layer. The test blocks had base dimensions of 1.64 by 1.64 ft (area = 2.70 sq ft) and 3.28 by 3.28 ft (area = 10.76 sq ft) and were each encased in a steel frame. Mortar was placed between the test block walls and steel frame. A layer of sand was placed between the cover plate and the test block1s upper surface.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri- teria. The normal and inclined shear loads were applied with 50- to 100-metric-ton-capacity hydraulic jacks. No information on loading procedures and rate of loading; however, they were said to be dependent on (1) the type of dam, (2) test location, and (3) predicted load. Either the dilatance criterion or maximum shear stress criterion were utilized. If the inversion from downward to upward displacement did not exist or occurred very close to the maximum shear stress, the maximum shear criterion was used. If the inversion occurred far in advance of total sliding, a detailed study of the test was undertaken to deter­ mine which failure criterion to use. Horizontal and vertical displace­ ments were measured at the four corners of the specimen Vertical displacements measured at the block edge opposite the side to which the shear load was applied were used to locate the inversion point Vert­ ical movement nearest the shear load application point was often upward under very low normal stresses

7. Test Results, Conclusions, and Comments. A straight-line Mohr-Coulomb failure envelope was drawn through the test data. 0 = 34 deg, c = 10 psi. The maximum normal stress attained was 280 psi, and the cor­ responding shear failure stress was 250 psi.

B13 CASE HISTORY NO. B-9

1. Reference. Salas and Uriel (1964)

2. Project. Mequinenza Dam, Spain. Test was conducted by the Transpor­ tation and Soil Mechanics Laboratory, Spain.

3. Purpose. In situ tests had already been conducted (see Case History No. B-8). However, test zone disturbance during specimen preparation may have affected the test results; therefore, another test was carried out. A larger specimen was tested to check if the shear resistance would be higher as was expected.

4. Location of Test on Project Site. The test was conducted in a rectang­ ular adit.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. A limestone block overlying a thin lignite layer was tested. The test specimen was 3.3 ft high with base dimensions of 13 by 13 ft (area = 169 sq ft). The blockfs upper surface and side to which the shear load was applied were encased in 3.3 ft of concrete.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal load was applied by 17 Freyssinet plain jacks arranged in two rows and the inclined shear load was applied by 8 Freyssinet plain jacks. The normal and shear loads were applied in stages. Defor­ mations under the normal stress were allowed to stabilize before apply­ ing the shear stress. No information available on the failure criteria.

7. Test Results, Conclusions, and Comments. At the beginning of shear, the normal stress was 170 psi. At failure, the normal stress was 200 psi and shear strength was 140 psi. These results plotted slightly below the Mohn-Coulomb failure envelope determined from previous small- scale tests where 0 = 34 deg, c = 10 psi (Case History B-8).

B14 CASE HISTORY NO. B-10

1. Reference. Thorfinnson (1954) and Underwood (1964)

2. Project. Fort Randall Dam, Missouri River, in southeastern South Dakota. Tests were carried out by the U. S. Army Corps of Engineers.

3. Purpose. To check results of laboratory tests.

4. Location of Test on Project Site. Test site was located between the outlet works and spillway. Tests were carried out in shallow trenches.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Two chalk blocks resting on a 1/2-in.-thick bentonite seam were tested. The blocks were each 2.5-ft high with base dimensions of 18.8 by 2.5 ft (area = 47 sq ft). A frame building 20 by 40 ft was constructed over the blocks, and heat was provided to protect the blocks during the winter. All exposed surfaces of the chalk blocks and the bentonite seam were coated with a bituminous sealing compound to main­ tain the block!s natural moisture content. No other encasement was used. Grout was placed between the normal load bearing plate and test block.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal load was provided by piling railroad rails on a platform supported by the test blocks. A system of cylindrical rollers was used between the platform and test blocks to minimize friction which was also measured during the test. The horizontal shear load was supplied by a 50-ton-capacity hydraulic jack. The shear load was applied in increments with the load being held constant for 40 min under each increment. Shear stress was applied at rates varying from 0.01 to 0.12 psi/min. Horizontal and vertical strains were measured with Whit­ more strain gages. Displacements as small as 0.0001 in. were measured with dial gages. The test on each block can be separated into six parts. Each part was designed to obtain different information. Cyclic loading and various loading rates were used. No information on failure criteria.

7. Test Results, Conclusions, and Comments. The horizontal compressive stress distribution was determined from the horizontal compressive strain data. The compressive stress difference across a unit segment 1 ft long was determined from the horizontal compressive stress distri­ bution curve. By neglecting the load lost due to roller friction, the entire stress difference was assumed transmitted across the bentonite seam in shear. By Computing the stress difference across a sufficient number of segments, the shear stress distribution was obtained. The compressive strain and shear stress were concentrated near the end of the block to which the shear load was applied.

B15 Blocks 1 and 2 were failed under normal stresses of 42 and 18 psi, respectively. The corresponding maximum shear failure stresses were 294 and 224 psi for blocks 1 and 2, respectively. The maximum shear failure stresses were determined from the shear stress distribution curve.

Horizontal displacement was slightly greater at the front of the test block (where the shear load was applied). The peak shear stress at the front of the test block occurred at a horizontal displacement of about 0.14 in.

Shear strength parameters were determined by assuming a uniform shear stress distribution (i.e., shear stress equal to shear load divided by test area). The shear stress on block 1 and 2 at failure were 29 and 22 psi, respectively. These shear stresses are much lower than the maximum shear stress developed at the front of the block and result in 0 = 16.7 deg, c = 17 psi. Laboratory direct shear tests on samples obtained from 30-in.-diam calyx cores yielded 0 = 18.7 deg, c = 10 psi.

B16 CASE HISTORY NO. B-ll

1. Reference. Underwood (1964)

2. Project. Harlan County Dam, Republican River, south central Nebraska. Tests were carried out by the U. S. Army Corps of Engineers.

3. Purpose. To check results of laboratory direct shear tests conducted on 6-in. core specimens and specimens cut from calyx cores.

4. Location of Test on Project Site. The tests were conducted in the spillway area.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Twelve chalk blocks resting on bentonite seams were tested. The test blocks were 3 ft high with base dimensions of 2.5 by 2.5 ft (area = 6.25 sq ft) and encased in concrete before testing. The ben­ tonite seams had a maximum thickness of 3 in.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. The normal loads, comparable to those imposed by the dam, were applied by a hydraulic jack reacting against two steel beams anchored in bedrock. Complete freedom of movement was obtained by a ball-and- socket bearing and a large roller bearing nest located between the vertical jack and the block. The horizontal shear load was provided by two hydraulic rams placed near the base of the block. Vertical com­ pression, lateral movement, and displacements in direction of shear were measured. Test procedures were as follows. In tests 1-3, the bentonite was consolidated for 14 to 32 hr before shearing at 0.02 in./ min. Blocks 4-6 were unconsolidated and sheared at 0.10 in./min. Blocks 7-9 were subjected to a horizontal load of 60 to 80 percent of the estimated failure stress for a minimum of 12 hr to detect plastic flow or creep in the bentonite. Blocks 10-12 were unconsolidated and sheared at a rate of 0.01 in./min.

7. Test Results, Conclusions, and Comments. Data from each test was not available; however, a straight-line Mohr-Coulomb failure envelope was defined by 0 = 8 deg, c = 2.1 psi. The laboratory direct shear tests on 6-in.-diam cores yielded a greater average shear strength defined by 0 = 14 deg, c = 3.5 psi.

B17 APPENDIX C

GASE HISTORIES INVOLVING TESTS OF INTACT MATERIAL CASE HISTORY NO. C-l

1. Reference. Bukovansky (1966)*

2. Project. Dam site at Nechranice (North Bohemia)

3. Purpose. To aid in determining foundation shear strength.

4. Location of Test on Project Site. No information on location; however, tests were carried out in trenches.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Intact claystone blocks were tested. Test blocks were formed by pressing a steel frame into the soft claystone and excavating around the frame. Two types of frames were used: simple and double. These frames are limited to use in soft rock. Test specimen height varied from 6 to 8 in. Specimens inside the simple frame had rectangular bases (area =2.7 to 10.7 sq ft), and those inside the double frame had a circular base (area = 4.2 sq ft).

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal load was provided by hydraulic jacks reacting against a weighted platform spanning the trench. Normal loads to a maximum of 10 kg/cm^ were applied. Shear load was provided by hydraulic jacks reacting against the trench walls. Natural moisture conditions were maintained when using the double frame. No data on loading procedure, rate of loading, or failure criteria.

7. Test Results, Conclusions, and Comments. Specific test results were not given. Laboratory triaxial tests and field plate load-bearing capacity tests were conducted. Double frame direct shear tests results agreed with laboratory triaxial results. Plate load and simple frame results were lower than laboratory results. Difference was thought to be caused by changes in moisture and stress conditions during prepara­ tion and performance of the simple frame tests.

References for this appendix are included in the list of literature cited, which follows the main text.

