University ox Nevada - Reno Reno Reno, Key; ;v5 57

geology, Geotechnical Properties and

Vesicular Rock Classification of 1onsetown

Basalts and Latites, Truckee Area, California

A thesis submitted in partial fulfillment ox the requirements for the degree of Master of Science

in Geological Engineering

far L J

Joseph G. Franzone

May 1980 HftWttiS U M A I 'f

fj'h.i s thesis of Joseph 0. Iran zone is approved:

University of Revada. Reno

May 19B0 ii

ACKNOW LEBGEMENT 3 I am indebted to several people for the assistance

and encouragement they gave me dui’ing the preparation of

this thesis. Professional advisement of the project and

critical reviewing of the manuscript were provided by Sr. Robert J. Watters, Dr. Joseph Lints, Jr. and Dr. Y. S. Kim.

Dr. Y. S. Kira graciously made the Rock Mechanics Laboratory and testing equipment available. Dr. Robert J. Watters

also allowed unlimited freedom to the Geological Engineering

Laboratory equipment and also, along with Dr. Joseph Lintz, Jr., provided invaluable guidance throughout the

thesis preparation. Appreciation for help in de-bugging the laboratory equipment goes to my colleague, Ken Krank.

Finally, and most importantly, I am indebted to my parents who, whenever I needed them, were always present and

supportive. ABSTRACT Geology, physical and engineering properties of the rock units of the lousetown Basalts and Latites in the Trucked Area, California were determined by field and laboratory testing and field ODservations.

Of the 16 properties that were calculated for massive samples, 8 were shown to be capable of preuicting i^-e compressive strength and 10 were shown to be capable of predicting the Elastic Modulus. for vesicular samples, an unusually drastic strength reduction was shown to accompany decreasing specific gravity. As an aid m the prediction oi engineering properties of vesicular samples: (1) a- graph was evolved to correlate Schmidt Rebound Value

(a measure of the competency of a rock sample; to the compressive strength via porosity and/or specific gravity, and (2) a classification system was devised to relate general engineering properties of vesicular rocks to their competency, porosity and/or specific gravity. CONTENTS SIGNATURE PAGE...... i ACKNOWLEDGEMENTS...... ii ABSTRACT...... --- ...... --- ... ill

- SECTION ^Introductory Material......

Purpose and Method of Investigation...... 2 Physical Setting and Accessibility..... 4 Climate and Vegetation...... 8 Previous Investigations...... 10 SECTION II-Geology Regional Sierra Nevada...... 1 2 Basin and Range Structure...... 13

Local Local Geology...... *...... 15 Local Structure...... 18

Lousetown Basalts and Latites...... 22 Correlation and Age...... 22 Volcanic Rock Classification...... 25 Mineralogy...... 26 Alder Hill Basalt...... 28 Dry lake and Boca Ridge Plows.... . 30 Polaris Olivine Latite...... 31 Big Chief Basalt...... 31 Bald Mountain Olivine Latite...... 33 Tahoe City Olivine Latite,...... 34 Hirschdale Olivine Latite...... 38 Ploriston Olivine Latite...... 43 Structure and Faulting...... Summary of Truekee Area. Events......

Description of Flow Structure...... 47 Rock Weathering...... 60 SECTION Ill-Physical and Engineering Properties of Rock Units...... 6 5

Introduction. * ♦ * «> ♦ e f * * » 66 Previous y/ork 70 Use and Importance of Engineering Properties. 71 Physical and Engineering Properties of ?town Basalts and Latites.... 73 Alder Hill Basalt...... 73 Big Chief Basalt...»...... 75 Bald Mountain' Olivine Latite...... 76 Tahoe City Olivine Latite...... 80 Hirschdale Olivine Latite...... 83 SECTION IV-Physical and Engineering Properties Determination...... *...... 86 Uniaxial Compressive Strength...... 87 Uniaxial Compressive Strength Testing...... 93 franklin Point Load Strength...... 96 Franklin Point Load Strength Testing...... 99 Apparent Specific Gravity-Apparent and True Porosity...... 100 Schmidt Hammer Test...... •• 10n Ultrasonic Wave Testing...... 105 Elastic Constants...... 1 "'O Dynamic Elastic Constants Determination..... 114 Static Elastic Constants Determination--- * DrillaLility...... 5 ’ -i -o Characteristic Impedance......

SECTION V-Rock Property Relationships and Vesicular Rock Classification......

Rock Property Relationships...... Strength of Vesicular Basalts...... • • Vesicular Rock Classification...... '->) Conclusion...... - • * •1 JO SECTION VI-Appendix Geologic Time Scale...... Unified Soil Classification System

REFERENCES 162 PHOTOS

Photo 1 Upper Truckee River Canyon. View South from atop the Bald mountain Olivine T.n+. it.p ......

Photo 2 Tertiary Andesite of Big Chief Mountain, Upper Truckee River Canyon Looking North...... 16

Photo 3 Tertiary Andesite on Planks of Sawtooth Ridge, Upper Truckee River. Canyon.... .17

Photo 4 Crystals of analcite in vesicles of Alder Hill Basalt......

Photo 5 Outcrop of Polaris Olivine Latite, 1-1/2 miles east of Truckee, California.... .32

Photo 6 Mosses and Lichens on Bald Mountain Olivine Latite...... 32

Photo 7 Talus slope of Tahoe City Olivine Latite along the Upper Truckee River Canyon 2 miles north of Tahoe OiXy, CA..,.. . *36

Photo 8 Weathering stain on Tahoe City Olivine 37

Photo Columnar jointing, Hirschdale Olivine 9 .37

Photo 10 Scoria from source of Hirschdale Olivine T.qt.vhp rrtl...... 40

Photo 11 Scoria from source of Hirschdale Olivine T,nt it. p ...... 41

Photo 12 Sha-Neva, Inc. workings near the source vent of Hirschdale Olivine Latite.... 42

Photo 13 Light-weight aggregrate near source vent of Hirschdale Olivine Latite.... . 42

Photo 14 Highly weathered Ploriston Olivine Latite exhibiting platy parting...... 44

Photo 15 PIow structure of Hirschdale Olivine . .68

Photo 16 Plow structure of Bald Mountain Olivine o ■*48 VIX

Photo 17 Plow structure of Bald Mountain Olivine Latite...... 50

Photo 18 Plow contact in Hirschdale Olivine Latite..52

Photo 19 Entablature of Bald Mountain Olivine Latite...... • 53

Photo 20 Catem.i-llar Thread” type of basal 'structure in Bald Mountain Olivine Latite...... 55

Photo 21 Vesicular flow top...... 56 Photo 22 Plow contact in Bald Mountain Olivine Latite...... 57

Photo 23 Plow contact in Hirschdale Olivine Latite..58

Photo 24 Spheroidal weathering on lower talus slopes of Tahoe City Olivine Latite...... 51

Photo 25 Blocky appearance of Bald Mountain Olivine Latite along Upper Truckee River---

Photo 26 Conical failure surfaces of rock sample after compressive strength test showing powdering and abrasion...... 89

Photo 27 failure plane of glassy Big Chief Basa.lt sample after compressive strength test failure angle is 46°...... 90

Photo 28 Compressive strength testing apparatus.... 94

Photo 29 Sample of Bald Mountain Olivine Latite in loading device after compressive stx'ength test...... 95

Photo 30 franklin Point Load Testing Apparatus..... 98

Photo 3 i Schmidt Rehound Value. .'...... 103 Photo P wave and S wave traces on oscilloscope...... 106

Photo 33 Ultrasonic Pulse wave testing apparatus.-... 107

Photo 34 Strain gages mounted on rock samples

Photo 35 Static Elastic Constants testing apparatus...... 118 V 11 J.

GRAPHS

Graph A-1 Compressive Strength vs. Porosity...... 130 Graph A-2 Compressive Strength vs. Schmidt Rebound Value, ...... 131

Graph A-3 Compressive Strength vs. P wave Impedance...... 131

Graph A--4 Compressive Strength vs. P wave Velocity...... 132

Graph A-5 Compressive Strength vs. Specific Gravity...... 133

Graph A--6 Compressive Strength vs. 3 wave Velocity...... ^ 34

Graph A~7 Compressive Strength vs. Drillability.... Graph A-8 Point Load Index vs. Compressive Strength...... 135

Graph A-9 Elastic Modulus vs. S wave Velocity...... 135 Graph A-10 Elastic Modulus vs. P wave Velocity...... 136

Graph A-11 Elastic Modulus vs. P wave Impedance..... 136

Graph A-12 Elastic Modulus vs, S wave Velocity..... 137

Graph A-13 Elastic Modulus vs, P wave Velocity.... .138

Graph A-14 Elastic Modulus vs. Porosity...... 138

Graph A-15 Elastic Modulus vs. Specific Gravity..... 139 Graph A-16 Elastic Modulus vs. Schmidt Rebound Value,...... 139

Graph A-17 Elastic Modulus vs. Drillability...... 140

Graph A-18 Elastic Modulus vs. Point Load Index.... 140

Graph A-19 Compressive Strength vs. Elastic Modulus.141 Graph A*-20 Compressive Strength vs. Elastic Modulus.142

Graph A-21 Attenuation vs. Specific Gravity...... '43 IX

Graph A-22 Attenuation vs. Porosity...... K 3

Graph A-23 -Drillability vs. Specific Gravity...... H4

Graph A-24 Drillability vs. Porosity...... 144

Graph A~25 P wave Impedance vs. Porosity...... H5 Graph A~26 P wave Velocity vs. Schmidt Rebound • Value...... V --- 145

Graph A-27’ Ratio of P wave to S wave velocities vs. Specific Gravity for Vesicular Samples, Samples with cracks and Massive Samples...... 1 Graph A--28 P wave Velocity vs. Specific Gravity 147 Graph A~29 Compressive Strength vs. Specific Gravity with predicted and actual Compressive Strength curves......

Graph A-30 Classification of Vesicular Basalts by Reduction of Compressive Strength and Specific Gravity...... 153

Graph A-31 Prediction of Compressive Strength of Vesicular Basalt by Porosity and/or Specific Gravity via Schmidt Rebound V aiue ...... 1 5 4 X

FIGURES

Fig. 1 Physiographic Map of the Truckee. River Area and the.Truckee River System...... • 5

Fig. 2 Map Showing Extent of the Lousetown ?fyT,mati nn in Truckee Are a...... 6

Fig. 3 Stratigraphy of the Truckee Area, CA...... 19 Fig. 3 A Sequence of Lousetown Formation flows in the Truckee Area, - CA...... 24

Fig. 4 Chemical Analysis of Lousetown Flows Compared with Chemical Analysis of Basalt, Andesite and latite...... 27

Fig. 3 Idealized Cross-section of Lousetovn Formation Flows...... 49

Fig. 6 Changes in pH values with Increased Weathering of Basalt...... 63

Fig. 7 Shear and Normal Stresses Acting on Failure Plane at Failure Angle...... 91

Fig. 8 Schematic of Pulse Wave Testing Apparatus... 108

Fig. 9 Loading Induced Strain...... 112

Fig.- 10 Strain Gage Attachment ...... 119

Fig. 11 Stress-Strain Testing Apparatus 120 TABLES

Table 1 Joint Spacing for Rock...... 68

T abl e 2 Strength Glassification for Rock...... 68 68 Table .5 Permeability of Rock Masses------T-abl e 4 Rock Weathering Classification...— .. .69 Table 5 Test Results on Rock Samples from the Lousetown Formation. ..123

Table 6 Test Results on Rock Samples from the Lousetown Formation (cont.)...... 124

Table 7 Test Results on Rock Samples from the Lousetown Formation (cont.)..... 125

Table 8 Classification of Vesicular Basalts According to their Engineering Properties...... 155 XIX SYMBOLS A =cross-sectional area cC ^failure angle from compressive strength testing AP ^apparent porosity ASG -apparent specific gravity B =v;ave attenuation through sample D _ -drillability E ^Elastic or (Young's) Modulus G -strain G =Modulus of Ridigity (or Shear Modulus) g --acceleration due to gravity 'O =unit weight I =Point Load Strength index j , -Corrected Point Load Strength Index s(50) K -Bulk (or Compressibility) Modulus k -p erm e ab il it y n --porosity n ^electrical resistance P -applied load Phi =P wave impedance q -unconfined, uniaxial compressive strength -a r -coefficient of correlation Sc -unconfined, uniaxial compressive strength SG ^specific gravity (as determined from ASG equations) C -normal stress SRV =Schmidt Hammer Rebound Value S^ -tensile strength s u b s c r i p t ^ =dynamically determined value subscripts N=statically determined value l -shear stress u -Poisson's Ratio V =P (longitudinal) pulse wave velocity P V s =S •(transverse) pulse wave velocity V -j gg-P^lse wave velocity SECTION I Introductory Material £r i

PURPOSE AND MET HO 3) OF INVESTIGATION This study of the flow units of the Lousetov/n

Formation was conducted for the following reasons: (t) to determine the geology of the individual flow units, (2) to - determine the physical and engineering properties of the different flow units, both horizontally and vertically,

(3) to be able to predict, from field index and simple

laboratory testing, other intrinsic engineering properties

of the units which could otherwise only he derived through

extensive laboratory preparation and testing, (4) to devise

a useful classification system for vesicular rocks to be

able to accurately predict their engineering properties

from the same field index testing methods mentioned previously, and (5) to acquaint the author, in a general way, to the determination, reliability and applications

of engineering testing procedures„

A period of Summer and Fall, 1979, was devoted to field mapping, sample collection and field and labor­ atory testing. Mapping was accomplished by field checks

of all flow boundaries, aerial photographs to correctly

delimit these boundaries and correlation of the author's

observations with already existing geologic maps, specif­

ically: Lindgren ( 1897) , Daley and Poole ( 1949), Burnett

and Jennings (1962), Birkeland ( 1.963), Thompson and White

( 1964), Matthews ( 1968) and Burnett (1971). 7his map, which contains both geologic and engineering properties data is contained in the map pocket. Rock sample location, preparation and testing procedures are described in Physical and.Engineering Properties of -Rock Units. 4

PHYSICAL SETTING AND ACCESSIBILITY The Truckee River Area lies in the north-eastern part of the Sierra Nevada Physiographic Province. The main features are two north-trending mountain ranges, the 9,100 ft. high Sierra Nevada on the west and the 10,800 ft, high .