Cl CASE HISTORY NO. C-2

1. Reference. Kenty and Meloy (1965)

2. Project. Jones Bluff Lock and Dam, Alabama River. Tests were conducted by the USAE Ohio River Division.

3. Purpose. To develop laboratory and field correlation and to develop criteria for determining in situ shear strength.

4. Location of Test on Project Site. Test site was located about one mile from the proposed lock and dam site.

5. Preparation and Characteristics of Intact Materials and Discontinuity Tested. Material tested was the Selma chalk. The material was classi­ fied as a calcero-argillaceous marl. Composition ranged from highly argillaceous limestone to highly calcareous claystone. Distinct bedding or laminations was lacking. The rock was massive homogeneous and fine grained. Upon drying, the rock developed open cracks. Specimens were 10 in. high with 12- by 12-in. bases and were formed in the same manner as those at Pike Island (see Case History E-8).

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Criteria. Loading apparatus and failure criteria were identical to those used at Pike Island (see Case History E-8). Load increments were added when deformation slowed to 0.001 in. in 3 min. The average shear stress application rate varied from 0.24 to 0.9 psi/min and the average dis­ placement rate was 0.0007 in./min.

7. Test Results. Conclusions, and Comments. Shear surfaces were fairly smooth. Normal stress ranged from 25 to 166 psi with corresponding shear failure stresses of 60 and 125 psi, c = 55 psi, 0 = 22 deg. Largest horizontal displacement at failure was 0.8 in. Times to failure ranged from 129 to 510 min. Laboratory direct shear tests on 6-in.-diam cores resulted in lower shear strength than that measured in the field.

Clab = ^ Ps ^ 5 0 = 22 deg. Laboratory stress rate = 50 psi/min.

C2 CASE HISTORY NO. C-3

1. Reference. Kleiner and Acker (1971)

2. Project. Mossyrock Arch Dam in Washington. Tests carried out by Harza Engineering Company.

3. Purpose. To determine the foundation shear strength.

4. Location of Test on Project Site. Tests were carried out in a chamber adjacent to an exploratory shaft.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The rock tested was described as a gray, massive, amygdaloidal andesite flow. No other information.

6. Test Conditions. Loading Procedure, Rate of Loading, and Failure Cri­ teria. The maximum shear stress criterion and possibly the residual shear stress criterion were utilized. No other information.

7. Test ResultsConclusions, and Comments.

Maximum shear strength: 0 = 54.5 deg, c = 86 psi. Residual shear strength: 0 = 51.5 deg, c = 0

The maximum normal stress was approximately 180 psi, corresponding to a shear stress of 320 psi. Laboratory tests were also carried out on NX-size core specimens of the same type rock. The measured shear strength parameters were identical to those measured in the in situ direct shear test.

Coment - The residual strength parameters given above may not represent the true residual strength. The authors simply assumed that the shear strength available after initial failure was the residual strength.

C3 CASE HISTORY NO. C-4

1. reference. Rocha et al. (1967); Rocha (1964a); Serafim and Lopes (1961); Serafim (1964).

2. Project. Alto Rabagao Dam, Portugal. Tests conducted by LNEC.

3. Purpose. To obtain shear strength of proposed dam foundation and abut­ ment materials.

4. Location of Test on Project Site. Tests were conducted in adits.

5. Preparation and Characteristics of Intact Materials or Discontinuities Tested. The rock tested was a granite displaying variable and sometimes very intense alteration. The 44 blocks tested were each 1 ft high with base dimensions of 2.3 by 2.3 ft (area = 5.3 sq ft). The test blocks were encased in reinforced concrete or a thin layer of mortar and steel frame with sand placed beneath the vertical loading plate. When just reinforced concrete was used, the concrete extended down the block sides, but stopped short of the base.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Criteria. The rock was kept saturated during the tests. Normal and inclined shear load were provided by hydraulic jacks. Horizontal and vertical displace­ ments were measured. The normal load was applied in increments and when the vertical displacements stopped, the shear force was increased in steps with no increment being applied before displacements stopped. Maximum shear stress and dilatance failure criteria were utilized. When using the dilatance criterion, the shear stress, corresponding to that point at which vertical displacements change from downward to up­ ward, was used to plot Mohr-Coulomb failure envelopes. The maximum strength was the maximum shear stress reached during the test.

7. Test Results. Conclusions, and Comments. Strengths determined by the dilatance criterion were generally slightly lower than the maximum shear strength.

Blocks were sheared under normal stresses of 14, 36, 57, and 100 psi. The maximum shear failure stress reported was 650 psi. Cohesion inter­ cept c and friction angle 0 varied and were dependent on rock quality.

A quality index I was defined by I = * where I = the water absorp­ tion in a rock sample, P = weight of the rock sample when saturated, p = weight of rock sample after drying at 105°C. The parameters 0 and c defining the maximum shear strength were compared with the quality index. As I increased from 3 to 31 percent, 0 decreased from 60 to 35 deg, and as I increased from 3 to 10 percent, c decreased from

C4 182 to 28 psi and approached 0 at I = 21 percent. For values of I above 15 percent, the material is no longer a rock, but a residual soil. Laboratory triaxial tests were also carried out on the weathered granite. Field and laboratory tests results were similar.

Comment - The parameter I may only reflect the intact rock shear strength and not the strength along a discontinuity.

C5 CASE HISTORY NO. C-5

1. Reference. Ruiz and Camargo (1966)

2. Project. Jupia Dam on the Parana River, Brazil. Tests were conducted by the LNEC, Portugal.

3. Purpose. To determine shear strength of foundation and abutment rock.

4. Location of Test on Project Site. Tests were conducted in tunnels and test adits.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Nine tests were carried out in sandstone, vesicular basalt, and sandstone basalt breccia. The blocks were 12 in. high with base dimen­ sions of 28 by 28 in. (area = 5.3 sq ft).

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. The normal and shear loads were provided by hydraulic jacks. Three failure criteria were utilized:

(a) Dilatance criterion represented by the shear and normal stresses corresponding to the inversion of vertical displacements from downward to upward.

(b) Displacement criterion represented by shear and normal stresses corresponding to a horizontal displacement of 0.04 in.

(c) Maximum shear stress criterion represented by the maximum shear stress reached during the test.

7. Test Results. Conclusions, and Comments. Although, different types of rocks were tested, the test results were combined when plotting Mohr- Coulomb failure envelopes:

(a) Dilatance criterion: 0 = 61 deg, c = 50 psi

(b) Displacement criterion: 0 = 57 deg, c = 100 psi

(c) Maximum shear stress criterion: 0 = 59 deg, c = 140 psi

The maximum normal stress applied was 280 psi with corresponding shear failure at approximately 570 psi.

C6 CASE HISTORY NO. C-6

1. Reference. Serafim and Folque (1957)

2. Project. Pisoes Dam. The tests were conducted by LNEC, Portugal.

3. Purpose. To determine the foundation shear strength.

4. Location of Test on Project Site. The tests were carried out in four trenches. Four or five tests were conducted in each trench.

5. Preparation and Characteristics of Intact Material or Discontinuities Tested. Tests were carried out on intact blocks of altered granite. The granite blocks were encased in a steel frame. A thin layer of mortar was placed between the block sides and steel frame. A layer of sand was placed on the block1s upper surface beneath the cover plate. The blocks were 1.15 ft high with base dimensions of 2.3 by 2.3 ft (area =5.3 sq ft).

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Criteria. The normal and inclined shear load were applied with hydraulic jacks. Vertical and horizontal displacements were also measured. No other information.

7. Test Results, Conclusions, and Comments. The results of five tests conducted in one trench were:

Normal Shear Stress Failure Displacement in Shear Test psi Stress, psi Direction at Failure, in,

i 0 71 0.16 2 14.2 128 0.36 3 28 185 0.4 4 28 196 0.44 5 100 213 0.75

The Mohr failure envelope was approximated by two straight lines. At normal stresses less than 71 psi, 0 = 60 deg and c = 40 psi; at normal stress greater than 71 psi, 0 = 22 deg and c = 142 psi.

C7 APPENDIX D

CASE HISTORIES INVOLVING TESTS OF CONCRETE BLOCKS CAST ON ROCK SURFACES CASE HISTORY NO. D-l

1. Reference. Dvorak (1957)^

2. Project. No information.

3. Purpose. To investigate shear resistance of dam foundation rocks.

4. Location of Test on Project Site, No information.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Reinforced concrete blocks cast on sandstone interbedded with shale. Block height = 1.6 ft. Base dimensions = 2.3 by 2.3 ft (area = 5.3 sq ft).

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. Inclined shear load and vertical load are applied by hydraulic jacks. A roller bearing was placed between block and jack to keep load vertical and reduce friction during shear. No other information.

7. Tests Results, Conclusions, and Comments. Shear occurred within the rock. The blocks were failed at normal stresses of 67, 82, 110, and 124 psi. The corresponding shear failure stresses were 52, 60, 78, and 82 psi. The normal stresses included the vertical component of the inclined shear load. The resulting Mohr-Coulomb shear parameters were 0 = 30 deg and c = 13.5 psi.

References for this appendix are included in the list of literature cited, which follows the main text.

D1 CASE HISTORY NO. D-2

1. Reference. Evdokimov and Sapegin (1964)

2. Project. Bratsk HEP Dam, U.S.S.R.

3. Purpose. To obtain sliding resistance of concrete on rock.

4. Location of Test on Project Site. Tests were run in adits and trenches.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks were cast on a heavily fractured diabase and a compact diabase. The rock surfaces were prepared by manual work to different degrees of roughness with protrusions and recesses from 0 to 6 in. deep. Twenty-eight of the blocks tested had base dimensions of 3.3 by 3.3 ft and areas of 10.8 sq ft. Eight other blocks had base dimensions of 6.6 by 6.6 ft and areas of 44 sq ft.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria . Tests were performed with the concrete-rock contact submerged. Normal and shear loads were applied by hydraulic jacks. Normal load jack reaction was provided by an anchored steel girder spanning the trench. Rollers were placed between the support beam and jack to reduce friction. The normal load was kept constant while a horizontal shear load was applied in steps. Maximum normal load used was approximately 280 psi and shear load was 710 psi. The maximum shear stress failure criterion was used with the failure load being that which caused con­ tinuous horizontal displacement. Horizontal and vertical displacements' were measured with gages having an accuracy of 0.0004 to 0.0001 in. Wooden beams were placed between reaction structure and loading pad to act as elastic padding to allow free vertical movement. Specimens were retested under new normal loads after initial failure.

7. Test Results, Conclusions, and Comments. The blocks exhibited a high initial strength with a decrease in shear strength with continued dis­ placement. Tilting and shifting of the test blocks occurred. Residual strength was claimed to have been reached within a horizontal displace­ ment of 0.06 in. The failure surface location varied. The shear strength parameters were as follows:

Heavily fractured diabase, shear through rock:

a. Initial failure, 0 = 32 deg, c = 19.6 psi.

b. Repetitive testing, 0 = 33 deg, c = 18.3 psi

D2 Compact diabase, location of shear surface varied: a. Initial failure, 0 = 38 deg, c = 170 psi b. Repetitive testing, 0 = 45 deg, c = 66 psi

Shear strength was also compared with surface roughness. Values of 0 and c increased with increasing roughness.

D3 CASE HISTORY NO. D-3

1. Reference. Hirschfeld et al. (1965)

2. Project. Third locks studies at Panama Canal, carried out in 1939.

3. Purpose. To obtain shear strength to be used in slope stability analysis.

4. Location of Test on Project Site. Tests were conducted in adits 6 ft high by 5 ft wide and excavated 45 ft back into the Cucaracha clay shale.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks were cast on grooved clay-shale surfaces. The blocks had 1-ft-square bases.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. The normal and shear loads were applied by hydraulic jacks re­ acting against the test adit roof and walls, respectively. Two tests were conducted at a normal stress of 55 psi and four tests at 105 psi. The shear load was applied in increments. The maximum and residual shear strengths were determined. Maximum shear stress criterion - shear load necessary to maintain continuous movement of the block. Residual shear stress criterion - the block was allowed to move some distance after initial failure; the shear load was then removed and reapplied in increments until continuous movement began with the shear load remaining constant.

7. Test Results. Conclusions, and Comments. The shear plane always occurred within the shale. The depth of the shear plane appeared to be governed by the position of slickensides. Mohr-Coulomb failure envelopes were drawn.

Maximum strength criterion - 0 = 21.6 deg, c = 9 psi Residual strength criterion - 0 = 8.8 deg, c = 16.7 psi

The maximum shear stress attained was 70 psi under a normal load of 105 psi.

Comment - The maximum strength may be the intact strength of the clay shale (i.e., the shear stress needed to cause initial fracture). The residual strength is therefore a strength remaining after some displace­ ment, but may not actually be the true residual strength of the clay shale.

D4 CASE HISTORY NO. D-4

1. Reference. Kenty and Meloy (1965)

2. Project. Belleville Locks and Dam, Ohio River; Cannelton Locks and Dam, Ohio River; and Jones Bluff Lock and Dam, Alabama River. Tests were carried out by the USAE Ohio River Division.

3. Purpose. To determine the strength along the concrete-rock contact.

4. Location of Test on Project Site. Same location indicated in Case Histories E-9, E-10, and C-2.

5. Preparation and Characteristics of Intact Materials of Discontinuity Tested. The upper half of each sheared specimen was discarded and a cement-sand grout was placed on the sheared surface. The sheared sur­ face was left as sheared except that any loose pieces of rock were removed prior to the placing of grout. One to 1-1/2 in. of grout was placed, followed by concrete filling the steel shear box. An exception was at Jones* Bluff where only grout filled the steel shear box. The procedure was designed to simulate field conditions where a layer of grout is placed on the bedrock before the concrete. Specific propor­ tions are:

Belleville claystone - Cemenf.Fly Ash: Sand = 1:0.275:3 Water/Cement ratio = 0.48

Cannelton Degonia shale - Cement:Sand = 1:3

Jones Bluff Selma chalk - Cement:Sand = 1:3

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. After curing for 7 days under moist burlap, the specimens were sheared with the same procedures as for direct shear of rock, see Case Histories E-9, E-10, and C-2.

7. Test Results, Conclusions, and Comments.

Belleville Locks and Dam. Sheared surfaces were slightly undulating. Shear planes included areas of shear of bond, shear of rock, and shear of grout. Normal stress ranged from 50 to 125 psi with corresponding shear failure stresses of 65 and 125 psi. 0 = 34 deg, c = 25 psi. Times to failure ranged from 97 to 204 min. Largest horizontal dis­ placement at failure was 0.1 in. Strength of grout-claystone contact was slightly higher than that of claystone up to a normal stress of 125 psi.

D5 Cannelton Locks and Dam. Sheared surfaces were fairly smooth. The shear plane included areas of shear of bond, shear of rock, and shear grout. Normal stresses ranged from 50 to 125 psi with corresponding shear failure stresses of 50 and 85 psi. 0 = 39 deg, c = 0. Times to failure ranged from 82 to 184 min. Largest horizontal displacement at failure was 0.07 in. Laboratory tests of 6-in.-diam core specimens resulted in slightly higher strength. Strength of grout-shale contact was less than that of shale up to a normal stress of 90 psi.

Jones Bluff Lock and Dam. Sheared surfaces were smooth and located primarily along the contact between the grout and marl. Normal stress ranged from 25 to 165 psi with corresponding shear failure stresses of 60 and 140 psi. 0 = 30 deg, c = 30 psi. Times to failure ranged from 66 to 340 min. Largest horizontal displacenE nt at failure was 0.2 in. Tests in laboratory on 6-in.-diam core specimens resulted in approxi­ mately the same strength. Strength of grout-marl contact was slightly less than that of intact marl up to a normal stress of 145 psi. Kenty and Meloy concluded that intensity of normal stress determines whether strength of rock or strength of bond will govern stability.

D6 CASE HISTORY NO. D-5

1. Reference. Krsmanovic and Popovic (1966)

2. Project. Grancarevo Dam, Yugoslavia

3. Purpose. To measure the shear strength along concrete-limestone contacts.

4. Location of Test on Project Site. Tests carried out in adits and tunnels.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks were cast on previously sheared limestone surfaces. The surfaces were cleaned before placement of concrete, except for one surface which had left on it, a thin layer of clayey material.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. Loading apparatus, procedure, rate of loading, and failure criteria are assumed to be the same as those described in Case History E-ll.

7. Test Results, Conclusions, and Comments. Mohr failure envelopes were nonlinear. Maximum normal stress was 350 psi. Maximum shear failure stress was about 420 psi. Cohesion c was zero, indicating that the bond strength was very small. By approximating the test results with two straight lines, the following shear parameters are obtained:

At normal stresses < 71 psi: 0 ^ 65 deg, c = 0 At normal stresses > 71 psi: 0 ^ 35 deg, c = 11 psi

D7 CASE HISTORY NO. D-6

1. Reference. Multipurpose Dam Rock Testing Group, Japan (1964)

2. Project. Shijushida Dam, Japan

3. Purpose, Tests were conducted to determine if the bedrock was suitable as a dam foundation.

4. Location of Test on Project Site. Tests were conducted in adits.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks were cast on levelled rock surface of jointed diabase and tuff. The blocks were 1.15 ft high with square bases (1.96 by 1.96 ft ; area = 3.84 sq ft).

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal and shear loads were provided by 100-metric-ton- capacity hydraulic jacks. The shear load was inclined to the horizon­ tal. Vertical and horizontal displacement were measured by four dial gages.

7. Test Results, Conclusions, and Comments. The maximum normal stress applied was 430 psi with a corresponding shear failure stress of 710 psi. The parameters 0 and c could not be determined from the scattered data (comment) .