Carson Range on the east. Between which, lie two basins, the Truckee Basin to the north and the Tahoe Basin to the south. Between the Tahoe Basin (lake elevation 6,230 ft,, basin elevation 4,700 ft.) and the Truckee Basin (elevation

6,000 ft.) lias a 1,600 ft, deep canyon: the Upper Truckee River Canyon 'which is cut through Tertiary Andesites and Quaternary Basalts, The canyon is a straight, youthful canyon; devoid of a distinctive flood plain. The river crosses the Truckee Basin, then flows into the 2,700 ft. deep Lower Truckee River Canyon on its way through the Reno

Basin (4„400 ft.) to empty into Pyramid Lake (3,800 ft,);

(Pig. 1). The Quaternary Lousetown Basalt Formation that is researched in this study occurs along the Upper Truckee

River Canyon an d the Truckee Bas in (Pig. 2) from Tahoe City to Kir solid al Calif ornia. This includes the 15"minute quadrangles of North Tahoe, C3A-NV (1955) , Trucke e, CA-NY

(1939 ) and. V/est Mt „ :Rose, NY (19 55). The 1I ruclcee :River Are; a is access ible by an excellent network of r0 clds, Interstate 80 and the Southern Pacific 9

fig. 1 Physiographic map of Truck.ee River Area and Truckee River System 6

Fig. 2 Map showing extent of Lousetown Formation in Truckee Area 7

Railroad run along the Truckee River in the eastern part

of the study area, then continue westward when the river bends southward at Truckee. California State Highway 89

connects Truckee to Tahoe City along the Upper Truckee River Canyon. The lower slopes of the canyon are accessible

by many dirt roads; most are shown on topographic maps.

However, to explore the boundaries of all the flow units, the roads only helped to arrive in the general vicinity.

For most of the geological work, covering, many miles on

foot was the general rule. 8

CLIMATE AND VEGETATION The Upper Truekee River Canyon and the Truckee

Basin are located just east of the Sierran Crest. In this

area, the rain shadow effect is strinking. Soda Springs,

located 12 miles west of Truckee, CA, reports an annual precipitation of 45.64 in-. (115.93 cm). Going east, Truckee. has 26.13,in. (66.37 cm) and Reno reports 7.73 in. (19.63 cm)

(U. S. Dept, of Agriculture, 1941). The majority of the precipitation falls between November and March as snow

and rain. The tj'pe and density of vegetation in the Sierra are greatly affected by the precipitation gradient. Eir, pine and mountain hemlock grow to dense forest stands on the moderately steep slopes (Photo 1). In the lower slope areas 'of the Upper Truckee River Canyon, the forest thins out and is partly replaced by patches of manzanita. Sage­ brush and grasses are common throughout the alluvial floor of the Truckee Basin. m m

fl§| flilfelfSifi ■ •:•*•-' i";' :';;". ••-.;.... . ; .

$■*$<% mMi.

trill*VH '■ Je’Jf ** • %.! ' - : - ,V' - - ' ' V-ir

•; - C-':v

1 ' .. 1

Photo 1 Upper Trucjcee Rivei ^ canvon. View outh from atop the Bald Mountain Olivine laiite 10

PREVIOUS INVESTIGATIONS

There have been relatively few specific mentions of the Truckee Area Lousetown Basalts in the literature.

Lindgren (1897) was the first to map the general area, -Re did so in a very wide scope using no_differentiation to distinguish individual flows. Daley and Poole (1949) mapped the extreme western part of the study area. In 1962, Burnett and Jennings had finished compiling the Chico

Sheet for the California Division of Mines and Geology.

They used railroad company maps and understandably, many flow boundaries were in error. Birkland (1963) was the first to use any differentiation in the flow descriptions and he, with the aid of radiometric dates from D alrjcr.ple

(1964), evolved a chronology of the Truckee River, Louse- town Basalts and Eastern Sierra glacial events. Burnett (1971) mapped the extreme southern section of the study area near the northwestern portion of Lake Tahoe. There have been correlations of the Lousetown Basalts with the basalts which are found along the Sierran

Crest (Hudson, 1951), with the Warner Basalts in Plumas Co.,

California (Durrell, 1959) and even with the Cascade-type basalts in Oregon (Thayer, 1937). Although these associa­ tions seem tenable, conclusive evidence is lacking. SECTION II Geology REGIONAL GEOLOGY Sierra Nevada

Luring the Paleozoic Era arid extending into the

Mesozoic Era, the region now occupied by western Nevada and the Sierra Nevada was the site of a thick accumulation of marine sediments and volcanic rocks. This material, derived principally from continental sources to the east and volcanic sources to the west, was deposited in a basin near the margin of the continent. An episode of deformation caused these deposits to become highly deformed and faulted.

Approximately 130 million years ago, molten granitic rock was intruded into the sedimentary and volcanic rocks and caused further metamorphism. Intrusion lasted about 50 million years, ending near the end of the Cretaceous. During this period was an episode of gradual uplift and erosion which eventually wore away between 9-17 m

(15-27 km) of overlying rock, eventually exposing the granitic core of the present day Sierra Nevada. The Sierra uplift ceased during a period about

45 million years ago. At that time, the maximum elevation of the Sierra was between 3,000 and 5,000 ft. During this period, several rivers deposited gold-bearing gravels on the western flank of the exposed granitic core in central California. This period of quiescence was interupted approximately 30 million years ago with the onset of volcanic activity. Eruptions were mostly rhyolitic tuffs and ash flows which continued for about 10 million years 13

when it was replaced by andesite mudflows which ceased about 5 million years ago; succeeded by a period of

basaltic flows until 1.2 million years ago.

Before this, in late.Pliocene (Dalrymple, 1964), the Sierra began-to rapidly uplift and tilt westward.. This resulted in the gentle westward slope and abrupt

fault-bounded eastern escarpment. The uplift ceased 8 million years ago after the Sierra had attained its approx- imate present elevation.

During the last 2 to 3 million years, the crest of the Sierra has experienced several glaciations. Glaciers extended to elevations as low as 6,000 ft, on the east side; and as low as 3,000 ft, on the wetter western flank of the range. These periods of glaciation, which ended about 9,500 years ago, resulted in much of the spectacular scenery of the Sierra Nevada Range.

BASIN AND RANGE STRUCTURE Modern theories concerning the origin of the Basin end Range structural province can be grouped into two categories: (1) regional compression and (2) regional extension, With the onset of the plate tectonic theory, the latter seems to have more following by geologists and will be discussed, here.

The regional extension theory is best supported by Atwater (1970), Scholz and Barazangi (1971), Stewart

(1971) and Thompson and Burke (1974). Their work, based 14 primarily on plate tectonic theory and geophysical data, agree in the following respects.: (1) crustal extension due to faulting is oriented in a 'WNW-ESE direction, (2) the region has anomalously high heat flow and widespread volcanic activity, (3) studies of focal mechanisms of small earthquakes show a consistant 'direction of'extensions, and (4) the inception of Basin and Range faulting is dated at 15"-17 million years ago.

Based on this theory, it has “beer, suggested that the Basin and Range Province has undergone up to 180 mi'(300km) of extension (Hamilton and Myers, I960), thus increasing the width of the province by 30^. The extension would result in the formation of horst and graben structures. In the Pacific Northwest and the northwestern Great Basin, the onset of extension was accompanied by eruption of enormous volumes of basalt and salic tuffs and lava (Noble and Slemmons, 1975).- Extension and associ­ ated basaltic volcanism may result from a relatively abrupt change in direction of movement of the Pacific lithospheric plate relative to that of the North American plate (Noble, 1972). 15

LOCAL GEOLOGY The oldest rocks in the area are Jurassic and/or Triassic nietavolcanic rocks located along the crest of the Verdi Range,north of the thesis area. These rocks are characterized 'by metamorphosed tuff, breccia and other assorted flows specifically containing siliceous hornfelses. During Cretaceous time, medium-to coarse­ grained granitic rocks of the Sierra Nevada batholith were intruded into these inetavolcanic rocks (Larsen,

Gottfried, Jaffe and haring, 1954). Most of these granitic rocks were implaced along the present-day Sierran Crest; west of the thesis area. The Tertiary sequence consists mostly of volcanic rocks ranging from rhyolites to basalts. The older rocks

are;mostly Eocene pyroclastics near Conner Pass. Younger Miocene-Pliocene rocks are mostly andesite flows, int.ru- sives and tuff-breccias. The andesite tuff-breccias arc- limited to the Sierra Nevada and Carson Range. The andesite flows and ihtrusives are common in the Upper Truckee Canyon and Truckee Basin where they underlie or outcrop alongside of the Lousetown Basalts (Photo 2-3).

Much of the andesite carries phenocrysts of plagioclase, hornblende and pyroxene. In' some places, these rocks have been altered and either bleached or colored brightly

in reds and yellows, Occassionally, the altered rocks contain large amounts of silica. These andesite rocks are - m M i M m m m m m

:. '-VO;:Kv, •’;v- . V :- ■• ?-.' .. - ■>. ■

. ■ Sw^'4s* v .t,vy • ->>1/ ,•

:V-»..\s'Vt- «*.V? C-> «':'!■<

k .^ y'y w , ..• ,:ei .-^. m - /Vyjk\ . -. ■ ' •?:•■ r--»- ,«• V'., ••;; ^:- V*V- -aV -•* ’■ *....' ; •;:.' •

Photo 2 Tertiary ande site of Big Chief Mtn t Upper Truckee River Canyon looking nor 17

f tJ a s * ; m s)tt,'v.*4; w : mi ' '*vi

:

' ■ V :S -bV-V I) • " ' m w M s m m

Photo 3 Tertiary andesite on flanks of Sawtooth Ridge, Upper Truckee River Canyon 18 probably equivalent to the early Pliocene Kate Peak

Formation in western Nevada (Hudson, 1951) and the Mehrten

Formation in the northern Sierra (Curtis, 1954). The oldest Pleistocene unit is the Lousetown

Formation which is dominated by basaltic lava flows,but which, near Truckee, includes alluvium deposited upstream

from various lava dams which once blocked the Truckee River.

Pleistocene till and outwash are present along the river and the older of these units appears to post­ C date the Louse-town Formation in the Truckee area. The - t

till and associated outwash deposits are named, from oldest- |mu to youngest/; Hobart', Bonner Lake, Tahoe o.nd Tioga cu yt (Birkeland, 1964). The two older units lack moraine morph­

ology and are highly weathered, while the younger deposits 7 3

have well preserved morphology and are much less weathered. Recent deposits along the Truckee River consist

of river alluvium and colluvium, Truckee area stratigraphy is shown in Fig. 5. 1 o c al St me t ur e Despite evidence of a continuous, pre-andesite,

structural trough which includes Lake Tahoe Basin, Truckee

Basin and the Sierra Valley (.Lindgren 1896, 1897, 1911) t

present evidence now suggests m a t nosi. oone ma^or landforms of the Truckee area are a result of late Pliocene

(from 7.4-2.3 million years ago) faulting and wax ping o.vi.

the andesitic volcanism had occured (Dalrymple, 1964). 19 AVERAGE AGE FORMATION . LITHOLOGY THICKNESS

Recent 50 ft RECENT River and stream j Alluvium alluvium (15 m)

Quat. Lake Lake Led deposits ?.0 ft Deposits of Lake Tahoe (6 m)

Quat. .Moraines, glacial drift, 100 ft Glacial . fluvioglacial sand (50 m) Deposits. and gravel

Quat, Fluvial deposits of the 300 ft PLEISTOCENE Truckee Basin and Non-marine (91 m) Deposits Martis Yalley

Gravel, cobbles, silts Lousetown 50 ft and clays; mostly of (15 m) Formation- weathered andesite

Lousetown l 350 ft .Basalt and latite flows i(107 fa) Formation l Andesite to rhyolite 1600 ft PLIOCENE Mehrten or Kate Peak flows and Ihtrusives, (488 m) mudflow breccias

Granitic Granodiorites, granites, CRETACEOUS Intrusive tonolites and diorites; 7 Rocks Plutonic rocks

Meta- M e t av o 1 c an i c r o ck s, s 1 at e s, 7 TRIASSIC volcanic s tuffs and breccias

Fig 3 Stratigraphy of the Truckee Area, California 20

The Lake Tahoe Basin is a structural graben bordered on the east and west sides by north-south trending fault- scarps 5,000-6,000 ft. (1,525-1,830 m.) high. In addition, bench-ahd-slope topography on the east scarp suggests move­ ment along several closely-spaced parallel faults. The north and south bounding faults are less impressive but are still

1,300 and 3,500 ft. (395~-1»065 m.) respectively (Lindgren,

1896). Tilting has also occured in the. northwestern part of the Lake Tahoe Basin as shown by pre-Lousetown sands and gravels which dip 10°-16° east near the source of the Truckee

River (Birkeland, 1963). The Truckee Basin seems to have been formed by both faulting and warping. A 1,000-2,000 ft. (305-610 in.) north­ east-trending fault scarp delineates the southern border of the basin. The east and western boundaries are dissected, low-relief surfaces that are suggested of warping rather than faulting (Daley and Poole, 1949). The ridge separating the Lake Tahoe Basin frea the

Truckee Basin is probably a tectonic block, bounded north and south by faults (Birkeland, 1963) rather than a volcano as suggested by Lindgren (1897). furthermore, the ridge is not volcano-shaped, but rather elongate in an east-western direction. The aligned eastern and western borders of the

Truckee and Tahoe Basins define two parallel zones of structural ’weakness which have been the site of major 21 deformation, Pleistocene volcanic vents and very recent hot-spring and associated seismic•activity. It is inter- - esting to note that 7 of the 9 Pleistocene cinder cones in the area are in perfect north-south alignment along the eastern border of the trough formed by the two basins.

This suggests a linear zone of near-surface crustal weak­ ness along which future seismic and thermal events may occur. Following the orogeny, which post-dates the deposition of the Tertiary andesites, much of the topography and drainage patterns were similiar to that of the present. The Truckee River flowed north from the Lake Tahoe Basin, across the ridge separating the two basins (which acted to restrict flow), and into the Truckee Basin, The river eroded the Upper Truckee River Canyon to within 200 ft.

(61:m,) of its present level. It was onto this topography that the Pleistocene Lousetown Basalts were extruded. LOUSETOWN BASALTS AND LA.TITES The Louse-town Formation includes at least 20 different flows ranging in composition from hasalt to latite and sediments formed by aggradation brought about when the lavas ponded the drainage in the, Truckee Canyon.

This study deals with the geology and the engineering properties of the rock members in the Lousetown Formation and, therefore, will not treat the alluvial or gravel component. There has been little agreement as to the source of the flows. Lindgren( 1897) thought that they were extruded from numerous vents over topography .similiar to the present one. On the other hand, Hudson (1951) believed that the basalts were "...deposited in a continuous sheet on a surface of low relief..." (p. 941) and deformation followed resulting in the present topography. Taking into account Birkeland’s (1963) work in the area, Lindgren's intrepretation appears better.