D8 CASE HISTORY NO. D-7

1. Reference. Niederhoff (1939)

2. Project, Possum Kingdom Dam, Texas

3. Purpose. To obtain data for estimating probable movement of a masonry dam along its foundation.

4. Location of Test on Project Site. Tests were conducted in trenches.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks were cast on irregular surfaces of a fine­ grained shale. The irregular surfaces were formed by air tool and hand excavation. The surfaces were believed to represent the surface upon which the dam would rest. The shale was found to slake in water after being dried. Eight blocks were tested but only three were reported upon. Test block dimensions were 5 by 5 by 5 ft.

5. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria . To preserve the shalefs natural moisture conditions, asphalt solution was sprayed on the exposed surfaces. The concrete blocks were cast directly on the asphalt coating. The test apparatus con­ sisted of vertical and horizontal hydraulic jacks. The vertical jack reacted against a weighted platform spanning the trench and the hori­ zontal jack reacted against the trench wall. Horizontal and vertical displacements were measured with dial gages capable of measuring move­ ment as low as 0.001 in. The maximum shear failure criterion was utilized. Immediately after the normal load was established, the hori­ zontal load was applied and increased until initial failure. After failure, the loads were released and reapplied to obtain the concrete on shale sliding friction. Average loading rates are:

Test 1 - 0.76 psi/min at average displacement rate of 0.003 in./min. Test 2 - 1.03 psi/min at average displacement rate of 0.006 in./min. Test 3 - 0.78 psi/min at average displacement rate of 0.005 in./min.

7. Test Results, Conclusions, and Comments.

Test 1. Normal stress = 13.1 psi; shear stress at failure 18.2 psi at a displacement of 0.08 in. in shear direction; time to failure = 24 min failure was mostly along concrete-shale contact.

Test 2. Normal stress = 37 psi; shear stress at failure = 35 psi at a displacement of 0.2 in. in shear direction; time to failure = 34 min; failure was mostly along concrete-shale contact. From tests 1 and 2, 0 = 36 deg, c = 8 psi.

D9 Test 3. Normal stress = 44 psi; shear stress at failure = 37 psi; at a displacement of 0.2 in. in shear direction; time to failure = 47 min. Failure was within a portion of shale reported to be much weaker than the shale under the blocks of test 1 and 2. From test 3, 0 = 38 deg by assuming c = 0.

DIO CASE HISTORY NO. D-8

1. Reference. Rountree (1940)

2. Project. Watts Bar Dam, Tennessee River

3. Purpose. To obtain the foundation shear strength.

4. Location of Test on Project Site. Tests were carried out in trenches.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The material tested was a cemented, clayey and silty shale. The shale was fairly compact and unweathered; however, it was charac­ terized as fissile and was comprised of very thin layers which were easily separated. The shale was interbedded with 1/8- to 2-in.-thick layers of hard sandstone spaced at 1 to 24 in. Six concrete blocks were cast directly on the shale bedding planes. Test blocks were 4.5 ft high with 5 by 3 ft bases (base area = 15 sq ft).

6. Test Conditions, Loading Procedures, Rate of Loading» and Failure Cri­ teria. Immediately before testing, the shale along each block*s base was trenched to an approximate depth of 2 in. below the contact surface. This procedure removed any lateral support of the shale, which simulates true conditions under an actual concrete gravity dam. The normal and shear loads were applied by hydraulic jacks. Average loading rates are: Test 1, 5 psi/min; Test 2, 4 psi/min; Test 3, 0.8 psi/min; Test 4, 0.9 psi/min; Tests 5 and 6, 3.3 psi/min. Consolidation of 64, 70, 55, and 74 min was allowed under a sustained vertical load for blocks 1 through 4, respectively. Shear load was applied in increments to blocks 5 and 6 immediately after the vertical load was attained. Maxi­ mum shear stress failure criterion was used. The failure shear stress caused continuous movement. Horizontal and vertical displacements as small as 0.001 in. were measured. Average rate of displacement for test block 4 was 0.0013 in./min. After initial failure loads were released and reapplied to obtain the sliding resistance.

7. Test Results, Conclusions, and Comments. Failure occurred within shale about 1/2 to 2 in. below the contact.

Test Normal Shear Stress Block Stress, psi at Failure, psi Time to Failure, min. 1 80 42 9 2 61 70 19 3 29 26 31 4 71 42 48 5 28 25 7 6 68 31 9

Dll Maximum shear strength parameters are 0 = 23 deg, c = 13 psi. Sliding friction, 0 = 28 deg, c = 0.

The author stated that irregularities were still being sheared off during sliding; therefore, the sliding friction is not a residual shear strength (comment) . CASE HISTORY NO. D-9

1. Reference. Sarmento and Vaz (1964)

2. Pro ject. Cambambe Dam, Angola

3. Purpose. To determine the foundation shear strength.

4. Location of Test on Project Site. No information.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks were cast on surfaces of three different type rocks: (a) medium-grained sandstone, (b) fine-grained sandstone, (c) clay shale.

6. Test Conditions„ Loading Procedure, Rate of Loading, and Failure Cri­ teria . Each block was tested at a different normal load. The vertical and inclined shear loads were applied simultaneously with the vertical stress being held constant during testing. No other information pre­ sented.

7. Test Results, Conclusions, and Comments.

Medium-grained sandstone: 0 = 51 deg, c = 14 psi Fine-grained sandstone: 0 = 48 deg, c = 7 psi Clay shale: 0 = 45 deg, c = 28 psi

D13 CASE HISTORY NO. D-10

1. Reference. Scott, Reeve, and Germond (1968)

2. Project. Farahnaz Pahlavi Dam, Iran

3. Purpose. To obtain the shear resistance along a concrete on rock contact.

4. Location of Test on Project Site. Tests were carried out in trenches in the left abutment area.

3. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Two concrete blocks were cast directly on the rock surface. No information on the type of rock. The test blocks were about 3 ft high with base dimensions of 5.25 by 3.28 ft (area = 17.5 sq ft).

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal loads were produced by posttensioned cables anchored at some depth beneath the concrete blocks. Flat jacks were used to apply the shear load at opposite ends of the block. So-called "active” horizontal forces were applied to one face and resisted by a "passive" force on the opposite face combined with the shear resistance along the concrete-rock contact. Loading and unloading cycles of active force were applied under normal stresses of 159, 119, 79, and 40 psi, and repeated and failed at 25.2 psi with the passive jack removed.

7. Test Results, Conclusions, and Comments. The author states that shear failure occurred when the shear stresses were at least three times those that were predicted to act on the foundation. Displacement measure­ ments showed that 40 percent of the horizontal displacements which occurred under the first loading cycle were permanent. This permanent displacement was thought to be due to closing of fissures. Data were insufficient for determination of 0 and c .

D14 CASE HISTORY NO. D-ll

1. Reference. Serafim and Guerriero (1968)

2. Pro iect. Janovas Dam, Spain

3. Purpose. To determine the shear resistance along concrete-rock contacts.

4. Location of Test on Project Site. Dam foundation area.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Results were reported on the following tests:

1. Concrete blocks cast on clean limestone surfaces. 2. Concrete blocks cast on limestone surfaces containing a thin film of clay.

Base dimensions of specimens: 2.3 by 2.3 ft (area = 5.3 sq ft). Con­ crete blocks were cured for 8 days before testing.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. Single jack loading was utilized as described in Case History E-14. Maximum shear stress failure criterion was employed. Concrete blocks were failed, each under a different normal load, in order to obtain Mohr-Coulomb failure envelopes.

7. Test Results. Conclusions, and Comments. In tests of concrete on the clean limestone surfaces, failure usually took place either along the concrete-rock contact or partially along the contact and through the concrete. For only one block did failure take place immediately beneath the contact partially through intact rock and along a joint. Where the clay was present, failure occurred only along concrete-rock contact.

Strength parameters were:

Concrete-clean limestone contact, 0 ^ 61 deg, c ~ 80 psi Concrete-limestone with clay film contact, 0 ^ 44 deg, c & 25 psi APPENDIX E

CASE HISTORIES INVOLVING TESTS OF VARIOUS CONDITIONS CASE HISTORY NO. E-l

1. Reference. Boughton and Hale (1967)*

2. Project. Cethana Dam Site, Tasmania, Australia

3. Purpose. To obtain approximate shear strength of various discontinuities.

4. Location of Test on Project Site. Exploratory adits in left abutment.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested.

Test 1 on a 1-in.-thick bedding-plane shear zone in quartzite. Test 2 on a 0 .4-in.-thick bedding-plane shear zone in quartzite. Test 3 on a smooth joint.

Shear zones consisted of rock flour and fragments, chlorite, and minor amounts of clay minerals. Shear surface for each block was 20 by 20 in. (area = 2.78 sq ft).

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. Surfaces were tested wet under normal loads of 100 to 400 psi. No data on loading procedure, rate of loading, or failure criteria; however, repetitive testing was likely utilized along with the maximum shear stress failure criterion.

7. Test Results. Conclusions, and Comments.

Test 1, 0 = 23 deg, c = 7.5 psi Test 2, 0 = 36 deg, c = 75 psi Test 3, 0 = 24 deg, c = 25 psi

Remolded material from the bedding-plane shears was tested in triaxial tests carried out in the laboratory. The results were 0 = 31 deg, c < 10 psi. Nineteen laboratory direct shear tests were also carried out on joints in 4-in.-diam drill cores and on rock specimens from sur­ face or underground excavations. Field tests 2 and 3 were averaged with the laboratory direct shear results to obtain design 0 values. Cohesion was neglected.

References for this appendix are included in the list of literature cited, which follows the main text.

El CASE HISTORY NO. E-2

1. Reference. Drozd (1967)

2. Project, Dam sites in Czechoslovakia

3. Purpose. To study techniques and interpretation of in situ direct shear tests.

4. Location of Test on Project Site. Tests were conducted in tunnels and test adits.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested.

Test 1: bedding plane in greywacke filled with 1 to 2 mm of clay. Test la: clean bedding plane in greywacke. Test 2: schistosity plane in amphibolite. Test 3: slightly weathered amphibolite with shearing planes transverse to schistosity planes. Test 4: fissured plane in gneiss. Test 5: two chlorite schist blocks with displacement in direction of schistosity. Test 6: intact mica-schist-gneiss with displacement across direction of schistosity. Test 7: contact plane of concrete on greywacke.

Test area ranged from 3.2 to 8.6 sq ft. A layer of concrete was used as the vertical loading plate, and on some blocks a layer of plaster was used as the shear-load bearing plate. A steel frame was placed around weak rocks and space between rock and frame was filled with con­ crete .

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. Shear surface was constantly watered or submerged during tests. Normal and shear loads were applied by hydraulic jacks of "50-100- metric ^ ton n capacity and measured with dynamometers accurate within 2 percent. To reduce friction, rollers were placed between normal load jack and test specimens. Shear load was slightly inclined since earlier tests with horizontal loading caused tilting. Each test was carried out in two stages:

Stage A - Normal load was applied and the inclined shear load gradually increased until failure. The failure criterion used under stage A was

E2 the maximum shear stress criterion. The failure load caused steady move­ ment of the block and represented the maximum shear strength.

Stage B - The normal load was doubled then decreased in steps and the specimen resheared at each new normal load. Stage B was also repeated three times on each block to determine the change in strength with dis­ placement. Maximum shear stress failure criterion was again utilized.

7. Test Results, Conclusions, and Comments. Plots of failure shear stress and normal stress are given for failure under stage A and B, and repe­ titions of stage B. Repetitive testing in stage B revealed that for some specimens, the shear strength decreased with increasing displace­ ment. Drozd assumed that stage B always measured residual shear strength and therefore concluded that the residual shear strength decreased with displacement. (Comment - A better interpretation might be that shear strength decreases with displacement until the residual shear strength is reached.)

Of special interest were the results of test No. 1 carried out on a bedding plane in greywacke filled with 1 to 2 mm of clay. A greater shear strength was measured in stage B than in stage A. There are two possible reasons for this: (1) the effective normal stress was probably higher in stage B than in stage A and (2) the fill material was squeezed out during testing which allowed the surfaces of the discontinuity to come in closer contact. Drozd suggests that pore water pressures be measured within the fill material during testing.

Shear strength parameters determined by straight line approximations of stage B results were found to be as follows:

0 c Test de8 psi Remarks 1 23 0 Stage A results were slightly less la 30 14 Agrees with stage A results 2 46 0 Much greater strength measured in stage B 3 63 18 Agrees with strength measured in stage A. Strength was found to decrease with repe­ titions of stage B. 4 45 25 Much greater strength measured in stage A. 5 10 7 Agrees with strength measured in stage A. Strength decreased in repetitions of stage B. 6 57 70 Agrees with strength measured in stage A 7 39 42 Strength in stage A was greater

E3 Where the strength measured upon initial failure in stage A was much greater than that of stage B, c is assumed to equal 0 and the following values of 0 were determined:

Test 2, 0 = 70 deg Test 4, 0 = 65 deg Test 7, 0 = 52 deg

E4 CASE HISTORY NO. E-3

1. Reference. Dvorak and Peter (1961)

2. Project. No information.

3. Purpose. No information.

4. Location of Test on Project Site. No information.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Concrete blocks cast on rock surfaces of granulite, gneiss, and dolomite. Soft rock blocks encased in steel frames were also tested. Specimens* base dimensions ranged from 1.6 to 3.3 ft square corres­ ponding to areas of 2.5 to 10 sq ft.

6. Test Conditions, Loading; Procedure, Rate of Loading» and Failure Cri­ teria. Three normal loads were used with two tests at each load. Both inclined and horizontal shear loads were utilized.

7. Test Results, Conclusions, and Comments. Granulite tested with shear force parallel to bedding: 0 = 38 deg, c = 142 psi.

Gneiss tested with shear force perpendicular to foliation: 0 = 35 deg, c = 14 psi.

Dolomite: Data scattered.

E5 CASE HISTORY NO. E-4

1. Reference. Gole and Mokhashi (1970)

2. Project. Tawa Dam, India

3. Purpose. In situ tests were to supplement laboratory tests.

4. Location of Test on Project Site. No information.

5. Preparation and Characteristics of Intact Material or Discontinuity Tested. Tests were conducted on sandstones, shales, shale-sandstone contacts, and concrete blocks cast on sandstone. The rock specimens had dimensions of 3 by 1 by 1 ft high (base area = 3 sq ft). A capping of cement mortar was used to make a level upper surface. To reduce friction, rollers were placed between the normal load jack and test block's upper surface.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal and horizontal shear load were provided by hydraulic jacks. Horizontal displacements were measured to the nearest 0.0001 in. Loading procedure, rate of loading, and failure criteria were not dis­ cussed.

7. Test Results, Conclusions, and Comments.

Concrete on sandstone: 0 = 44 deg, c = 71 psi Sandstone-shale contact: 0 = 32 deg, c = 10 psi Bedding planes in sandstone: 0 = 42 deg, c = 8 psi Discontinuous bedding planes in sandstone: 0=53 deg, c = 42 psi Intact sandstone: 0 = 60 deg, c = 140 psi

E6 CASE HISTORY NO. E-5

1. Reference. Haverland and Butler (1970)

2. Project. Grand Coulee third powerplant, Washington. Tests carried out in the area of the Forebay Dam by the U. S. Bureau of Reclamation, Denver, Colorado.

3. Purpose. To determine shear strength parameters for use in design.

4. Location of Test on Project Site. Tests were conducted on joints con­ tained in an outcrop of granite near the powerplant. These joints were considered typical of joints located throughout the Forebay area.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested, One-quarter of the rock outcrop was removed to a depth of 20 ft. Six test sites were then selected. A large block of rock was first excavated to expose the proposed test block*s upper surface which was cut parallel to the proposed test surface. An NX-size hole was drilled 22 ft deep perpendicular to and at the center of the exposed test surface. A 25-ft-long cable was then grouted into the hole. A bearing plate, ram, and cable clamps were then placed on a thin concrete pad atop the specimen. The cable was tensioned an amount to produce a 5-psi pressure on the test surface. The purpose of the 5-psi normal stress was to hold the joint intact, preventing excessive disturbance during the final isolation of the test block. Power sawing was used to isolate the 15 by 15 by 8 in. high block (test area = 1.6 sq ft). Specimens were encased in a steel frame before testing.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. Normal and a 10-deg inclined shear loads were applied with 60-ton hydraulic rams; repetitive testing was utilized. The initial test was conducted at a normal stress (100 psi) equivalent to that which would exist after construction. Two types of shear loading were utilized: (1) continuously increasing until sliding and (2) incremental loading. Vertical movement and horizontal displacement parallel and perpendicular to the direction of shear were measured. Displacements were measured with linear variable displacement transducers (LVDT*s). The LVDT*s were connected through exciter-demodulator units to recorders. The maximum shear stress failure criterion was utilized; however, after the initial test, the maximum shear stress under each following normal stress was assumed to be a residual or sliding shear resistance.

7. Test Results, Conclusions, and Comments. Mohr-Coulomb shear strength parameters for four field specimens were reported to be as follows:

E7 Description of Joints Sliding Shear Strength Remark

Block 4a: Tight, partially 0 = 40 deg 44 psi Initial strength discontinuous slightly higher Block 2b: Open, clay filled 0 = 24 deg 18 psi Initial strength was similar Block lc: Open, clay filled 0 = 39 deg 18 psi Initial strength was similar Block 5d: Very tight, dis­ 0 = 36 deg 19 psi Initial strength continuous was much higher

Haverland and Butler (1970) suggest that the shear strength not be extrapolated beyond the test data. The highest normal stress at failure was 478 psi. The highest shear failure stress was 386 psi.

E8 CASE HISTORY NO. E-6

1. Reference. John (1961); Nose (1964)

2. Project. Kurobe IV Dam located in the Japanese Alps

3. Purpose. The test program was devised by the Engineering Bureau for Geology and Civil Engineering and the International Experiment Station for Construction in Rock, both located in Salzburg. In situ tests were carried out in conjunction with laboratory tests in order to obtain a correlation which would allow strength estimates to be made where in situ tests had not been carried out.