Correlation and Age

The term "Lousetown" Formation was first applied by Thayer (1937) to a sequence of olivine basalts and pyroxene andesites of Pliocene-Pleistocene age which crop out in an area east of Lousetown Creek, about 6 mi (9 km north of Virginia City, Nevada. Thompson (1956) mapped other basalt flows near the Steamboat Springs area and 23 used the Lousetown nomenclature, Similiar Lousetovm flows were mapped in the Garson Range by Thompson and

White (1964). The correlation "between the flows in the

Truckee area to the Lousetown flows in the Carson and

Virginia Ranges is "based mainly on similiar stratigraphic position ana similiar rock type.However, recent radio- metric dating evidence has ‘shown that the type Lousetown

Basalt outcrop and the Truckee area basalt flows may be separated by as much as. 5.6 million years. Needless to say, there has been suggestion of renaming the Truckee area basalts to reflect this age difference (Bonham, 1969)*

For the sake of convience in this study, the Pleistocene basalt flows .in the Truckee area are considered part of the Lousetown Formation, and individual flow units within the formation will be termed members. Although the age of the Lousetown Formation in western Nevada is generally set at late Pliocene;; Heinrichs

(1967) dates it at 6.8 million years ago, the age of the Lousetown flows in the Truckee area (excluding the older Floriston Olivine Latite) is considerably younger.

Dairymple (1964) suggests a potassium-argon date of 1.2-

2.3 million years before the present. His chronology of the Lousetown Formation flows is shown in Fig. 5a. More­ over, the state of preservation of the flows and cinder

cones are suggestive of an early Pleistocene age. Flows have been notably eroded only along major drainage lines. 24

H ir s chd al e 01 iv in e L at it e s 1.3my

Bald Min. Olivine Latites 1.2ray

Big Chief Basalt

Tahoe City Olivine Latites 1.9my

Polaris Olivine Latites

Boca Ridge Plows

Alder Hill Basalts 2„3my

Dry Lake Flows

Florist on Olivine Latites 4. Gray

Fig„3A Sequence of Lousetown Formation flows in the Truckee Area, (from Lalrymple, 1964) Mineralogy

The olivine latite has two plagioelases present in the groundmass. One forms labradorite whose composition averages Ang.?, The other is a zoned plagiocl.ase averaging

An^g.. large phenocryst's are uncommon,. Euhedral to subhedral olivine occurs as pheno- crysts and less commonly, as part of the groundmass. Most olivine grains alter to iddingsite or celaaonite,

Augite is also common in the groundmass, their clear to M f l pale green color set them apart from the olivine. Common accessory minerals are magnetite and apatite.

The basa.lts tend to be glassy and thus, have no a n phenocrysts. Some of the vesicular portions of the flows have white crystals of anal cite!contained in the cavities.

Pillow lavas are associated with lavas that have flowed into water and glass is found where flows have cooled rapidly. Dissection of the flow surfaces has been slight and.

quite commonly, the vesicular upper portion of the flow unic is still well preserved. Cinder cones exhibit little dissection, but they do lack a summit crater. '

VOLCANIC ROCK CLASSIFICATION

In literature before 1962, the flows in the

Truckee area have all been described as basalts. Birlceland

(1963) has shown that both basalts and latites are present

His main arguement hinges on the fact that samples taken

from the Hirschdale Olivine Latite flow near Boca, Cali­

fornia have more than 52$ Si02 (Big. 4), the accepted hasalb-latite boundary as set by Williams, Turner and

Gilbert(1954). Rocks having greater than 52$ Si02 should not be considered in the basaltic category. As also shown in this figure, the flow at the type location of the

Lousetown Basalt Formation tends toward the all basalt average and is accurately termed a basalt flow.

Volcanic rocks bearing a resemblance to these basalts and latites, both in composition and in age, are reported to occur over wide areas in the Basin and Range province (Halva, 1961). Before they have been known as basalts; but recently, they have been noted as basaltic andesites or other more specific names. Fig. 4 Chemical Analysis of Lousetown Flows compared with Chemical Analysis of Basalt, Andesite and Latite

A B C D E Si02 49.1 54.2 54.0 53.5 51.8-51.9 O i—1 <3 CM K\ 15.7 17.2 17.2 16.6 16.8-18,8

Fe205 5.4 3.5 3 o 8 4.0 3.8-6.8

FeO 6.4 5.5 3.9 2.9 1.9-4.4

MgO 6.2 4.4 6.2 5.2 4.8-7.3

CaO 8.9 7.9 6.8 6.0 8.0-10.9 Na?0 3.1 3,7 3.3 4.4 2.8-3.4 k 2o 1.5 1.1 4.4 3.0 1.1-0.96

TiO? 1.4 1.3 1.2 1.6 0.96-1.0 p205 0.45 0,28 0.49 0.82 0.34-0.39 MnO 0.31 0.15 0.12 0.10 0. 17 h 2o 1.6 0.86 0.78 0.20 0.85-1.0

A- All basalt average (Daly , 1914) B~ Average andesite (Nockolds, 1954) C- Average latite (.Nockolds, 1954) D- Hirschdale Olivine Latite from Juniper Flats (Thompson and White, 1964) E- Two Lousetown Flows near type location, east of Lousetown Creek, Carson Range (Thompson and White, 1964) 28

LOU SET OWN FLOWS

In general, the chronology and flow extents of

the Lousetown Formation is difficult to determine because of several reasons, Flows are not usually in contact

with on. another and talus and/or glacial veneers obscure

The periphery of most flows, Despite these difficulties, Birkeland (1963) has satisfactorily deciphered the

chronology of the area. But there have been sections where, in the author* s opinion, he has not correctlv c delineated the flow. These readjustments are included in t the Geology and Geotechnical Map. z

09 Alder Hill Basalts ;1 The Alder Hill Basalts consist of one, possibly

two major flow units which outcrop near Alder Kill, north

of Iruckee, California. It is entirely underlain by

Tertiary andesite bedrock. The major flow (Alder Hill) Is up to 600 ft. ( 183m,) in places, The rock is medium-

gray to medium-dark gray in color, sometimes highly vesicular with white crystals of analcite present in the vesicles (Photo 4).

There is some disagreement here with previous investigations that have described two separate flow units in the low foothills northeast of Alder Hill. The author has neither found a flow contact nor any significant lithologic or petrologic differences. ■

>'%;i-.-;'«f4-;: -!H;-;‘v ?•

-;-,:**#;+* .'.jJvv-'- S « i i S ’:v ■ - .

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I ■•■ . - ,-.:;V. . /

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Photo Crystals of analcite in vesicles of Alder Kill Basalts The source of the Alder Hill Basalts is probably Alder

Hill itself. Bark reddish-brown scoria has been noted at

both Alder Hill and the cone between the latter and the town of Trucked. The unit is' bordered to the north, by

Alder Greek and to the -south by Bonner Creek.

This olivine basalt is probably the oldest flow

unit of the Lousetown Formation. Not only the potassium-

argon dates, but also its dissected nature and topographic position point to this conclusion. The flow outcrops

along approximately 5 mi (13 km ') of terrain.

Brv Lake and Boca Ridge-Flows

A distinctive sequence of approximately 9 flows

crop out around Dry Lake, 8 .km's, east of Truekee, Cali­

fornia in the southeastern corner of the Truekee Basin.

These flows range from hornblende basalts to olivine

latites to pure volcanic glass, and cover about 10 mi (26 krrr)...

There is a series of up to 5 separate lava flows

on Boca Ridge, west ox Floriston, California. Most of the units are fairly old but some are slightly dissected,

indieitive of young flows. Mineralogy varies greatly and the flows have a large vesicular component. About 2 mi (5 km" ) are covered by the flow.

Generally speaking, these 14 flows vary too greatly in age, mineralogy and physical properties to be considered useful for engineering properties classification.

Polaris Olivine Latite

A single olivine latite flow covering less than 0.4. 2 mi ' (1km) crops put north of the Truckee River about 2 mi

(3.2 km) east of Truckee, California. The flow lies on tuff

breccias and- is. less than 150 ft (46 m) at its greatest • •

thickness-(Photo 5).

There is some indication that below the latite

lies an old volcanic vent which produced the rather small

extent of this flow. But both the confirmation of a

Pleistocene vent and relative age of this flow are obscured by younger deposits of alluvium and glacial debris. Because of its limited extent, this latite flow is not sampled in

this study.

Big Chief Basalt

A distinctive Lousetown flow, the Big Chief Basalt

crops out along the east side of the Upper Truckee River

Canyon, south of Truckee, California. The flow occupies 2 2 3.5 rai'" (9 km ) in a flat-bottomed graben between the andesi

ridges of Big Chief and Sawtooth.

This flow differs from the other Lousetown flows in that it contains abundant glass, few phenocrysts and a rich, glassy, black color. Most of this flow is covered with a thin veneer of soil and is suspiciously devoid ox any type of flow? structure. Atop the soil cover lie a few's ?*'

:". : ' flMfigK^ * V . t-• • ♦*»•«» s ;#//•* vf '.•■•«

%.

Photo 5 Outcrop of Polaris Olivine Latite, 1-1/2 miles east of Truckee, California. Snow stake is approximately 15 ft. high.

% w & i y- -> : .

■■J«*5r V - --,V ,, v - . r .2-''. - 3$g

Photo 6 Mosses and lichens on Bald Mtn. Olivine Latite few boulders strewn about. They exhibit a characteristic grayish-red weathering "rind".

The source of the lava may have been surface fissures which delineate the NNE and SSW boundaries of

the pre-flow graben. Small amounts of scoria -were found ■ along the western fault zone. -

There seems to have been several drainage changes brought about by the-flow as evidenced by the present right angle bends in both Deer and Martis Creeks on the south and east sides of the flow,respectively.

Bald Mountain Olivine Latite

A single light brownish gray to medium gray olivine p p latite flow covering almost 7 ml" (18 km.), crops cut near :

Bald Mountain south of Truckee, California on the east side of the Truckee Canyon. It rests on andesite bedrock and is partially covered with glacial deposits and alluvium.

The contact between the latite and the andesite is clearly delineated by the pronounced break-in-slope between

& f200 and 6,400 ft. along the east slope of the Upper

Truckee River Canyon. Large talus slopes originating from the latite drape over the andesite and continue down the slope, grading from small to large, as it reaches the -

Truckee R, canyon bottom. There are only a few isolated patches of the olivine latite on the west side of the river, the thickest being only 75 ft (23 m) . East of the riv 34

the flow reaches up to 500 ft (152 m) thick. Most of the

olivine latite has an overall brownish-white coating where

it has been exposed to weathering.

Three cinder cones; Bald Mountain (elevation 6,760 ft), a cone at elevation 6,700 ft, and another at the 6,548

ft level, mark the sources of the Bald Mountain Latite. These scoria-marked cones which rise from 160-240 ft (49-73 m) above their "bases, still have the original symmetry, although erosion has somewhat destroyed their summit craters.

It seems evident that Martis Creek once flowed

northward into the Truckee River Canyon only to be diverted by the outflow of the Bald Mountain Olivine Latite. The *ia*« diverted river now follows a much longer and roundabout course via Martis Yalley. > ■Wwa Most rock slopes show no sign of chemical weathering

/though most of the olivine crystals are altered. Mosses and lichens blanket the rocks on the exposed bluffs (Photo 6).

Tahoe City Oily"ins Latite North and east of Tahoe City, California lies a flow which covers about 14 mi"" ("36 km') and consists of up to 800 ft (244 m) of olivine latite. The thickness accumulations occur at Thunder Cliff on the eastern wall of the Upper Truckee River Canyon about 2 mi (5.2 km) from the out-

let of Lake Tahoe . It is difficult to tell whether there is one continuous flow or many flows because talus extends

down to the river and obscures their possible contacts

(Photo 7). An age of 1.9 million years has been assigned to this flow by Dalrymp.le ( 1964),

Birkeland (1963) reports to have found pillow lavas at the base of the lowermost flow unit-, but never

higher. This would indicate flowage into water of the latite

Throughout the entire flow, a vesicular top section was not encountered. Whether it had been eroded away or

had never existed could not be determined. No noticeable columnar jointing was encountered.

Along the top of the flow, near the canyon edge,

the flow forms sheer vertical cliffs ranging from 10 ft.(3m)

on the western portion to 80 ft . (24m). at Thunder Cliff.

Spheroidal weathering is common along the talus slopes,

especially near the river; commonly exhibiting a reddish weathering stain (Photo 8)„

The first and only time the Truckee River comes

in contact with the Lousetown formation occurs about Imi (2. k m ) downstream from the Tahoe outlet. This represents a local "base level" for the river,and thus the lake;

because the basalt and latite flows are much more resis­

tant to erosion than the softer, more easily erodable.

andesite that otherwise lines the canyon. The river is

in the process of cutting through the flow which had at one time,darned up the river, considerably raising the level & '>V/<; ¥&J£*P& v «*£

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Photo 7 Talus slope of Tahoe City Olivine Laiite along Upper Truckee River Canyon. 2 miles north of Tahoe City, California, 37

Photo 8 feathering stain on Tahoe City Olivine latite

f f S I S I * 1 1 1 1

m m

, a&'iirfi&Sfl SWaW Photo 9 Columnar jointing, Hirschdale Olivine Latite 38

of Lake Tahoe.

Most of the Tahoe City Olivine Latite appear to have flowed from a vent marked "by a dissected cinder

cone near Bear Creek. Birkeland (1963) infers another vent on the south wall of the canyon. He postulates that the course of the Truckee River was most likely inherited

from the time when the lake drained through the low divide where lava from 'both vents met. Since, this time, the river has cut down almost 730 ft (222 m) in approximately 1.9 million years, or about 1 inch (2.54- cm) in 220 years.

r Hirsch.da.le Olivine- Latite (!*%»

A series of up to four very similiar flows cover fri‘Ur'mP a large area around Hirschdale, California, in the south­ ujj>vF: east Truckee Basin. The flow, dated as 1.3 million years '■m* o , o , old vhalrymple, 1964), covers better xhan 2 mi io.2 km“),

It is entirely atop Tertiary andesite, The flow was once a horizontal surface, very much like Juniper Elat, that had extended across the river to lap up against the andesites of Boca Hill. The Truckee River has since cut through the latite, leaving behind a very sinuous course which exposes a 200 ft (70 m) section of columnar jointing near the southwest boundary of the flow

(Photo 9). Juniper Flat is now mantled with nonmarine deposits of Pleistocene age. Two vertically different flows crop out on the 39

south hank of Juniper Creek, the contact being plainly

visible. Three mineralogically different areas were observed

on the northern section of the flow but no visual evidence

of a contact existed. Up to 480 ft (146 ra) of apparently

a single flow is seen 1-1/2 mi (2.4 km) north of Hirschdale,

opposite Boca Hill. Talus and scoria accumulations cover some of the lower flow and possible contacts are obscured. Vents which released the Hirschdale Olivine halites are marked by large amounts of cinder and scoria (Photos '

10-11). One cone, 165 ft (50 m) from its base,is located

at the west end of Juniper Plat and is presently being worked

by Sha-Neva, Inc., for cinders and scoria to be sold as light­

weight aggregrate (Photo 12-13). This marks the source of

the lava which flowed over Juniper Flat and the area to the

south and east, blocking the river.