4. Location of Test on Project. The tests were conducted in the abutment areas within tunnels and adits.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Tests were conducted in a jointed and faulted biotite granite. The tests were divided into three categories or groups: (a) concrete blocks cast on the rock surface (three tests); (b) rock blocks repre­ sentative of the rock mass (two tests); and (c) rock blocks resting on faults or joints (two tests). Dimensions of blocks were as follows:

_____ Base Height Perimeter Area Group ft ft sq ft

a 6.24 12.3 by 8.2 100 b 6 11.5 by 8.2 94 c 5 4.6 by 6.9 31.7

Excavation operations within 3 ft of the test zone were restricted to manual work.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. Test zones were saturated immediately before testing to simulate conditions expected after the dam was finished. Normal loads were applied by flat jacks and shear loads were applied by piston jacks. Shear load was increased in equal increments and new increments were not applied until movement under the preceding load had ceased. Two types of loading were utilized: (a) static loading with three alternate load cycles at each increment; and (b) alternate loading with 200 alternate load cycles at a certain stage of loading. The exact nature of "static11 and "alter­ nate" loading as defined by Nose (1964) is unclear. Vertical and hori­ zontal displacements were measured with induction and resistance-type electrical gages having an accuracy of + 0.0002 in. Maximum shear stress failure criterion was used.

E9 7. Test Results, Conclusions, and Comments.

a. Concrete blocks. Failure took place within the rock just beneath the concrete.

Normal Stress Shear Failure Stress psi psi 185 385 230 510 71 300 170 330 155 300 300 540

From the data, 0 = 45 deg, c = 180 psi.

b. Rock blocks representative of the rock mass. Cracks were initiated on the shear-loaded side of the block and extended gradually to the opposite side.

Normal Stress Shear Failure Stress psi ____ Psi______28 300 71 540

From the data 0 = 78 deg, c = 160 psi.

c. Rock blocks resting on a fault filled with 5 mm of loose sandy material.

Normal Stress Shear Failure Stress psi psi 58 58 155 170

From the data, 0 = 47 deg, c = 0.

Among the data presented, the maximum horizontal displacement was 1 in. To supplement the in situ direct shear tests, compression and triaxial tests were conducted in the laboratory on core specimens and triaxial tests were carried out on rock blocks in the field. Laboratory core specimens exhibited higher shear strength than those measured in field direct shear tests.

E10 CASE HISTORY NO. E-7

1. Reference, Kimishima et al. (1970)

2. Project. None specified

3. Purpose, To study strain behavior of a rock block during direct shear.

4. Location of Test on Project Site. Tests were conducted in adits.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Four blocks of liparite were tested. Each block was considered to represent the rock mass and contained at least 10 very tight joints oriented in various directions. The heights and base dimensions of the blocks were as follows:

Base Height Perimeter Area Block ft ft_____ sq ft I 2.5 5.6 by 4.9 27.5 II 2.5 5.6 by 4.9 27.5 III 3.28 5.25 by 4.25 22.3 IV 2.3 5.9 by 3.9 23

The blocks were encased in concrete before testing.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. The normal and shear loads were applied by hydraulic jacks. The shear load inclination varied: Block I - 20 deg, Block II - 30 deg, Block III - horizontal, Block IV - 10 deg. The shear load was applied at an average rate of approximately 5.7 psi/min. The initial normal stress was 82 psi. Loads were measured with load cells connected to the hydraulic jacks. Displacements were measured laterally and in direction of shear with Carlson-type joint meters. Polyestel strain gages were attached to the sides of block III. Photoelastic coatings were also placed on the side surface to observe differential strain. Maximum shear stress failure criterion was used.

7. Test Results, Conclusions, and Comments. Each block failed at a normal stress of approximately 29 psi and shear stress of 71 psi. At 70 per­ cent of the ultimate load, displacement in the shear direction reached approximately 0.4 in. Lateral expansion at failure was about 0.16 in. Strain measurements indicated that most of the straining in the direction of shear occurred near the shear loading surface. A stress distribution determined from the strain observations is given in the reference.

Ell Sparking and rock noise were apparent during shear. The failure sur­ face was highly irregular and diagonal cracks extended from the shear surface. By assuming that c = 0, a value of 0 was determined as 68 deg.

Failure appeared to have taken place through intact material and along preexisting joints (comment).

E12 CASE HISTORY NO. E-8

1. Reference, Kenty and Meloy (1965)

2. Project. Pike Island Locks and Dam, Ohio River. Tests were conducted by the USAE Ohio River Division.

3. Purpose. To develop laboratory and field correlation and criteria for determining in situ shear strength.

4. Location of Test on Project Site. A shallow pit located in the main lock chamber.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested, The material tested was an indurated clay, medium hard, multi- slickensided with orientation of slickensides random. Ten-in-high specimens with 1 by 1 ft bases were sawn from ,!moundsM with a 20-in. power chain saw.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. In situ conditions were preserved as near as possible by placing wet burlap over the specimens. The shear rig was placed over the speci­ men and did not require outside reactions for applying the shear load. Hydrostone was poured on the specimen's upper surface and between the specimen and wall of the shear rig. Loads were produced by 30-ton- capacity hydraulic jacks. Steel rollers were used to reduce friction at the normal load application point. The failure plane was always located approximately 5 in. above the bottom of the specimen. Hori­ zontal shear load was applied in increments of 300, 500, and 1000 lb. Shear load increments were added when deformation slowed to 0.001 in./min. Average stress rate varied from 1.25 to 2.34 psi/min.

Vertical displacements were not measured; however, shear displacements were measured with dial gages of 0.001 in. accuracy. The maximum shear stress failure criterion was used. Failure corresponded to that shear load which caused continuous displacement. Displacement rates were not held constant during each test. Average displacement rate was 0.0046 in./min.

7. Test Results, Conclusions, and Comments. Shear took place along slickenside planes for some specimens and through the intact materials for others. The shear surfaces were irregular. Normal stress varied from 25 to 92 psi with corresponding shear failure occurring at stresses of 40 and 135 psi. The largest horizontal displacement at which failure occurred was 0.24 in. Times to failure ranged from 24 to 48 min. A Mohr-Coulomb failure envelope was determined, 0 = 28 deg and c = 25 psi.

E13 Laboratory direct shear tests on 6-in.-diam cores resulted in 0 = 35 deg and c = 40 psi. The laboratory stress rate was 50 psi/min, which was much higher than field stress rate.

E14 CASE HISTORY NO. E -9

1. Reference, Kenty and Meloy (1965)

2. Project. Belleville Locks and Dam, Ohio River. Tests were conducted by the USAE Ohio River Division.

3. Purpose. To develop laboratory and field correlation and develop criteria for determining in situ shear strength.

4. Location of Test on Project Site.

Test series A. Inside an 18-ft-deep pit located in the center of the main lock chamber.

Test series B. Inside a shallow pit in the floor of an auxiliary lock chamber.

5. Preparation and Characteristics of Intact Mated, als or Discontinuity Tested.

Test series A. Indurated clay, medium hard, multislickensided. Material was a little more dense than that at Pike Island (Case History E-8) .

Test series B, Soft to medium hard claystone, transitional between a massive indurated clay and laminated clay-shale. Slickensides were essentially horizontal and spaced at 1/8 in. or less. All specimens were the same size and formed in the same manner as those at Pike Island.

6. Test Conditions. Loading Procedures. Rate of Loading, and Failure Cri­ teria. Loading apparatus was identical to that at Pike Island. Shear load was added in increments of 500 lb with increments being added when deformation slowed to 0.001 in. in 3 min. Average stress rates were: Test series A - 0.65 to 0.8 psi/min; Test series B - 0.19 to 0.8 psi/min. Failure criterion was the same as that of Pike Island. Average displace­ ment rate was 0.0007 in./min.

7. Test Results, Conclusions, and Comments.

Test series A. Shear mostly took place along the slickensides, leaving an irregular surface. Shear also took place through the intact material for some specimens. Normal stress varied from 23 to 91 psi with corre­ sponding shear failure at 50 and 110 psi. Shear strength parameters were 0 = 40 deg, c = 20 psi. The largest horizontal displacement at which failure occurred was about 0.12 in. Times to failure ranged from 54 to 169 min. Laboratory results of direct shear tests on 6-in.-diam

E15 cores were widely scattered but generally indicated higher strength than that measured in the field.

Test series B, Shear planes were slightly undulating and along the slickensides. Normal stress varied from 52 to 129 psi with corresponding shear failure stresses of 55 and 25 psi. Shear strength parameters were 0 = 43 deg, c = 0. Largest horizontal displacement at failure was about 0.16 in. Times to failure ranges from 140 to 279 min. Field results fell within widely scattered laboratory results from direct shear tests on NX-size cores.

For test series A and B, the laboratory stress rate was equal to 50 psi/min.