Stratigraphic and structural evidence of Birkeland (1963) suggests that the flow is the youngest member of the Lousetown Formation rock units, even though Balrymple's

(1964) potassium-argon dates indicate that the Bald Moun­ tain Olivine Latite is 0.1 million years younger. Birkeland uses the presence of the Prosser Creek Alluvium (which formed when the Hirschdale flow blocked the river valley) atop the Bald Mountain Olivine Latite as evidence of the

older age of the latter member. 40

V

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/i&rr^sr*vV-^v ^ J ^ y '1%. r';-» :■ ; a r

v. *•?*.£< v-'-. ' V,.5 »'v - ^ F a :pS:i*.. M'.\VI1 6 i vi.w V. VU.K :.1 '!,-.-v :* j:v ■ '•■’• i ' ? :• ■ ■■- ' ■ ."■ / • ■ ^■ s, ■ ■■ e ■■■ ' '■■ V ; ■ - - < / .■ - .- v •>• *, . ■ - -\ - - -v; ' ' .-4 % ■ ■ ‘ ■:.v:-x : ''.:x'4 , • .'-s ' ' •*•:• _ ■ -• Photo 10 Scoria from source of Hirschdale Olivine Latite

42

Photo 12 Sha-Neva, Inc. workings near source vent of Hirschdale Olivine 'Latite

P n oto 3 light-weight aggregrate near source vent of Hirschdale Olivine Latite 4 3

Floriston Olivine Latites East of the town of Floriston, California lies

a brownish gray olivine latite flow covering just under

7 rni2 (18 kin2) , There has been no specific mention of this . flow in the literature, so it..will be -called the Floriston

Olivine Latite, It is extremely inaccessible; its base lies at the 6,800 ft, level on the east side of the Lower Truekee River Canyon. The southwestern boundary is extremely

faulted with the base of the flow being displaced as much

as 300 ft.(91 m). The flow is quite different than the other Louse- town flows in the Truekee area. It is moderately dissected, moderately to highly weathered in places (Photo 14) and totally weathered to clay (mostly montmorillonite) in depressed areas near the top ox the flow. This indicates that the flow is quite older than the 1.2-2.3 million years that is assigned to the Truekee area Lousetown flows. It also exhibits a conspicious platy parting,developed parallel to the flow banding, whose spacing ranges from

i/2 to 3/4 inch (1.27-1.91 cm). This platy nature plus the age difference would

seem to reflect a closer relation to the type Lousetown

Formation in the Virginia Range which carries a date of about 6.8 million years old, 44

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Photo 14 Highly weathered Floriston Olivine Latite exhibiting platy parting. 45

STRUCTURE AND FAULTING

The mar,or deformation in the Truckee area was

before the outflow of the lousetown flows arid formed the topography and drainage pattern onto which the Lousetown

Formation was deposited from 1.2-2,3 million years ago.

Deformation during .and after .this "Lousetown" period-was ...

somewhat less intense. Most faults- in the area are orientated in a NSW-

SSE direction which are sub-parallel to the major direction

of the late Cenosoic faults in the area, They are typical r. Basin and Range type, steeply-dipping normal faults.

SUMMARY OF TRUCKEE AREA EVEUTS

Lovejoy (1972) and Birkeland (1965) have summarised

-the major, events in the evolution-of the present-day

Truckee area: (1) Pliocene-Pleistocene formation of the Truckee

and Tahoe Basins (2) Pleistocene volcanism forming the Aider Hill

Basalts forcing the Truckee River south of Alder Hill (3) Upper Truckee River Canyon eruptions of the Tahoe City Olivine Latite and the Big Chief Basalt

which blocked the river and rose Lake Tahoe to the 7,000

ft. level (4) Bald Mountain Olivine Latit3 forced the Truckee

River into the present flow pattern 46

(5) Hirschdale Olivine latite was extruded blocking

Truc.kee River again (6) First glacial event occurs post-dating last

Lousetown 'member. 47

DESCRIPTI ON OF F10h STRUCTURE

At least 20 separate flows have been recognized i.n the Lousetown Formation of the Truckee area. They range from medium light gray to dark glassy black,, fine-grained latites and basalts.. For the most part, considering the wide range of petrology, the flow structures are surpris­ ingly s iidil i&r <. The general type of lava to be found in the Louse- town flows is a blocky type of lava with an "aa" top. Most of the flow is a blocky type because of the .regular- jointing which produces the smooth surfaces so character­ istic. of blocky lava. Aa lava is usually rough and frag­ mental. It is sometimes referred to as scoreaeeous, being very irregular in shape with jagged spines.

The basic structure of the flow units has been found to resemble the model of Swanson (1967) in which he based his observations on the Yakima Basalt in hasing- t o m In the Lousetown flows over 25 ft. (7.6 m) thick, zoning is apparent (Photos 15-17). As shown in Pig. 5, distinct columnar jointing occurs in about one-third of the total flow thickness in an area called the colonnade (Spry, 1962). Above the colonnade is an area of broken cross joints and massive blocky structure, including some pseudo-columns”. It is called the entablature (Tomkeieff,

1940 and Mackin, 1961). The entablature is glassier than the colonnade due to more rapid cooling. m p m P P M M m 0 W r Q ^ :

w | | rss^i -■ ■'

>..•. . -7 -/ ■ ■ JSgi ;\;w. , '■v r / v ..

i '

Pilot 0 16 Plow structure of Bald Mtn. Olivine latite 49

i

Vesicular lop jagged fragments -of granulated lava or glassy clinker similar to "aa" lava. Vesicles are elongated in direction of flow. Entablature™ massive blocks with prominent horizontal and vertical jointing, little flow structure, pseudo-columnar form Colonnade- vertical to slightly inclined columns, usually well-forme! when present Vesicular Base-glassy, vesicular zone; rubble or conglom­ erate -structure, occasional pillow lavas

Eiv. 5 Idealized Cross-section of Lousetown Formation Flows

51

The flow tops are vesicular, slightly undulatory to planar when bounded above by another flow (Photo 18), or irregular with pebbles and cobbles when the surfa'ce had

been exposed to weathering before being covered,.

The columns in the 'Colonnade area are somewhat

evenlv divided between the 5-sided variety and other (‘4- or

6-sided) varieties.

The entablature is very massive and jointed in many directions. Both the colonnade and the entablature

are coarser-grained than the top and basal structural areas ' pi'* because of the latter sections more rapid cooling rate

(Photo 19). | M Basal structures that are found in the Lousetown . HI flows include: (1) a pillow lava structure due, for the . - • . ~ ' most part, to flowage into water, (2) rubble-conglomerate

aone 1-10 inches (2.5-25 cm) thick, formed by incorporation of the pre-existing flow .surface into the new flow matrix and (3) a thick layer, about 1-3 ft (0.5-1 m) in thickness, made of glassy clinker or "slag" from the leading flow edge that was incorporated into the flow matrix. This "slag" had cascaded down from the partially solidifing lead edge of the flow in-a "caterpillar thread" (Waters-, 1960) fashion to be trapped underneath the flow as it advanced. This phenomenon has been noted and accurately described’with most lava flows of this type but as of yet, has not been found in outcrop (Waters, I960), hue to the relatively small thickness of the Lousetown flows,

r. -7

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Photo 19 Entablature of Bald Mtn, Olivine Latite 54

as compared to the Columbia Plateau Flood Basalts, more

basal structures could be found and observed. The author believes to have uncovered a "caterpillar thread" basal

structure in the Bald Mountain Olivine Latite, at tue

6 270 ft. level, east of the Truckee River, in Sec. 21 (Photo 20). The area is about 4 ft. (1.2 m) thick, contains

glassy "slag, inclusions" and' shows' strong evidence that this is a true "caterpillar thread" basal structure because

the glassy slag inclusions are surrounded by a much coarser-grained matrix. This slag might be explained as being

part of an already existing flow onto which the new flow

was extruded, if not for the fact that the base of the

’ Bald Mountain Olivine Latite is the Tertiary Andesite.

Most talus slopes are sourced from the outcrops

above by freeze-thaw action but seem to have fresh surfaces. Occasionally a boulder will exhibit spalling or exfoliation

and be reduced to a, spherical state mechani^alxi. Gct-mi,-a...

weathering was not found except for an occasional super­ ficial reddish-staining. Atop the older Floriston Olivine

Latite, chemical weathering has progressed much further,

reducing some low—reliei areas to clay. Parts of the flow, near the structural top and

nearest the source vents have .a vesicular nature, come

samples have a specific gravity of less than about 2.0

(125 lb/ft5) and are highly vesicular (Photo 21). Some

scoria at the vent itself may have specific weight of 55

•v t:

'■ ’ V V*.-’

•inn Kf: > ; ,^v£l :V-dl

■ - . fv

Photo 20 "Caterpillar Thread" type of Basal_ structure in Bald Mtn. Olivine Latite 56

59

*7 ^ less than 1 gm/cm-' (62.4 lb/ft ). The vesicules range from

1/16-1/2 inch (0.1-1.3 cm) with the average of 1/4 inch (0.6 cm). They are elliptical, evenly disperced, with the long axis parallel to the direction of flow. In the Alder Hill

Basalts, they axe filled with analcite. In general, as you approach the source vent, both the vesicular top and the basal sections become enlarged pr.o-' portional the total flow thickness. In the immediate vicin­ ity of the vent, no perceptible structure is apparent. It appeax-s as if the lava that had travelled furthest from the source had both the agitation and the time enough to rid itself of the dissolved gasses which is the cause of vesic- ularity. Even a distance from the vent, basaltic lava has an average viscosity of 10,000 poises (or some 100,000 times that of motor oil, Kittleman, (1979)). This will allow adequate flowage in all directions hampered only by elevation differences or partially solidified areas, Because of the ease of flowage of basaltic lava (the more acidic, latitic lava is slightly more viscious), vertical flow unit boundaries are very thin and hard to uncover. A few were found, how­ ever, showing a slightly vesicular nature acove ana below the contact. The contacts are planar with a slightly uhdula- tor y nature (Photo 22-23). It may exhibit signs of weathering on the lower surface. This feature can sometimes be followed throughout the entire flow and is roughly horizontal. 60

ROCK WEATHERING In general, throughout the Lousetown flows, the

effects of weathering are slight. This is mostly a function of the relative young age of the flows. Massive basic rocks .

such as basalt are first attacked both chemically and

mechanically, along joint planes, exfoliation flakes or

newly-formed freeze-thaw discontinuities; leading eventually

to spheroidal weathering (Photo 24). High proportions of

d a y or clay-sized particles complicate the weathering as

„ . f . this limits the flow of water through the rock disconti- '• ! i l l •nuities. Freeze-thaw along joints-has caused massive talus

slopes, partially stabilized by vegetation, to form along

the Upper Truckee River Canyon.

In a few selected places of the Hirschdale, Bald X I Mountain and Tahoe City Olivine Latites, small patches of

weathered bedrock occur.along joint planes, large areas of the same were encountered in the Floriston Olivine Latites.

Even though up to 70 inches (I.S.m) of soil occur in the Truckee area, most of the soil is of organic origin, and

is not • true rock weathering. Soils are light brown, sandy silt-clay, slightly

plastic averaging 40$ sand and the balance, clay-sized particles. The plasticity index averages 27$ and the liquid

limit 45$. The soil is classified as a CL—Oh soil in the Unified Soil Classification System. The major character­

istic is its strong acidity. The measured pH was o.2 at 61

tOsi’iv. '-tfr&'y W-K*&: i ■'■■■ i-Ui: i;fe;

l ‘ V.7, ■ ;■>■■■ ..y .7 -*s ! *yisv7 Photo 24 Spheroidal weathering on lower talus slones of Tahoe City Olivine Latites 62 the surface and 4.8 just above the slightly weathered bed­ rock. This acidity is characteristic of forest soils and of an environment in which montmorillon.ite has .formed.

Initially, as- niontinorillon.ite first forms, the environment is alkaline. Bui: the environment becomes progressively more acidic through imcomplete leaching of bases, reaching- a maximum at the point of conversion of montmorillonite to kaolinite (Fig. 6). One reaction which forms montmorillonite is the hydration of anorthite (which is common in the Lousetown

-flows) as follows: ANORTHITE MONT MORILL ONIT E ^'GaAlgSipOg+GHpO- 2H' 2(,A19(AlSi^) -jqO(OH) g) +30 a (OH) 2

Clays with slight: to moderate plasticity have a potential for swelling as the clay structure imbibes water. This clay has a moderate potential for swelling and a probable expansion of 5-10$ total volume change

(Chan,1975). This amount of swelling may create swelling pressures which can be potentially dangerous to foundation structures. Lying in elongated patches along the rim and parallel to the Upper Truckee River Canyon occurs a -soil that resembles a glacial till (.Sherwin to Tiogan in age) . This soil is a light brown, sandy silt with less than 4$ clay-size particles. This soil is classified as a CL; or an inorganic silt of low plasticity. This clay has a much

64 less percentage of clay and is therefore not considered to have a swelling potential.

An important engineering property of this type of glacial silt is its impervious, nature when compacted. This property can he put to use as a core for earth-fill dams or earth linings for canals. This'type of soil, however, which has a large component of silt, is very susceptible to frost-heave. It should be avoided as a subgrade material. SECTION III

Physical and Engineering- Properties of the Rock Unit 66

PHYSICAL AND ENGINEERING PROPERTIES OF THE ROCK UNITS

Introduction In order to accomplish the objectives of this study, rock samples were collected both horizontally and vertically throughout each of the five selected Lousetown members used in this study. Each flow was chosen by its importance as a member of the Lousetown Formation; usually with a rather large lateral extent exhibiting uniform rock properties.