E16 CASE HISTORY NO. E-10

1. Reference. Kenty and Meloy (1965)

2. Project. Cannelton Locks and Dam, Ohio River. Tests were conducted by the USAE Ohio River Division.

3. Purpose. To develop laboratory and field correlation and develop cri­ teria for determining in situ shear strength.

4. Location of Test on Project Site. Undisturbed chunks were obtained from the lock area and moved to a nearby test site.

5. Preparation and Characteristics of Intact Material or Discontinuities Tested. Material tested was a calcareous compaction shale, soft to medium hard, highly fissile, with thin horizontal laminations. Speci­ mens were placed on a prepared limestone surface.

Test series A - Eighteen specimens were sheared in a direction parallel to the bedding. Test series B - Eight specimens were sheared perpendic­ ular to the bedding. All specimens were 10 in. high with 12 by 12-in. bases.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. Loading apparatus and failure criteria were the same as those used at Pike Island Lock and Dam (Case History E-8) . Loading procedure was the same as that used at Belleville Lock and Dam (Case History E-9). Average shear stress rates were: Test series A, 0.3 to 0.99 psi/min; Test series B, 0.19 to 0.9 psi/min. Average displacement rate for series A and B was 0.0007 in./min. Failure criterion identical to that used at Pike Island.

7. Test Results, Conclusions, and Comments.

Test series A, Sheared surfaces were smooth, horizontal, and along the laminations. Field results were contained in a broad band of laboratory direct shear results on 6-in.-diam cores. Shear strength parameters were 0 = 14 deg, c = 40 psi. Largest horizontal displacement at failure was 0.1 in. Times to failure ranged from 44 to 288 min.

Test series B. Sheared surfaces were horizontal and relatively smooth. Normal stress ranged from 27 to 156 psi with corresponding shear failure stresses of 60 and 110 psi. Shear strength parameters were 0 = 17 deg and c = 50 psi. Largest horizontal displacement at failure was 0.3 in. Times to failure ranged from 79 to 409 min. Laboratory direct shear

E17 results on 4 by 4 in. prismatic specimens agree with field results; however, only three laboratory tests were conducted perpendicular to the bedding.

Since these specimens were cut out and moved, they were subject to large amounts of disturbance and could have been tested in the laboratory (comment).

E18 CASE HISTORY NO. E-ll

1. Reference. Krsmanovic and Popovic (1966)

2. Project. Grancarevo Dam, Yugoslavia

3. Purpose* To measure the shear strength along various discontinuities.

4. Location of Test on Project Site. The tests were performed in adits and tunnels.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Discontinuity Tests - Limestone test blocks had base dimen­ sions of 9.2 by 5.9 ft (area = 54 sq ft). To prevent specimen disturbance, manual excavation was used with a limited amount of explosives. Tests were conducted on (1) clean fissures, (2) fissures up to 1 mm in thickness filled with detrital material, and (3) fissures containing clay layers up to 20 mm thick. Test blocks were encased in concrete and steel frames.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. Normal and shear loads were applied by hydraulic jacks of 1500- and 3000-metric-ton capacity. An inclined shear stress was applied after consolidation. Displacements were measured, vertically and in the direction of shear. Maximum shear stress failure criterion was used. After initial failure, the blocks were resheared under new normal loads.

7. Test Results, Conclusions, and Comments. Test duration ranged from 20 to 30 hr. Consolidation pressures used were 0.0, 71, 213, and 350 psi. Normal stresses active during shear were not necessarily the same as the consolidation pressures. A maximum normal stress of 350 psi was applied during shear. Displacements varied across the length of the specimens with displacement in the shear direction being greatest near the shear load application point. The maximum displace­ ment presented was about 2 in.

Uneven surfaces exhibited greater strengths than smooth surfaces. Shear strength decreased as the fill material thickness increased. Tests on filled discontinuities resulted in Mohr failure envelopes which were initially steep, then begin to flatten out, followed by later steepening of the Mohr envelope at high normal loads.

E19 Very approximate shear strength parameters can be determined by drawing straight lines through the test data. Actual failure envelopes were curves.

(1) clean fissures: 0 = 37 deg, c = 112 psi (2) thin filled fissures: 0 = 38 deg, c = 28 psi (3) thick filled fissures: 0 = 15 deg, c = 14 psi

At high normal loads the shear strength of the fill material has less effect on the joint shear strength since as the fill material is com­ pressed more shear resistance is contributed by the irregularities. This may account for the steepening of the Mohr envelope at high normal loads (comment) .

E20 CASE HISTORY NO. E-12

1. Reference. Uriel (1966)

2. Project. Renegado Dam, Ribarroja Dam and Santomera Dam. Tests were conducted by Transportation and Soil Mechanics Laboratory, Spain.

3. Purpose. To obtain the shear strength of rocks located in areas from which it is difficult to obtain laboratory specimens.

4. Location of Test on Project Site, Tests were performed in trenches.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. Renegado Dam - calcareous marl; Ribarroja - joints in marl which were filled with fibrous gypsum ranging in thickness from 1 to 4 in.; Santomera - argillaceous marl. The test blocks had base dimen­ sions of 20 by 20 in. (area = 3 sq ft). After each block was formed, a shallow ditch was dug along its base. The ditch was filled with bentonite and concrete. Test blocks were each encased in a steel frame with concrete placed between the blockfs sides and frame, while sand was placed between the cover plate and the block's upper surface.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The blocks were saturated by supplying water under pressure, through a hole in the cover plate. Pressure saturation took place for a period of several days to two months. After saturation, the water pressure and vertical jack stress were reduced an equal amount to main­ tain a constant effective stress. The horizontal or inclined shear load was applied in stages until failure. At Ribarroja and Santomera, tests were also conducted while the material was at its natural moisture content rather than saturated. No information on the failure criteria.

7. Test Results, Conclusions, and Comments.

Renegado - Under complete saturation: 0 = 36 to 49 deg, c = 26 to 62 psi Ribarroja - Under complete saturation: 0 = 28 deg, c = 23 psi. Natural moisture conditions: 0 = 29 deg, c = 21 psi Santomera - Under complete saturation: 0 = 38 deg, c = 10 psi. Natural moisture conditions: 0 = 41 deg, c = 51 psi.

E21 CASE HISTORY NO. E-13

1. Reference. Ruiz et al. (1968)

2. Project. Solteiria Dam, Brazil.

3. Purpose. To determine the foundation shear strength.

4. Location of Test on Project Site. Majority of tests were conducted in exploratory shafts.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The materials tested were vesicular basalt, amygdaloidal basalt, and jointed basalt. Twenty-one blocks were tested, each having base dimensions of 2.3 by 2.3 ft (area = 5.3 sq ft).

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The normal load was provided by cable anchoring. The 15-deg inclined shear load was produced by hydraulic jacks. The blocks were initially failed and then repeatedly sheared 146 times under various normal loads. Maximum shear stress failure criterion was utilized.

7. Test Results, Conclusions, and Comments. Initial failure of each block yielded Mohr-Coulomb shear strength parameters of 0 = 42 deg and c = 26 to 34 psi. The failure envelopes were actually curved. By plotting log shear stress versus log normal stress and fitting the data to a straight line, a curved shear envelope can be defined by an equation of

the form t = Acr^ where r = shear strength, A = a constant, K = a constant, and cr = normal stress. Results of the initial tests on each n

block can be defined by t = 1.87a^*^(kg/cm^).

E22 CASE HISTORY NO. E-14

1. Reference. Serafim and Guerriero (1966) and (1968)

2. Project. Gran Suarna Dam, Spain

3. Purpose. To obtain the foundation shear strength

4. Location of Test on Project Site. Tests were performed in tunnels and adits located across the dam foundation.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The rock tested was a jointed quartzite containing alternating layers of schistose quartzite. Eight blocks were sheared along joint surfaces and eight other blocks were sheared transverse to the jointing or foliation. The base dimensions of the test blocks were 2.3 by 2.3 ft (area = 5.3 sq ft) .

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The specimens were tested at their natural moisture conditions, which were close to saturation. Single-jack loading was used; that is, the same jack applied both the normal and shear loads. Therefore, the normal and shear loads were increased simultaneously. The maximum shear stress failure criterion was utilized. Displacements were measured vertically and in the direction of shear.

7. Test Results, Conclusions, and Comments.

Shear along discontinuities with partial clay filling: 0 = 41 deg, c = 90 psi. Shear along discontinuities with complete clay filling: 0 = 31 deg, c = 30 psi. Shear transverse to jointing through intact rock: 0 = 53 deg, c = 90 psi. Measured shear strength was somewhat greater where a portion of intact rock was sheared beneath the test blocks.

E23 CASE HISTORY NO. E-15

1. Reference. Serafim and Guerriero (1968)

2. Project. Las Portas Dam

3. Purpose. To determine the shear strength of critically located discon­ tinuities.

4. Location of Test on Project Site. Tests were carried out in adits and tunnels.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The materials tested were described as (1) a siliceous schist with the foliation parallel to the bedding planes and (2) a rock mass with a system of joints containing thin clay fillings spaced 3 to 12 ft apart. Base dimension of specimens: 2.3 by 2.3 ft (area = 5.3 sq ft). No other information.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. Single jack loading was utilized as described in Case History E-14. Four blocks of (1) and (2) above were tested, each at a different normal load in order to obtain Mohr-Coulomb failure envelopes. Maximum shear stress failure criterion was employed.

7. Test Results, Conclusions, and Comments.

Clay-filled joints: 0 = 38 deg, c = 46 psi Schistocity plane: 0 = 40 deg, c ** 10 psi

E24 CASE HISTORY NO. E-16

1. Reference. U. S. Army Engineer District, Fort Worth, Texas (1961)

2. Project, Proctor Dam Site on Leon River about 8 miles northeast of Comanche, Texas.

3. Purpose. Results were to be used in the spillway design and to evaluate the reliability of results from laboratory direct shear tests.

4. Location of Test on Project Site. Shale located some distance from the spillway foundation was tested; however, laboratory tests on undis­ turbed samples revealed that this shale was similar to that located in the spillway area. Tests were conducted in trenches located to require a minimal amount of excavation.

5. Preparation and Characteristics of Intact Materials or Discontinuity Tested. The top few inches of the shale was badly weathered, however underneath the shale becomes quite hard. The shale tested was at a depth of 10 ft below the original ground surface and contained a few iron concretions ranging from pebble size to 1 ft in diameter. It was not a fissile shale and did not contain any pronounced laminations. Concrete blocks cast on leveled shale surfaces were also tested. The shale blocks were formed with a small power chain saw. Concrete and shale blocks were 1-ft high having base dimensions of 3 by 3 ft (area = 9 sq ft) . A steel shear box was placed over each specimen and grouted in place.

6. Test Conditions, Loading Procedure, Rate of Loading, and Failure Cri­ teria. The natural moisture content of the shale was preserved with a coating of latex, which was removed just before testing. After applying the normal stress, the specimens were flooded and water was maintained over the failure plane throughout each test. The normal stress was measured by a Baldwin-type load cell and applied by a hydraulic jack reacting against a weighted structural bridge. Rollers were placed between the normal load jack and loading plate to reduce friction. The normal stress was applied as rapidly as possible and maintained for 24 hr before applying the shear stress. The horizontal shear load was applied by 50-ton-capacity hydraulic jacks reacting against the trench wall. Vertical and horizontal displacements were measured with Ames dial gages. Shear load increments were applied at equal time intervals resulting in stress rates of:

E25 Shear Load Increment Type of Block Test psi/min Remarks Shale i 0.032 Load accelerated late in test 2 0.027 3 0.029 Concrete on shale C-l 0.014 C-2 0.012 C-3 0.038

Maximum and residual shear stress failure criteria were used.

Test Results , Conclusions, and Comments.

Shale block tests: 0 = 14 deg, c = 14 psi (maximum ;shear stress criterion).

Shear Average Shear Normal Stress Time to Displacement Stress at Failure Displacement, in. Failure Rate Test psi psi Shear Vertical hr in./min i 7 15 0.06 0.025 up 11.5 0.00009 2 28 20 0.14 0.06 up 12 0.00019 3 43 24 0.3 0.04 down 14 0.00037

Concrete block tests: 0 = 18 deg, c = 14 psi (maximum shear stress criterion). Failure occurred within the shal 1/2 in. or less below contact •

Shear Average Shear Normal Stress Time to Displacement Stress at Failure Displacement, in. Failure Rate Test psi psi Shear Vertical hr in. /min C-l 7 17 0.15 0.12 down 21 0.00012 C-2 28 24 0.15 0.05 down 25 0.0001 C-3 43 28 0.10 0.05 down 14 0.00012

The residual stress was actually never attained, but residual shear parameters were given as follows: shale blocks 0 = 14.5 deg, c = 5.7 psi; concrete blocks 0 = 12 deg, c = 11 psi. Author's attribute the slightly greater strength measured in concrete block tests to the

E26 removal of moisture from the shale during the concrete’s hydration. The shale was thus hardened immediately below the contact.

Laboratory direct shear tests were conducted in shale samples from adjacent to field test blocks. The laboratory cohesion intercept c was slightly less and friction angle 0 was slightly greater than that determined in the field; laboratory values were used in design. The sliding friction or residual strength as determined from laboratory direct shear tests were not used in design since failure occurred along the concrete-shale contact, unlike the field tests where failure occurred within the shale. CASE HISTORY NO. E-17

1. Reference. Wallace et al. (1969)

2. Project. Auburn Dam, California. Studies conducted by the U. S. Bureau of Reclamation.

3. Purpose. To obtain shear stress/displacement relationships and the foundation shear strength.

4. Location of Test on Project Site. Tests were conducted in tunnels and adits.

5. Preparation and Characteristics of Intact Material or Discontinuity Tested. Joints, shear zones, and foliation surfaces were tested; however, results were only given for a test on a single foliated amphibolite specimen. Eight-in.-high test blocks with 15 by 15 in. bases (area = 1.6 sq ft) were cut with a diamond saw and hand chipping and were encased in a metal frame. Mortar was placed between the frame and test block.

6. Test Conditions. Loading Procedure. Rate of Loading, and Failure Cri­ teria. The normal and shear loads were applied by 200-ton-capacity hydraulic jacks. Spherical bearing blocks transmit the loads to the test block. The shear load was inclined 10 deg and applied at a stress rate of 25 psi/min. Horizontal and vertical displacements were measured by linear variable differential transformers (LVDT's) and dial gages. The displacements were continuously recorded on electronic plotters. The failure criteria were the maximum and residual stress criteria.

7. Test Results, Conclusions, and Comments. The block was sheared under the following sequence of normal loads: 400, 100, 300, 500, 700, and 1000 psi. Under 400 psi, the block reached a maximum shear stress of 1400 psi at less than 0.01-in. displacement in the shear direction. Under the final normal stress of 1000 psi, horizontal displacement reached 0.04 in., which was not considered large enough to produce residual strength values. Test results can be approximated by a straight-line failure envelope where 0 = 41 deg and c = 80 psi.

E28 Unclassified Security Classification DOCUMENT CONTROL DATA - R & D (Security classification o^ittej_body^oi_abstract_and_indej(ing_annotation_tiw

. ORIGINATING a c t i v i t y (Corporate author) r2*. REPORT SECURITY CLASSIFICATION Unclassified U. S. Army Engineer Waterways Experiment Station 2b. GROUP

3. R E P O R T T IT L E

IN SITU TESTS FOR THE DETERMINATION OF ROCK MASS SHEAR STRENGTH

4. DESCRIPTIVE NOTES (Type of report and inclusive dates) Final Report 5- AUTHOR(S) (First name, middle initial, last name) Timothy W. Zeigler

6. R E P O R T D A TE 7 a . T O TA L NO. O F PAGES 76. NO. O F REFS November 1972 206 118 8a. CONTRACT OR GRANT NO. 9a. ORIGINATOR’S REPORT NUMBER(S)

Technical Report S-72-12 6. PROJEC T NO.

96. OTHER REPORT NO(S) (Any other numbers that may be assigned this report)

0. DISTRIBUTION STATEMENT

Approved for public release; distribution unlimited

1. SUPPLEMENTARY NOTES 12. SPONSORING * I LI T ARY A C T IV IT Y

Office, Chief of Engineers, U. S. Army Washington, D. C.

13. ABSTRACT Rock shear strength is often determined from in situ tests. Many cases have been reported in the literature describing in situ shear test procedures and test results. The purpose of this report is to summarize this information for guidance in planning and evaluating such tests. The types of tests dis­ cussed are: (1) direct shear test, (2) triaxial or multiaxial test, (3) torsion shear test, and (4) pull-out test. The direct shear test is most widely used, and some 48 case histories of such tests are summarized in Appendixes A through E. The main advantage of the direct shear test is the ability to measure the shear resistance in any desired direction along potentially critical discontinuities. The test is also popular due to its adaptability to field conditions; tests can be conducted in trenches, adits, tunnels, and even calyx drill holes. Direct shear tests have been carried out on clean and filled discontinuities, intact materials, and concrete-on-rock contacts. Specimen size, types of encasements (when used), loading procedures, and test moisture conditions are varried. Instrumentation is generally provided for measuring horizontal and vertical displacements. Illustrations of various direct shear test setups that have been employed are presented. Failure envelopes determined from in situ direct shear test results reported in the literature were generally straight lines defined by Mohr-Coulomb shear strength parameters 0 and c . Average peak strength parameters are given below:

Test Zone Average 0, deg Average c, Clean discontinuities 39 24 Filled discontinuities 30 23 Intact rock 50 70 Concrete-on-rock contacts 38 40

As expected, intact specimens exhibited the greatest average shear strength, and filled discontinuities the least.

FO RM REPLACES DD FORM 1473, 1 JAN 64, WHICH IS DD NOV 65 I / W OBSOLETE FOR ARMY USE. Unclassified Security Classification Unclassified Security Classification

14. LINK A LINK B LINK C KEY WORDS ROLE WT ROLE W T ROLE WT

Field tests Rock masses Rock tests Shear strength Shear tests

Unclassified Security Classification