All the samples were laboratory and/or field tested as outlined in Section IV. Sample locations are given on the Geology and Engineering Properties Map. Even though many studies have considered the engin­ eering and physical properties of basaltic rocksv none of them has dealt with the vertical variation in rock properties associated with vesicularity, In this study, both the vesicular portions of the flow and the massive colonnade entablature area were tested and compared. A new classifi­ cation system was also developed to predict certain engin­ eering properties of vesicular rocks. The physical and engineering properties reported in this study are intended to represent only average values for each geotechnical unit. They should not be used in lieu of a detailed site investigation program. As the data will indicate, the samples vary con­ siderably in their properties according to its vertical position within the flow. This position is related to the 67 vesicularity. For the most part, rock properties are

suprisingly uniform if collected along the same lateral

structural division. Most of the rock units display sparse soil devel­

opment, For this reason, soil properties are not discussed

in detail, .except where undesirable engineering behavior may occur. In order to provide a reasonable data base, an attempt was made to collect at least six specimens from each of the five flows where a substantial vesicular portion was present. Co ensure uniformity of description, the following terminology is used through this study: (1) joint spacing as set by Deere(1965)t (2) uniaxial compressive strength based on Deere and Miller (1966), (3) rock color description

conforms to 6. S, A. Rock Color Chart,,G. 3. A., ( 19/0; ,

(4) permeability descriptions by Dearman (1974), and (5) rock weathering classifications by Fookes, Dearman and

Franklin (1971). These are contained in Tables 1-4. Table 1 Joint- Spacing for Rock (after Deere, 1963)

Terminology Joint Spacing feet meters

very close <0.2 <0.06 close 0.2-V 0.06-0,3 moderately close 1-3 0.3-1 wide 3-10 1-3 very wide >10 - > 3

Table 2 Strength Classification for Rock ------(after Deere and Miller, 1966;

Ter minology TTni.axial Compressive Strength_lpst)

very high strength > 29,000 - high strength 14,500-29,000 medium strength 7,250-14,500 low strength 3,625-7,250 very low strength <3,625

Table 3 Permeability of Roclc Masse s (after Dearman, 1 ------— • - Permeabil it; Joint Description Terminology ft/sec m/ sec very close- Highly 3»0 — p 1.0- 9 Permeable 3x10 1x10"2 extremely close _9 1x10 J~ close- Moderately 3x10 2- Permeability 3x10 1x10". moderately close c: 1x10“q- wide- Slightly 3x10 Q- P erme ab ility 3x10 ^ 1x10"J very wide _Q -9 <1x10 3 solid, Effectively <3x'i0 un- ;j o int ed Impermeable Table 4 Rock Weathering Classification (after Fookes, Dearman and Franklin, 1971)

Terminology Grade Features

Fresh I Parent rock showing no discoloration, loss of strength or any other weathering effects.

Slightly weathered II "Rock may be slightly discolored near joints; rock material is not notice­ ably weaker than fresh rock.

Moderately weathered III Rock is discolored, rock material is noticeably weaker than fresh rock

Highly weathered IV Rock is discolored, original fabric of rock is altered. Corestones are present»

Completely weathered V Rock is discolored and changed to soil but original fabric of rock is mainly preserved.

Residual soil VI Rock is discolored and completely changed to a soil in which original rock fabric .is completely destroyed. There is large change in volume. 70

PREVIOUS WORK

In most books on rock properties, average basalt parameters are given as a guide usually encompassing a wide range range of values. However, in this study, a few parameters have been calculated that have no "baseline" values because they have never been calculated for basaltic rock. These include drillability, P-wave impedence and wave attenuation. These calculated parameters revealed a workable relationship with other rock properties. Previous literature dealing with compressive strength prediction include an equation developed by using multiple linear regression analysis. Nine rock properties from. 49 locations were investigated. by 1)’Andrea, Fisher and i'ogel- son (1965). The equations derived which have the highest coefficient of correlation have to be used with do variaoxes.

As less variables are included, the coefficients are reduced.

Prediction of compressive strength using sonic properties of sedimentary rocks was conducted by Avedissian and Wood (1972). Comparison of strengths of both dense and vesicular types of basalt has been conducted by button (1969). He shows compressive strength dropping off rapidly with decreasing specific gravity. This is. also shown to occur in this study. 71

USE AND IMPORTANCE OF ENGINEERING PROPERTIES

The unconfined compressive strength is probably the most commonly determined and useful engineering parameter because it is used to determine the rock’s bearing capacity for • foundation design considerations.- .Compressive strength alone is too simple a criterion to define the reaction of intact rock to external forces. A more thorough description of the rock sample includes the Elastic (or Young’s)

Modulus and Poisson’s Ratio which also consider axial and/or transverse strain when the load is applied. These two parameters provide the essential rock property data for studying the deformation of and the design for mine openings and mine structures (Mooney, 1974). They are also used to evaluate the deformations of a rock foundation under the loan of a structure, The Coefficient of Rigidity or Dynamic Shear Modulus (G) has particular importance for foundation studies and the response of .'structures to dynamic foundation excitation. Protection against earthquake damage requires information on shear wave velocity and Shear Modulus xn the underlying strata (Mooney, 1974). Shear wave velocities also provide vital data for stability analysis of ©atth dams, both old and new (Knill and Price, 19 72). Drillability can he used to calculate the raoe of tunnel advance, fox engineering cost estimation. Seismic velocity and overall rock quality, RQD, have been usefully correlated to the *7 O rate of tunnel construction and set spacing for large tunnel construction projects {Scotty lee, G.,troll and

Robinson, 1967). Seismic wave velocities can indicate whether a formation can be rippable, or excavated with a D9 tractor.

A useful relationship exists between seismic velocity and grout take in dam cutoffs and zones of consolidation grouting

(Knill and Price, 1972). In general, engineering properties of rocks are very useful in evaluation of engineering design criteria, although, the state of the art in these correlations is still in its infancy. 7 3

PHYSICAL AND ENGINEERING PROPERTIES OP THE l 0Tj3 ^ q^ - BASAL.j S AND "LAIITES

Alder Hill Basalts The basalt flows near Alder Hill are the oldest member of the Truekee area Lousetown flows. This flow is one of the two major members that is studied both hor­ izontally and vertically. The vesicular portions of the flow, in some places, comprise over half of the total flow thickness, averaging about 1/3. The larger percentages occur near the source vent where minor amounts of scoria are found (the scoria is localised and was not sampled,;. Even though the vesicular top has porosities of from 18.6-25.’596, the rock mass is slightly permeable because the voids are not interconnected and most permeability is a function of the joint spacing. The housing developments that have recently been built on the southeast side of Alder Hill have been, limited to areas in which the soil cover is at least 3 ft. (1 m).

Thev are relying on the vesicular basalt, which lias a tendency to have more jointing than the massive counterpart, to furnish at least a slightly permeable rock mass which is needed for adequate septic tank use. Although, in some cases, this waste water; whether fully treated or not, has seen noted trickling out through horizontal flow boundaries just below the point where the water had been introduced.

Jointing is generally moderately close to close 74 with soil covering most of the flow surface in thin layers which support a moderate growth oi trees. Soil cove^ thins

out to only a few inches near the top of Alder Hill where

housing developments have not "been constructed to date.

Minor amounts of potentially swelling clay, found

on the entire south side of Alder Hill, have added to the

problem of inadequate permeability .in the rock unit. 2he

clay has clogged up some of the smaller joints and has inhibited waste water percolation through the rock mass.

Most of the clay is in very thin seams,so tne residential

foundations and the roads are not founded on large amounts

of this type of clay, but rather on the basalt itself. Compressive strengths for tne vesicular basalus

are from 3,580-7,440 psi (average of 5,410 pai or low-

strength category). This is really not as strong as the term ’'basalt" suggests. This in the relative strength range

of some weakly-cemented sandstones and shales. If large

structures are built on the top section of the member, localised pressures under some footings may no •. ha ire a

completely desirable factor of safety. Compressive strengths for the massive hasalxs range

from 19,500-21,750 psi (averaging 20,320 psi or high strength classification). As expected, the higher compress­

ive strength massive rock also has a higher Elastic Modulus,

unit weight and sonic wave velocity, but lower porosity,

than the vssxcular samp!es. 75

The slopes of Alder Hill appear to he stable, but because of their steepness, lack of vegetation in some places and little soil cover, there may be areas of rapid soil erosion where local rock or mud flows may occur. Overall, this rock unit is slightly-moderately weathered. Rounded, boulders of oasalt are common neai the? top of Alder Hill. They exhibit a rusty staining about 1/4 _ 1/2 inch (0.6-1.3 m) thick around.the outside.

Big Chief Basalt This flow is characterized by abundant glass, very few phenocrysts and a rich black color. Only a small percentage of the flow crops out and.this only occurs along

Mart is Creek,which marks the eastern boundary of the flow.

The outcrop shows a massive flow, devoid of any type of structure, with no vesicular component. Along the western perimeter, there is some indication of an older .clow under­ lying -the Big Chief Basalt that had once occupied the graben- valley. This older flow is in a line parallel to the con­ tact of the Big Chief Basalt and the andesite of Little Chief Mountain. It is slightly weathered, exhibits a platy parting and is an olivine lari',e. Compressive strengths of the Big Chief Basalt range from 29,500-34,200 psi (averaging 31,320 psi or in the very high strength category). This strength is very typical for a massive basalt that contains no defects. 76

Joint spacing is wide and fairly continuous. There are primarily two vertical joint sets at approximately right angles to each other. Because of the flow structure which causes widely spaced horizontal jointing, the flow has a very bioeky appearance. The flow occupies a valley and soil cover ranges

from a few inches up to two ft (5 cm to 0.6 m). The soil is a pebbly silt of organic origin, feathering is slight with rounded boulders peeking out through the soil cover. Iron-staining in the boulders is the rule, with no indi­

cation of any strength loss. Even though the flow is very

basic in composition, pockets oi clay were not uncovered.

This may be due to the extreme hardness and competency of the flow or its protective soil cover.

Bald Mountain Olivine^atite

This olivine latite flow is one of the largest

single flows in the Lousetown Formation. It has 3 visible

cinder cones encircled by a ring of reddish scoria. The western boundary of the flow is along the

Truckee River and is marked by 80-100 ft (24-30 m) of vertical cliffs and partially vegetated talus slopes that

reach down to the Truckee River. This is the second of the two flows that was

studied both horizontally and vertically. The vesicular,

light brownish gray top ranges from 5-100$ of the total flow

thickness with an average value of about 1/iO. Ine compres- 77

ive strength ranges from 5,00-8,580 psi (averaging 6,590 psi or low strength). Correspondingly, densities are low

and porosities are high; ranging from 2.51-2.32 and 16#3-17.2$>, respectively. As with the Alder Hill Basalts,

this high porosity does not indicate a high permeability. The void spaces are not interconnected and the rock mass

permeability is slight. The massive medium gray entablature and colonnade

sections have a much higher compressive strength. It ranges

from 12,600-24,180 psi (averaging 19,190 psi or high

strength). This range is rather wide but one of the

samples had many planar flow structures and fractures

which weakened the sample in compression causing the very

low value. The extreme northern boundary of the flow is a

bluff overlooking Truckee, California. This area is now

being saturated with modern housing developments. It is covered with soil to an average depth of 3 * 5 ft, (1 m) . This,

plus the Slight permeability of the rock mass, is causing

problems, to the people who live atop the bluff. A portion

of the leach field water is running out through tne joints

onto the cliff face ^usfc below their houses. This adas

to the freeze—thaw, not to mention tne sanitary and

aesthetic problem. As was mentioned in the section dealing with

rock weathering,pockets of potentially swelling clay aa^ 78 glacial silts that are susceptible to frost-heave, were found along the western and northern boundaries of the flow. These should be avoided in engineering projects.

Most jointing is widely spaced showing one random joint orientation and three vertical joint sets, The one random orientation is paralleling the river and is more prominent that the joint sets. It is probably due to expansion upon unloading when the l'ruckee River cut its canyon,relieving some horizontal stresses. There is also a very widely spaced horizontal jointing which produces the blocky "appearance along the western boundary (Pnoto 25).

Below the western cliffs are large talus slopes which grade from large to small boulders from the river,upslope. Some vegetation occurs at the upper portion. The smaller boulders near the cliff bases are very near the angle of repose for the material. This may cause instability during seismic loading. The lower talus rests on a gentler andesite-• slope and appears to be stable.

Although free z e-thaw action has piled up an extensive talus, the boulders are essentially unweathered chemically. Some exhibit some mechanical weathering in the form of exfoliation slaos (1.27~1.9 cm) l/2~3/4 incn thick Lichens and mosses cover many of the north—facing ro ck i ac

80

Tahoe City Olivine latites

The thickest accumulation of a member of the

Lousetown Formation occurs just north of Tahoe City, Cal­ ifornia. 800 ft. (245 ml) have been noted and talus coverings ma

(1968), a seismic refraction study indicated a zone of "higher velocity rock" underlying the surface olivine latite, although certainly not deep enough to be the basal andesite*

This can be another latite or basalt flow older than the

Tahoe City Olivine Latite or just the latter that is less fractured and jointed at depth. Most evidence, including a borehole TV camera used by the California Dept, of water

Resources, points toward there being just one single Dio.'.' of latite. A prominent vesicular portion was not found m this

flow, but 3-4 in (9 cm) of somewhat vesicular rock capped

the flow in places. There is no way of telling whether this is the approximate original flow top or an erosional

surface. Compressive strength of the massive latite ranges

from 21,460-21,750 psi with only two samples tested, m i s

high strength category rock has a specific gravity m 2,77. The total flow has very uniform properties for a flow

of such a large lateral and vertical extent. 81

The western boundary of the flow, which is along

the Upper Truckee River Canyon, is very similiar to the Bald Mountain Olivine Latite. Massive talus slopes exist here also, hut are derived from a much smaller cliff source. Freeze-thaw action in not as much a factor in

slope instability as the larger cliff faces further down

the river. This flow has few examples of true columnar

jointing; though rudimentary columnar jointing appears

at the base of the cliff face. There is one major vertical

joint set, the orientation paralleling the river is more continuous and prominent than its orthogonal partner. They

both dip slightly from vertical to the Yt—SW» Joint spacing is wide in both horizontal and vertical oxients.oi.ons and

is not very well developed. Soil development atop the flow has progressed

enough to form 80 in (200 cm ) of organic soil in places.

The soil seems to be very acidic and slightly plastic near

the bedrock area, potentially swelling rnontmorillonire­

type clays may exist. The cliff face is completely devoid of chemical

weathering except for moss and lichen coverings. Freeze-

thaw action and exfoliation are active in producing the

rather large slopes. But only a few boulders have a pale

reddish brown staining on the outside few millimeters.

This disparitv in weathering evidence may be due to two 82 reasons: (1) the mechanism that produces the staining may take more time to manifest itself than the process of exfoliation. In other words, exfoliation may interrupt the staining process, not allowing large, intact boulders to become stained, or (2) staining rates may be due to minute differences in the chemical composition of the rocks.

The source of the Tahoe City Olivine Latite is a rather large cinder and scoria plug atop the Pleistocene vent at the 7,600 ft. level near Bear Creek. The scoria covers almost 0.4 mi (1 km ) and is up to 125 ft. (38 m.) thick (Matthews and Franks, 1971). This cinder cone was used as a waste water disposal site beginning on April, 1970 for the northwest shore communities of the Lake Tahoe Basin. Because of the great thickness of the predominantly vertically jointed latite and its highly permeable:scoria area, the waste disposal site was able to handle up to 2,94 million gallons per day (1.11x10^ nr per day) (Riadel, personal communication). The site consists of 44 acres (1.78x10^ m“) with 15,000 ft. (4-570 ra) of trenches. Most of the water flows through more than 800 ft. (245 m) vertically (the actual distance may be 1.5 times that distance) and exits through a spring, even­ tually finding its way out of the basin by way of the Trueke

River. The spring is monitored for environmental impact and levels of chlorides, conform, COB and BO seem to he ac­ ceptable (Franks, 1970). Now, this cinder cone is inoperable con ’7

Treatment was stopped in 1977. North shore communities are now connected to the Truckee Waste Water Treatment plant via a pipeline that runs along the Upper iruckee

River Canyon.

Hirschdale Olivine Latites

The Hirschdale Olivine Latite is the youngest rock member of the Lousetown Formation. It also has the most well developed columnar jointing and the most extensive scoria-cinder vent area. It is interesting to note that no correlation exists among the members between the age of the flow, amount of columnar jointing or amount of scoria present, A sizable amount of a vesicular top was not encoun­ tered throughout the flow, although it very well may exist.

Most of the flat top of the flow is obscured by a mantle

of scoria, soil cover and Pleistocene deposits. Most of the information about the flow was obtained from outcrops along the Truckee River, Juniper Creek and from observations

near the source vent. Compressive strength is the largest obtained

throughput all the sample testing. Strength ranges from

32,180-39,200 psi. The 35,190 psi average is well into the very high strength region. Indicative of this high strength

are the very high values for Elastic Modulus, sonic wave

velocity and specific gravity with a corresponding Ioa- porosities. 2 2 The cinder-scoria covers about 0.6 mi (1.5 km') and is at least 250 ft (76 m) thick at the vent center.

The scoria and cinders are being mined as a local source of light-weight aggregrate. Specific gravity ranges from

0.7-1.3 and has an angle of repose of 39°. Sices range from 3/4 to 2-1/2 inches (1.9-6.4 cm). Colors are light brown to brownish red. On the southwest flow boundary, adjacent to the river is an excellent example of columnar joinring. The

base of the flow is obscured by talus, out the coiorniade, entablature and the vesicular top are readily apparent. The columns are mostly 5-sided (about half have five sides, the

remainder is split between 4 and o—sided columno). ihey are approximately 2- 1/2 to 4 ft (0 .8- 1.2 m) in diameter.

The entablature has a few curved columns with a much smaller

diameter. Most of the entablature is a rather blocky type of

rock exhibiting widely spaced joints. This.area is much moie

susceptible to freeze-thaw action and usually exhibits a

break-in-slope at the contact between the two structural

sect ions The columnar section was exhumed by the Truckee

River by erosive action against the southwestern flow boundary. The author assumes that most of the Hirschdaxe Olivine Latite, below the surface, also exhibits this same colonnade-entablature structure. The following 85 explanations will be advanced as to why some flows display columnar jointing and others (even in the same flow unit) do not: (1) the flows may be too thin to have the necessary

slow cooling rate to form columnar jointing, (2) the isothermal gradient had changed at one point (groundwater?) not allowing uniform growth perpendicular to the isothermal lines, or (3) the lava was too gassy and could not build up adequate tensile stress to form cooling joints.

The boundary slopes of the flow member are fairly

stable overall, although in a few areas, rock falls nave

occured. The scoria ta3.us is resting near the angle of repose of the material and may be unstable upon further river downcutting.

Just as the Tahoe City Olivine Latite, the cinder

cone area is extremely permeable. Weathering throughout the flow is insignificant except for the ever present freeze-thaw action. Exfoliation is rarely evident. Soil cover is of organic origin and potentially swelling clays

are not expected to he present. 86

SECTION IV PHYSICAL AND ENGINEERING PROPER!IS3 DETERMINATION 87

UNIAXIAL COMPRESSIVE STRENGTH The uniaxial compressive, or crushing, strength is probably the most common and useful strength property that can be determined from a rock sample. Ey definition, the compressive strength is the stress required to crush a usually cylindrical sample which has no lateral confinement.

Although the use of a relatively small specimen tends to ignore the effects of rock mass faulting, jointing, bedding and other rock defects; as a rock mass approaches homoge­ neity, with widely spaced joints as in the Lousetown members the compressive strength provides sufficient information for design purposes. True compressive failure m a rock can only .u- through internal collapse of the xotal rock strueuuc. j.h.j.o usually occurs by compression of the rock pore spaces, inducing grain fracture (mostly occuring in sedimentary rocks) or by movement along grain boundaries (igneous xoox,= )

But since time compressive failure requires hydrostatic loading (no tension present), the compressive strength of a rock specimen is, in many ways, a reflection ox res shear

strength. This is the stress at which an unconfined rock

fails in shear. Since a cylinder of rock in a crushing test

would fail, prematurely in shear; the compressive strength

might be more accurately described as the shear failure

level under uniaxial stress (Banner, 1968). Uniaxial compressive strength is affected oy many 88 variables; among them are the following: test procedures, end-contact conditions, end-restraint conditions, specimen size, specimen proportions, pore fluids, porosity, duration and rate of loading. Rocks are much stronger in compression than in tension, The relationship is:

v kst where: is compressive strength

S+ is tensile strength

k varies between 4 and 10 depending on the rock type

In most uniaxial compression tests the rock specimen fails on conical shear surfaces that have bases at tne restraining platens. Along these conical surfaces, the shear failure occurs, showing considerable powdering, crush­ ing and abrasion (Photo 26). with very glassy, homogeneous samples, a distinct failure plane usually forms, along which all shear occurs (Photo 27). Maximum shear stress occurs when the failure plane is at 45 as snovn by cne formula:

T = 1/2 (OTsin 2 0) where: T-shear stress . „ . n C{ =eonroressive stress of rock ax failure © = 90-failure angle,**. (see Pig. 7)

91

LOAD

4

LOAD

CT=Normal Stress -Shear Stress oc --F ailur e Angl e

Pig,7 Shear and Normal Stresses Acting on Failure Plane at Failure Angle 92

Rocks with high to very high compressive strengths, mostly fine-grained igneous rocks, metamorphic rocks and massive limestones and dolomites fail very suddenly, with

a slight explosion, if a "stiff" test is used, failure usually occurs at extremely low strain levels. Axial strains range from 0.002-0.005 . Lower strength rocks, sedimentary

and weathered igneous rocks, along with vesicular rocks, generally fail less suddenly and very uneventfully. Yielding

often occurs prior to failure. An in depth discussion of rock strength and failure mechanisms may be found in Obert and Duvall. (1967). UNIAXIAL COMPRESSIVE STRENGTH TESTING

The uniaxial compressive strength testing was performed according to the ASTM (1971) Standard Testing

Method. For this study, a larger than standard diamond drill hit was used to obtain a more representative root sample. The inside diameter of the bit was 2-1/8 inches (5.4 cm); NX core size. The sample length was 4-1/4 inches

(10.8 cm) giving the required length to diameter ratio of

2:1. Empirical equations have been derived (ASTM, 1971) to correct apparent compressive strengths to the standard 2:1, length to diameter ratio. Compressive strength is:

P 8. T

where: S is compressive strength 0 p is applied load A is cross sectional area of specimen

Natural variations in rock strength among samples

often result from weathering, microcracks, flow laminations

or other rock defects. In very homogeneous rock masses, fewer rock samples are required for reliable testing result

Testing apparatus is shown in Photos 28-29.

Testing results are given in TaDle 5. U ^ f S h M

- #S Us;W S s S 0 e $ m ; ’U'^'j' ■ - ■ U" .t/ SS&&9I IfiSkft :■ Iferril? m W m j

lisliSfia .

. . i* : W m m m m ip® IpsSjSSiSSS

Photo 28 Compressive strength testing apparatus mmt-

• 'll IftfiK :■;./ :_ ■ M«$! I ;: 1'.

- HHUHfesM»Ki Photo 29 Sample of Bald Mtn. Olivine Latite in loading device after compressive test FRANKLIN POINT LOAD STRENGTH Franklin, Brock and Walton (1971) have described a field test that is comprised of a small ram mounted on a loading frame (Photo 30). In recent years, the point load strength has gained wide acceptance as a field method to indirectly determine the tensile strength of anj brittle material. This can be related directly to the compressive strength in the case of rock. This wide acceptance has grown for the following reasons: (1) little or no sample preparation is needed, (2) the loading apparatus is rela­ tively inexpensive, simple to operate and can be used in the field, (3) irregular specimens can be tested, and (4) the test has a high degree of reproducibility. When the load is applied to the sample, a hign stress concentration occurs at the center ox the specimen.

This leads to the development of tensile cracks parallel to the applied loading. Since this crack begins ax the center of the sample and propagates toward the outside, minor imperfections on the outside of the sample have little effect on the test results. In vesicular rocks, the Point Load Strength Test has been shown to give erroneously low compressive strengths because of the interference of internal and surface vesicles

For this reason, the Schmidt Hammer, as combined with cor­

rection factors for porosity and specific gravity, has 9

"been used in this study with better results in predicting compressive strength. 98

PVs«si*L';-- •'. -v*V

M *fg W ' ' <;.- vfr®-:w»J

■w m aS&wi

2* <■ ••■'" ! jj|: jjt t

Photo 30 Franklin Poin'c Load Testing Apparatus 99

FRANKLIN POINT LOAD STRENGTH TESTING

For this study, all specimens were tested "by using

the irregular lump test method which requires no sample preparation, such as coring. This most closely follows the

ideal of "pure field" testing. Lumps are approximately two inches circular and placed in the apparatus "between the platens. Point Load Strength Index, Ig, is calculated

as:

P

where: P=Failure load D= Platen separation Corrections were used to correct the Ig value to

a standard reference diameter of 50mm. These values are

then plotted against the compressive strength and an equation

is derived to convert "the strength.

fp-L a st results are given in Table 6. 100

APPARENT SPECIFIC GRAVITY- APPARENT AND TRUE POROSITY

Apparent specific gravity is defined as the ratio of the weight of a specimen of a given exterior volume to the weight of water that would fill that volume. This does not take into account the void spaces, so the true spe­ cific gravity of the solids in the rock can only he equal to or greater than the apparent specific gravity. This property is useful in determining overburden pressure at depth. The apparent specific gravity is given by: Vi ASG— ^ d a e w where: ASG is the apparent specific gravity V/ = dry unit weight of rock V = exterior volume of rock e $ = unit weight of water W = saturated weight of rock

Apparent porosity is defined as the ratio of the

open pore space to the exterior volume of the sample. In very porous basalts and 'latites, vesicul.es or cracks may

not be interconnected, This makes it almost impossible

to completely saturate the sample. So, true porosity can only be equal to or greater than the apparent porosity

Apparent porosity is; VV -V* j s d AP= X 1OOJt 101 where: AP is the apparent porosity ,nd tfv; as defined above. V‘r; rld, »,’ V v e„ ci ror very oorous samples in this study, true porosity was calculated by comparing the specific gravity of ground­ up rock to the exterior volume. Small changes in porosity can have drastic changes

in compressive strength. Internal cohesion in rock will

obviously he affected by the amount of internal contact

between the grains. Decreases in compressive strength of up to 55i° due to saturation have been reported. Studies involving static elastic constants have shown decreases

of up to 40io when samples were tested in the saturated

rather than dry state (Farmer, i960). Test results are given in ‘table. 5. 102

SCHMIDT HAMMER TEST

Ths Schmidt Hammer was developed in 1948 by Ernst

Schmidt of Switzerland. It was initially used to estimate the strength of concrete. It has recently been used by researchers to estimate the compressive strength and the

Elastic Modulus of rocks. It is designed on the principle that a spring-loaded hammer„ with a given amount of eneigy, will rebound some distance when impacted against a solid mass. The amount of this rebound is measured and directly related to the competency (or strength) of a rocK. The

Schmidt Hammer has gained favor in recent years because of its reproducibility and extreme portability (Photo 31).

To arrive at the Schmidt Rebound Value (S'RV) . 25 readings are taken on a rock outcrop. The lower 12 values are then discarded as being invalid due to testing tech­ nique. The median-of the remaining 13 values is .the ;Scnraidt

Rebound. Value.. The Schmidt Rebound Value has been related to the

compressive strength and the Elastic Modulus by both Deere

and ■Aufrauth via the use ,of the dry unit weight. Aufmuth's

values range from 1.3-2,2 times greater than Deere's values

Deere's method usually comes closest to estimating the

actual compressive strength of a rock. For this reason, Deere's method was used for this study. Correction factors are available for non-horizontal impacts. Many factors have an effect on the determination W : 'y:i

Photo 31 Schmidt Rehound Hammer 104 of the Schmidt Rebound Value. If the sample is rough, saturated with water, interspersed with foreign rock frag­ ments, inhomogeneous or full of microcracks or fractures; the rebound value will be erroneous. The single most important factor is the soundness of the tested area.

Por best results, the tested area should be very firm and not be loosely attached to the rock mass. Samples tested in this study were fs-irly free of the above imperfections.

When vesicular samples are tested, they give deflated values for the compressive strength. This is because the rebound value is only a measure of the hardness or the competency of the rock material and does not take into account any of the rock defects, sucn as vesicle^, .these defects tend to lessen the compressive strength. Graphs using the Schmidt Rebound Value and taking into account the porosity and specific gravity of a rock sample are derived in this study as the most accurate means of pre­ dicting the compressive strength of vesicular roc/.s.

Test results are given in Table 7• ULTRASONIC VfAYE TESTING

Determination of dynamic elastic constants (E^, ji , Gd and K^)can be made by calculations involving the compressional, or P-wave velocity, the shear, or S~wave velocity and the specific gravity of the specimen. Sonic wave velocities were determined (both P and

S-wave).. for each sample according to the ASTM ( 1969) Stan­ dard Testing Method. The apparatus used is shown in a generalized schematic in Fig. 8..As shown in the diagram, a. pulse wave generator simultaneously delivers a short duration electrical pulse (either compressional or shear) to the dual beam oscilloscope and also to drive the piezo­ electric crystals. A reference ’’tick" is seen on the oscil­ loscope which shows that the system is working. Upon receiving the electric pulse, the piezoelectric crystals begin to vibrate in a longitudinal or transverse moae, decending on the hook-up. This vibratory motion is trans­ mitted through the rock specimen and reconverted to an electric pulse by the receiving crystal. The pulse, atten­ uated by frictional and energy losses within the rock specimen, is displayed in a wave form on the oscilloscope (Photo 32). The testing apparatus is pictured in Photo 33. From the oscilloscope display, two parameters can b e d e t o rm in e d: (1) the pulse wave velocity (both P and 3-wave) by: I

S l f t S ®

i S i Bh K agSaiSK' Iffigp .; : M B ff V

cm vcmtoj-cv 'vi-ftitiiMi y -' iwjAfrfAiJ** *~, ~ P 7 8 a s t & IK*

! .. i s i t i = i

Photo 32 p 'wave (above) and S wave (below) traces on oscilloscope. 107

G3SB2SZmm &

§0&

w § M m M W m m W s -4y *s photo 33 Ultrasonic Pulse Wave testing apparatus 1 Pulse Generalor~H,P. Model 3312A 2 0scilloscope-Tektronix 5103 N (D13) A Dual-Trace' Amplifier Model 5A18N 33 Differential Amplifier Model 5A21N C Dual Time Base Model 5B12N 3 Piezoelectric Crystal Housings-SBEL Model P&S Range 1*0 MEG

Fig. 8 Schematic of Pulse Wave Testing Apparatus 109

Y = --- -— piil.se t and (2) the wave attenuation or transmission efficiency,B of the specimen by; y B= out x 100?j v in where: V , is the pulse wave velocity pulse x L = the length of the specimen t- the time required for wave travel through the rock, B= the wave attenuation of the rock V out ,=the voltageo recorded at the receivingu crystal V^n= the voltage recorded at the transmitting crystal

Krishnamurthy and Balakrishna (1957) have determined attenuation characteristics for several rocks. Attenuation was seen to inci’ease with frequency of the wave in fine­ grained rocks, but with larger -grain-size rocks (dolerites, limestones and marbles), attenuation was independent of frequency. Attewell and Brentnail (1964) have adduced that attenuation is due to scattering of wave energy at grain and pore b oundar i e s. Test results are given in Table 5. 110

ELASTIC CONST MT S

For many design purposes, rock is considered to be an elastic medium. Elastic media show instant and total recovery upon removal of stress. This is the fundamental basis of the elastic theory (Timoshenko and Goodier, 1951).

At lower stress-strain levels, rock tends toward this ideal. Elasticity of rocks depend on 3 major factors: (1) isotropy or directional orientation of minerals or rock grains, (2) homogeneity or physicalocontinuity of a rock, and (3) continuity or number of microcracks and pore space in a rock. The most elastic rocks will be fine-grained, mas- sive and compact rocks such as extrusive and plutonic igneous rocks. Less elastic rocks are coarser-grained igneous rocks and fine-grained compacted sediments. Non-elastic rocks include less cohesive rocks with large pore space. For the latter case, an assumption of elasticity for design v/oulc. be dangerous. Several elastic constants are used to define the degree of elasticity of a medium. The Modulus of Elasticity or Young's Modulus is the most useful and commonly calculated cf the elastic constants. It is defined as the ratio of stress aplied to the corresponding axial strain. This value is usually determined from the average slope of the linear portion of the stress—strain curve.

The Modulus of Elasticity is defined as: where: AG'= the change in applied stress axial strain E= Modulus of Elasticity

The greater the E value, the less will be the deformation produced by a given value ox applied stress. For inelastic materials such as less cohesive rocks

and some plastics, the Modulus of Deformation more ade­

quately describes the "state of elasticity", although

both describe the "stiffness" of a material. The change of shape of an elastic material subjected to a shearing force is determined by its Modulus of

Rigidity of Shear Modulus, G. It is defined as (Fig. 9):

r shear stress '“shear strain An elastic material subjected to a uniform pressure from all directions would experience a hydrostatic compress sive stress. Its volume would be effected by any change in the applied pressure. The Bulk Modulus,or Compressibility, K, of the material measures the extent of that change. K is defined as:

change irg pressure K= original volume x change in volume

then a load is applied to a material, not only does axial strain occur, but also transverse strain results (Fig,

9), Poisson’s Ratio, p., is defined as the ratio of the LOAD

Final Shape

(A)

LOAD — -- —-fr*

r -Axial Strain '-'a 0 .^Transverse Strain o =Shear Strain (©in radians)

Fig. 9 Loading Induced Strain A. Axial and Transverse B. Shear 11 transverse strain to the axial strain as shown:

where: £ .^transverse strain axial strain

From an idealized crystal lattice structure for a perfectly elastic material, it can he shown by geometry, that Poisson’s Ratio equals 0.333 (Farmer, 1968)„ Stress levels used to calculate Poisson’s Ratio should be less than one half of the failure stress of the rock. Poisson's

Ratio for this study was calculated for a stress of 7,153 psi The three elastic moduli are inter-related as shown 114

DYNAMIC ELASTIC COIN ST AM’S DETERMINATION

Determination of dynamic elastic constants (E^, and ) can be made by calculations involving the P wave velocity, 3 wave velocity atid the specific gravity of the

sample. The equation for the Modulus of Elasticity, E^ is: v/tf 3(V / V J 2 -4 •p _ <->____ _p s q ___ Ld- g IVp7vs)2 -1

Poisson's Ratio is determined by:

(Vv X)'/V s')2 “2 p = 1/2 — ? (v./vj.U - o -1

The Modulus of Rigidity, G^, is: Ea Ga=- = - 4 - V 2 6 S

The Bulk Modulus, , can be calculated by: V JJd

3( 1“ 2p.)

where: V = the shear wave velocity s V = the compressional wave velocity 5a - the unit weight of the specimen g= the acceleration due to gravity equations are taken from Obert and Duvall, 1967.

Rocks can usually resist a higher magnitude of dynamic load that of static load. Comparative values from 115

Rinehart (1962) show that in all cases the dynamic strength is from 5-10 times the static strength for the same rock; probably nearer 5 for stronger rocks and 10 for weaker rocks. Avedissian and Wood (1972) have shown ratios of dynamic moduli to static moduli of 1,1-1.93.

The reason for the large increase in strength and elastic constants under dynamic loading condition must lie in the transient nature of the stress pulse and its local­ ized area of stress. Failure mechanisms in the rock which are also time- dependent are incapable of completion during the pulse duration.(Farmer„ 1968). A study by Avedissian and Wood (1972) dealy with the difference between dynamic and static determinations of the Modulus of Elasticity. They empirically related the two parameters by this equation:

E = 0.595 Ed + 0.209 x 106 psi

where: is the Dynamic Modulus of Elasticity E is the Static Modulus of Elasticity o This relationship was verified in this study. One sample from each rock unit was tested by static methods and also tested dynamically. The equation was accurate within 0.4-7.8$ deviation in calculation of the static

Modulus of Elasticity. Considering the variability in the initial determination of each constant, this error was 116 considered nominal and the equation was used to calculate the remaining static elastic constants. Test results are given in Table 5 and 6. STATIC ELASTIC CONSTANTS SRKIK AT ION

Evaluation of statin elastic constants generally employs the use of strain gages mounted on a cored rock specimen similiar to those used in the compressive strength test. Two gages are attached to measure the axial strain and two are attached to measure the transverse strain (Pig.

10 and Photo 34). Gage type EA-06-250AP-120 was used. Any change in the original gage resistance of 120-0. is converted to a corresponding strain which is plotted on the X~Y plotter. Since the gages are attached in series, the strain is divided by 2 to obtain the actual strain.

The specimen is uniaxially loaded (generally compressive for rock). The axial and transverse strains are recorded by means of the X-Y plotter via stress-strain calibration apparatus (Pig. 11 and Photo 35). From this data, the Elastic Modulus and Poisson's Ratio are cal­ culated according to ASTM (1972).

Test results are given in Table 6. 118

' i ''iw x ;i -■ 8M0LI I1AH3-3 fern-

Photo 34- Strain gages mounted on rock samples

m p m s E ^ w &&*sa *iv_

) ■ ' v&-'iVCi*.

^'.VV

55» Xfe • 't-'hi’.1-

Photo 33 Static Elastic Constants testing apparatus ^•a

Gage Diagram Showing Total Circumference of Rock

Rig, 10 Strain Gage Attachment 120

1 Compressive Unit 2 SBEL Bridge Box 5 SBEL Strain Gage Signal Conditioning System 4 E,P. 7005B X-Y Plotter

Pig. 11 Stress-Strain Testing Apparatus 121

DRILLABILITY

The drillability of a rock sample is simply described as the distance a drill bit is able to penetrate through a rock sample per unit time under a specific load.

In this study, a diamond coring bit was vised with an inside diameter of 2-1/8 inches (5*4 cm) or NX core size. A load of 35 'lbs (16 kg) was applied to the drill press which had a bit rotation of 1,000 rpm. Constant water flushing was used of 3/4 gallons/minute (0.17 m5/hr).

This parameter is rarely seen in the literature.

In this study, it is used to predict the compressive strength of a rock sample. Relationships are also shown between the drillability of a rock and its specific gravity and porosity.

Test results are given in Table 6. 122

CHAR ACT ERISTIC IMPEDANCE

The characteristic impedance o.f a medium through which a stress wave is transmitted is defined as the density- times the stress wave (P wave) velocity. The transfer of energy across any junction between one medium and another, across grain boundaries or pore spaces is affected by

conditions at the boundaries themselves. The tighter the grain boundaries or the less pore spaces present, the greater the characteristic impedance and the greater the compres­ sive strength or Modulus of Elasticity. The impedance of a rock is a very important parameter in estimation of blast­ ing criterion.

Test results are given in Table 7. BCB TOOL BMOL(M) BMOL(V) AHB(M) ARE(V) HOL ength, q 31,816 11 21,605 19,193 6,593 20,316 35,193 (psi) 1,919 145 4,862 1,487 1,016 1,582 2,950 tngth, q 219 149 132 45 140 37 (Nmm-2) 243 U 13 1 33 10 7 11 20 1, S.G. 2.69 2.76 2.72 2.31 2.62 2.04 2.77 0.01 0.01 0.02 0.01 0.02 0.08 0.04 , S.W. 167.8 172.2 169.7 144.1 163.5 127.3 172.8 (Ib/ft3) 0.6 0.6 1.2 0.6 1.2 4.9 2.5 Porosity, n 0.83 2.S5 5.6 16.8 4.1 21.4 1.56 (%) " 0.10 0.15 1.0 0.4 C.6 2. S 0.30 , V 17,800 .16,166 15,386 10,406 14,063 11,523 16,720 (ft/sec) P 547 1,133 743 478 541 322 1,713 rave velocit; , V 5.42 4.93 4.69 3.17 4.23 3.51 5.09 (km/sec) 1 0.17 0.35 0.23 0.15 0.16 0.10 0.52 rave velocit; , V 10,577 8,845 •9,400 6,799 8,265 6,165 9,790 (ft/sec) 383 975 401 120 835 258 861 :ave velocit; , V 3.22 s 2.69 2.86 2.06 2.52 1.88 2.99 (km/sec) 0.17 0.29 0.12 0.03 0.25 0.08 0.26 tamic Elasti< Modulus, E, 9.87 7.45 7.75 3.17 5.89 2.67 8.85 (x 1C)6 psi) d 0.7 1.51 0.43 0.14 0.95 0.33 1.69 Modulus, E. 3008 2270 2362 966 1795 814 2697 -2) C 213 460 131 43 290 100 515 s Ratio, u^ 0.227 0,287 0.327 0.275 0.210 0.294 0,237 d 0.005 0.02 0.01 0.05 0.04 0.04 0.01

5 Test Results on Rock Samples from the Lousetown Formation. Averages given above, standard devia cions are below. (M)=Massive Samples,(V)=Vesicular Samples Three rock samples were tested from each group,both massive and vesicular. BC3 TOOL EMOL(M) BMOL(V) ARB (M) AHB(V) H0L Dynamic Modulus of Rigidity, G, 4.03 2.91 10.1 1.41 2.41 1.02 3.57 (x 10°psi) Q 0.31 0.64 0.3 0.07 0.16 0.04 0.07 Dynamic Modulus of Rigidity, G, 1228 887 3078 430 734 311 1088 (Nmm ‘L ) u 94 195 91 21 49 12 21 Dynamic Bulk Modulus, K 6.01 5.76 2.89 1.53 3.70 2.26 5.68 (x 10Jpsi) 0.4 0.5 0.8 0.4 0.5 0.5 1.3 Dynamic Bulk Modulus, K 1831 1756 881 466 1128 689 1731 (Nmm“*^) u 122 152 244 123 152 152 396 Static Elastic Modulus, E 5.8 4.6 5,3 2.1 3.7 1.8 5.5 (x lO^psi) 0.4 0.9 0.1 0.7 0.1 0.1 1.1 Static Elastic Modulus, E 1768 1414 1584 640 3127 548 1685 (Ntnm-/-) 122 274 30 213. 6 30 335 P wave /S wave lab velocity 1.68 .1.83 1.69 1.53 1.70 1.86 1.69 ratio, V /V 0.01 0.07 P s 0.09 0.12 0.13 0.12 0.02 Wave attenuation, B 1.64 2.62 1.33 1.53 2.43 0.77 2.66 (x 10-1) 0.08 0.13 0.04 0.06 0.21 0.09 0.80 Driilability, D 0.033 0.20 0.35 2.05 0.54 0.83 0.52 (ft/hr) 0.006 0.03 0.21 0.15 0.08 0.21 0.07 Driilability, D 1.0 6.1 10.7 62.5 16.4 25.3 15.8 (cm/hr) 0.2 0.9 6.4 4.5 2.4 6.4 2.1 Point Load Index, I 1,983 1,375 s (50) 983 450 1,393 556 2,176 191 75 117 204 395 228- 470

Table 5 Test Results on Rock Samples from the Lousetown Formation. Averages given above, standard deviations given below. (M)=Massive Samples, (V)=Vesicular Samples Three rock samples were tested from each group, both massive and vesicular. RGB TCOL 3MGL (M) BHOL(V) AHB(M) AHB(V) HOL P wave impedance. PWI 2.93 2,78 1.85 1.50 2.30 1.46 2.89 (xiO° lb-ft 2sec -*-) 0.12 0.20 0.15 0.06 0.10 0.09 0.28 P wave impedance, PWI 1.45 1.35 0.90 0.73 1.12 0.71 1.41 i. gin-cm ^sec 0.06 0.09 0.07 0.03 0.04 0.04 0.17 Schmidt Rebound Value, SRV 51 28 30 33 32 33 55 0.9 1.2 2.1 1.2 1.9 1.3 4.3

Table 7 Test Results on Rock Samples from the Lousetown Formation. Averages given above, standard deviations given below. (M)=Massive Samples, (V)=Vesicular Samples Three rock samples were tested from each group, both massive and vesicular. 126

SECTION V

ROCK PROPERTY RELATIONSHIPS AND VESICULAR ROOK CLASSIFICATION were shown to be capable of predicting the compressive compressive the predicting of capable be to shown were the graphs are given beside the graphs and correlation correlation and graphs the beside given are graphs the tigated that were capable of reliably (with correlation correlation (with reliably of capable were that tigated ofiins r aegvnblwtebs-i curves. best-fit below.the given (r) are coefficients the of All sample. rock ofa Modulus Elastic and strength could be calculated in the field. Best fit equations for equations fit Best field.the in calculated be could strength (coefficient of correlation inparentheses); correlation of (coefficient strength deviate from actual compressive strength by less than an than less by strength compressive actual from deviate compressive the predicting 0.80) than greater coefficients By using the least-squares method for curve-fitting and aand curve-fitting for method least-squares the using By average of 9$«• of average strength, predicted compressive strength was shown to shown was strength compressive predicted strength, 16 values (except compressive strength and Elastic Modulus), andElastic strength compressive (except 16 values h'-J collected. samples rock the from study inthis calculated ormal cluao, aiu rltosiswr inves­ were relationships various calculator, rogrammahle fterltosis netgtd te following the investigated, relationships the Of Using these relationships to calculate compressive compressive calculate to relationships these Using ) on od Index Load Point 8) ) dr 7) inability A-3 Graph (0.921) velocity 4)wave P (0.926) PWI impedance, wave 3) P A-2 (0.954)Graph SRV Value, Rebound Schmidt 2) ) aevlct (0.894) velocity S 6)wave (0.910) S.G. gravity, specific 5) A total of 16 different rock properties were properties rock 16 different of total A ) ooiy n (0.968) n 1) porosity, ROOK PROPERTY RELATIONSHIPS PROPERTY ROOK Graph A-1 Graph Graph A-6 Graph A-5 Graph A-4 Graph Graph A-8 Graph A-7 Graph 1 27 128

The following parameters were shown to be capable of predicting the Elastic Modulus values (coefficient of correlation in parentheses):

1) S wave velocity vs. (0.982) Graph A-9 2) P wave velocity vs. E^ (0.975) Graph A-10 3) P wave impedance vs.-E (0.975) Graph A-11 4) S wave velocity vs. E (0.955) Graph A-12 5) P wave velocity vs. E (0.942) s Graph A-13 6) porosity, n, vs. E^ (0.930) Graph A-14 7) specific gravity, S. G. vs. E^ Graph A~15 8) Schmidt Rebound Value, SRV vs. EdGraph A-16 9) dr inability vs. E Graph A*-17 10) Point Load Index Graph A-18

Using these relationships to calculate Elastic Modulus,.predicted Elastic Modulus was shown to deviate from actual Elastic Modulus by an average of 12c/o.

High coefficients of correlation were found between

Elastic Moduli values (both and E8) and compressive strength (Graphs A~19 and A-20), This may be helpful if both E values and compressive strengths are first arrived at from correlation with other index parameters and then compared via these curves to further adjust the predicted values. Some of the relationships do not show linear correspondence or predictable curves, but exhibit curvi­ linear relationships, or at least trends, which may help j.n prediction of other properties, especially over certain ranges of values. 1 29

The wave attenuation, B, shows a correspondence with both porosity and specific gravity (Graphs A-21 and

A-22). Drillability shows a relationship to the specific gravity and porosity (Graphs A-23 and A-24). This may be helpful in estimation of drilling rates for engineering tunnelling pro;j eets.

Porosity is shown to be related to the P wave impedance (Graph A-25). This can be helpful in predicting blasting behavior of both massive and vesicular rocks.

Poisson's Ratio was shown to have no correlation to any of the test parameters,

Some relationships can also be used for other predictions. According to the graphs: (1) rock samples that do not plot on or near the P wave velocity vs. Schmidt Rebound Value curve (Graph 4-26), (2) values of

V /V , other than 1.60-1.75 on the specific gravity vs. p s Y /Ve plot (Graph A-27), or (3) P wave velocities below 13,000 ft/sec (about 4 km/sec) on the ? wave vs. specific gravity graph (Graph A-28); are indicative of vesicular rocks. The latter two relationships may be helpful in locating the presence of vesicular rocks at depth with the aid of geophysical equipment. Graph A-l Compressive Strength vs. Porosity

Porosity, n% 131 Graph A-2 Compressive Strength vs. SRV

5 30 35 40 45 50 Schmidt Rebound Value (SRV)

1.5 2.0 2.5 3.0 3.5 P-wave Impedence (PWI) Ib-ft sec xlO^ 40 Graph A-5 Compressive Strength vs.

•-- - —-- — -- ---5—— — - — ■---- — ~— + 2.0 2.5 Specific Gravity (S.G.) Graph A-6 Compressive Strength vs. S-Wave Velocity

q =5.915(V )-3.07xl04 u s r=0.894

f r . . , * " - - ...... ’ ■-•— o-.fr-n.~~.. w W <— «— -m -o fr

3 S-Wave Velocity (V ) xlO ft/sec ---~-——---— -- 10 20 30 40 q xlO psi u

2 ~*"~4 6 8 10 Elastic Modulus xl.0 psi 136 w?* w m k • f* -j t k rr r ;

137 138

Elastic Modulus xlO psi

Graph A-14 Elastic Modulus vs. Porosity

T ~r~ 5 10 15 20 Porositj' n% 139

Specific Gravity (S.G.)

E d=117066.8SRV+3702613 r=0.843

Drill-ability ft/hr •in 141

-+ ' T‘ 2 4 6 8 10 Elastic Modulus E xlOb psi s Graph A-20 Compressive Strength vs. Elastic Modulus «

------r------"~i"”--- --“— ™t 2 4 6 6 8 10 Elastic Modulus xlO psi 143

Porosity n% Drillibility ft/hr Drillibility ft/hr

147

270 “ ~~2.#5 Specific Gravity 148

STRENGTH OF VESICULAR BASALTS

The most important and the only investigation into

the strength of vesicular rocks was conducted hy button

(1969) in which he noticed the rapid reduction in strength of vesicular basalts with decreasing specific gravity. Although he suggests a mechanism for this drastic strength

reduction, he makes no attempt to predict the strength values

for these low specific gravity basalts. The author will attempt to continue with button's ideas.

As seen in Graph A-29., with a reduction in cross-

sectional area of only 20fot a corresponding reduction in compressive strength of about 75°/> occurs, button ( 1969) hypothesizes that this is caused by great "stress conver­ gence" through all 'vesicle partitions. The author will go further to state that this increased stress plus premature failure of certain areas where smaller than "average" par­ titions occur may lead to a "Domino-Effect" of partition- failures. Simply .stated, there may be certain areas of the rock that have thinner partitions than the specific gravity of the sample would indicate. These thinner par­ titions would have a lower failure stress relative to the other partitions. They would, of course, fail first, putting an even greater stress on the surrounding partitions, causing premature failure of the entire rock sample.

On Graph -A-29, the equation for the strength based on reduction of the sample’s cross sectional area, 149

Graph A-29 Compressive Strength vs. Specific Gravity

Average strength of massive basalts excluding high strength samples: qu=21,500 psi, and

------..... ------...------. . _ _ i ------— ------2.0 2.5 Z.7 Specific Gravity plotted in dashed lines. The equation is:

Compressive strength = -- Load Areasolid

2/3. Areasoiid = (Vol,,m9soiia)

2/3 (specific gravity of vesicular sample) ' (specific gravity of solids)'

(after Lutton, 1969)

The actual strength equation is noted on the Graph. 151

VESICULAR ROCK CLASSIFICATION

Once the vesicularity of a sample is calculated', the actual compressive strength may he predicted rather

crudely hy using Graph A-29. If a Schmidt Hammer is used

to determine the compressive strength, the predicted

strength would probably be much greater than the actual

strength because the Schmidt Rebound Value only measures the competency of the rock material without taking into

account the effect of the vesicles. For this reason, Graph

A-50 was developed. Finding or estimating the specific gravity or amount of vesicularity, plus the Schmidt Rebound

Value to obtain the predicted compressive strength, one may estimate the actual compressive strength. A classification system for vesicular rocks was devised to aid in the esti­ mation of vesicularity. The Franklin Point Load Strength Test was not found useful in prediction of vesicular rocks because of unpredictable vesicle interference.

Graph A-31 shows prediction of compressive strength for a. vesicular rock by way of porosity and/or specific gravity via the Schmidt Rebound Value. This was plotted from field test data. As shown, no matter how competent the rock sample may be (indicated by high Rebound Value), compressive strength is very small for samples with poros­ ity great ed than To summarize, Table 7 was developed for Schmidt 152

Hammer use. From the Schmidt Icebound Value and an estima­

tion of the vesicularity and/or specific gravity, predic­

tion of both the compressive strength and the Elastic

Modulus can be made. Vesicular rocks were placed in a

classification system according to their engineering

properties. Class I is the more competent, massive samples, while Class IV is highly vesicular with low compressive

strength and low Elastic Modulus. it of solids Graph A-30 Classification of Vesicular Basalts byBasalts ofVesicular Classification A-30 Graph and Specific Gravity Specific and Strength ofCompressive Reduction predicted compressive strength compressive predicted a ta opesv strength compressive ctual

Compressive Strength q _ xlC" psi 155

Table 8 Classification of Vesicular Basalts According to Engineering Properties

Class I Massive Rock: Specific Gravity 2.55 or greater Compressive Strength^ 17,000-45,000 psi

aCtUal n - i r 1 r\ q =0.75-1.0 predicted actual____ =0.9-1.0 predicted

Class II Slightly Vesicular: Specific Gravity 2.40-2.55 Compressive Strength=ll,000-17,000 psi

actual =o.5-o.75 predicted actual E ------=0.75-0.95 predicted

Class III Moderately Vesicular: Specific Gravity 2.15-2.4 Compressive Strength=6,000-11,000 psi

q actual =0.3-0.5 predicted actual =0.35-0.75 predicted

Class IV. Highly Vesicular: Specific Gravity less than 2.15 Compressive Strength= less than 6,000 psi actual =less than 0.3 predicted actual =less than 0.35 predicted A total of 16 different rock properties were

calculated from doth the massive and vesicular rocks of the Pleistocene Lousetown Formation of the Truckee Area.

For massive samples, 8 calculated properties were shown to be capable of predicting compressive strength. Of these, porosity and Schmidt Rebound Value have the highest coefficients of correlation.

Using all 8 relationships as shown in Graphs A-1 to A-8 , calculated compressive strength was shown to deviate

from actual compressive strength by less than an average 01 Sfo .

For massive samples, 10 calculated properties were

shown to be capable of predicting Elastic Modulus values.

Of these, S wave velocity, P wave velocity and P wave imped­ ance have the highest coefficients of correlation. Using all 10 relationships as shown in Graphs A-3 to A-18, calculated Elastic Modulus values were shown to deviate from actual values by an average of 12%.

Certain other curvilinear relationships, Graphs

A-21 to A-28, were shown to be helpful in other rock property predictions over all or certain ranges of values. For vesicular samples, a drastic strength reduction was shown to accompany decreasing specific gravity. As an aid in prediction of the compressive strength and Elastic

Modulus of a sample, the Schmidt Rebound Value (which is a measure of the competency of a rock) and an estimation 157

of the specific gravity and/or the porosity was shown to

be very useful, in that prediction.

A classification system was developed in which

compressive strength and Elastic Modulus values could be

obtained for each rock class from Glass I (massive rock) to Class IV (highly vesicular rock).

The relationships evolved in this study can be useful in the prediction of various engineering properties

of a rock mass as an estimate of design criterion, but

should not be used in lieu of a detailed site investigation

for engineering projects.

More work has to be done on the drastic reduction

of compressive strength with reduced cross-sectional area.

Effects that peed additional study as to their role during failure of a vesicular rock include: (1) possible stress

components due to arching effects around vesicules and (2) the little-known effect of the intermediate principal

stress component. .button ( 1969) has derived a two-dimensional analysis of the stress concentration factor around a vesicle. The equation shows that the stress in a vesicle wall can be increased by a factor of possibly as much as the ratio of the vesicle diameter plus the partition thickness divided by the partition thickness. This two­ 158 dimensional analysis is a gross simplification. As of now, empirical equations (such as derived in Graph A-29) and graphs that correlate field and laboratory test data (as in Graph A-31) approach the most accurate compressive strength prediction. Work to develop a three-dimensional model of vesicular rock failure is needed. SECTION VI APPENDIX GEOLOGIC TIME SCALE . MILLIONS OE YEAR ERA PERIOD EPOCH BEEORE PRESENT ' Holocene 0.01 Quat ernary Pleistocene 1.7-2.0

Pliocene 5-6 Cenozoie Miocene 25-27 Tertiary Oli&ocene 37-59

Eocene 53-54

Paleocene 63 Cretaceous 136-138

Mesozoic Jurassic 190-195 Triassic 225

Permian 270-280 P enn s yl v an i an 345-350

Mississippian 345-350 Paleozoic Devonian 3.95-420

Silurian 440-450

Ordovician 500

Cambrian 570 '

Pre camor ian UNIFIED SOIL CLASSIFICATION INCLUDING IDENTIFICATION AMD DESCRIPTION INFORMATION REQUIRED FOR | GROUP TYPICAL NAMES FIELD IDENTIFICATION PROCEDURES SYMBOLS DESCRIBING SOILS cies loi-ge.-uN'O" S inenes oni basin} Iroc'ior.s on *5timofe

Give typical ncm e: indicate approximate Well graded grovels, grovel-sand m ixtures, Je range :p groin si:e ond substantial amounts percentages of sand ord gravel-, mdx. iittle or no fines. ot clhnterm ediaf e particle? sizes S'Z“ ; angularity, surface condition, and hardness of the coarse grains-, r w o ® i . Poorly graded gravels, grovel-sand m ixtures, local or geologic name and other ] ^ ^ £ i predominant*/ ore sue ore renge o* sues pertinent descriptive inform ation; 1 < “ **" l with some intermediate sizes missing. little or r.o fines. and symbol in porenrheses.

Silty gravels, poorly graded gravel-sand- fjon-plcsric fines (for identification procedures silt m ixtures. see ML below).

For undisturbed soils add inform ation ayey gravels, poorly graded gravel* sard- on stratification, degree of compact­ cloy m ixtures. ness cementation, moisture conditions and drainage characteristics.

.Veil graded sands, gravelly sands; little or n o f ir e s . EXAMPLEs- Poorly graded sands, gravelly sands-, little or SMty sand, g ra ve lly; about 20 V. hard, n o f in e s . angular gravel particles j-in . maximal size-, rounded end subangular sand grains coarse to tine; about 15% r.or- Silty sands, poorly graded sand-silt m ixtures. plast'C fines with low dry strength; well compacted and m oist in place; a llu v ia l s a n d ; (S M ) Clayey sands, poorly graded sand-clay m ixtures.

Inorganic silts and'very tine sands, rock Hour, silty G:ve typical nam e; indicate degree and or clcyey fine sends with slight plasticity. character of plasticity, amount and maximum size of coarse grains-,color in wet condition , odor if any, local or Inorganic cloys of low to medium plasticity, gravelly geologic name, or.d other pertinent clays, sandy clays, silty clays, lean cloys. descriptive inform ation; and symbol in parentheses.

Organic silts and organic silt-c'ays of low For undisturbed soils add inform ation plasticity. on structure, stratification,consistency in undisturbed and remolded states, m oisture and drainage conditions. Inorganic silts, micaceous or diotomaceous fine sandy or silty soils, ulus’ ic sills. EXAUPLE:- Cloyoy silt, brown-, slightly plastic; Inorganic clays of high plasticity, fat cloys. :,muil percentage of fine sand; numerous vertical root holes; firm and dry in place-, ICC$S;(ML) CT\ Organic clays of medium ro high plasticity.

P tci end other highly organic soils. ■ rw p r- 555 REFERENCES - T V ^ 0E3 )555 A s i a , 1969, 332845-69, Standard and°uit?Soaic S ^ a ^ o f r o l ^ P. 356-565.

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