A GEOTECHNICAL INVESTIGATION OF THE OCTOBER 2011 CEDAR CITY LANDSLIDE, UTAH

A thesis submitted to the Kent State University Graduate College in partial fulfillment of the requirements for the degree of Master of Science

by

Ashley S. Tizzano

May, 2014

Thesis written by

Ashley S. Tizzano

B.S. Kent State University, 2010

M.S. Kent State University, 2014

Approved by

Dr. Abdul Shakoor, Advisor

Dr. Daniel Holm, Chair, Department of Geology

Dr. Janis Crowther, Dean, College of Arts and Sciences

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TABLE OF CONTENTS

Page

List of Figures……………………………………………………………………….……………vi

List of Tables……………………………………………………………………………………...ix

Acknowledgements…………………………………………………………..…………………….x

Summary...………..………………………………………………….…………………………….1

CHAPTER

1 INTRODUCTION……………………………...………………………………...3

1.1 The Cedar City Landslide…………….………...…………………………..3

1.2 Landslide Hazards in the Cedar Canyon………….……………………...... 8

1.3 Geology of the Area…...... …………………..………………..……...8

1.4 Research Hypothesis……………………………….…………………...…11

1.5 Objectives....…………….…………………………………………...……11

2 METHODOLOGY…………………………………………………………...…13

2.1 Field Investigations……………………………………………...………...13

2.1.1 Discontinuity Mapping...... 13

2.1.2 Subsurface Investigations………………….……...……..…...….16

2.2 Laboratory Investigations……………………………………...………….18

2.2.1 Grain Size Distribution Analysis……………..………………….18

2.2.2 Natural Water Content Test……………………………………...19

2.2.3 Atterberg Limits Test……………………………………..……...19

2.2.4 Absorption Test……………………………….…………………20

2.2.5 Slake Durability Test…………………..………………………...21 iii

2.2.6 Unconfined Compression Test…………………………………..21

2.2.7 Direct Shear Test.………………………………..……………….22

2.3 Data Analysis…………………………………………………………...…24

3 DATA ANALYSIS AND INTERPRETATION…………………...…………...25

3.1 Field Observations…………………………………………………….…..25

3.2 Discontinuity Data…………………………………………………...……25

3.3 Subsurface Data………………………………………………………...…29

3.4 Engineering Properties of the Colluvial Soil and Bedrock Units.....…...…32

3.4.1 Grain Size Distribution…………………………………………...32

3.4.2 Natural Water Content and Bulk Density………………...………35

3.4.3 Atterberg Limits…………………………………………………..35

3.4.4 Dry Density, Absorption, Slake Durability, and Unconfined Compressive Strength for Bedrock Units.....…………………….35

3.4.5 Shear Strength Parameters………………………………………..40

4 STABILITY ANALYSIS OF THE CEDAR CITY LANDSLIDE….………….42

4.1 Landslide Type and Failure Plane Location Used for Stability Analysis....42

4.2 Input Parameters for Stability Analysis…..……………………………….43

4.3 Stability Analysis Using the SLIDE Software Program…………………..46

4.4 Causes of the Landslide…………………………………………………...59

5 REMEDIAL MEASURES……………………………………………………...61

6 AN OVERVIEW OF SLOPE STABILITY HAZARDS IN CEDAR

CANYON………………..……………………………………………………...70

7 CONCLUSIONS………………………………………………………………..80

REFERENCES………………………………………………………………………………...... 82

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APPENDICES

A: Discontinuities…………………………………………………………………..85

B: Borehole Logs, Inclinometer Data, Geophysical Survey, and Rainfall Data.…..90

C: Laboratory Data………………………………………………………………..115

D: Stability Analysis………………………………………………………………180

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LIST OF FIGURES

Figure 1.1 Location map of the Cedar City landslide……………..…………………………4

Figure 1.2 An aerial view of the Cedar City landslide …………………………………..…..5

Figure 1.3 Close up view of the head area of the landslide ……..…………………………..5

Figure 1.4 Panoramic view of the landslide and the Cedar Canyon ………………………...6

Figure 1.5 Displaced portions of SR 14 on the east side of the landslide …………………...6

Figure 1.6 Landslide material covering SR 14 on the west side of the landslide ..………….7

Figure 1.7 Slope hazard history of Cedar Canyon…………………………………...………9

Figure 1.8 Stratigraphic column for the Cedar Canyon...…………………………………..10

Figure 2.1 Discontinuities within the Dakota Sandstone…………………………...………14

Figure 2.2 Discontinuities within the Straight Cliffs Sandstone…………………………....15

Figure 2.3 Location map of the boreholes drilled…………………………………………..17

Figure 2.4 Relation between Schmidt hammer rebound number and unconfined compressive strength of rocks ………………………………………………………..………23

Figure 3.1 Contouring of Straight Cliffs Sandstone discontinuities using the DIPS software ..…...... 26

Figure 3.2 Contouring of Dakota Sandstone discontinuities using the DIPS software……..27

Figure 3.3 Contouring of discontinuities from both the Dakota Sandstone and the Straight Cliffs Sandstone using the DIPS software ………………..…………………….28

Figure 3.4 Evidence of water runoff over the slope face comprised of the Dakota Sandstone ...... 30

Figure 3.5 Cumulative displacement from the inclinometer data obtained from borehole 8-2 ..…………………………………………………………………………………33

Figure 3.6 Grain Size Distribution curve for sample 4 of the colluvial soil...... ………….34

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Figure 3.7 A plot of Atterberg limits on Casagrande’s plasticity chart showing that the fines are classified as low plasticity clay …………...... ……..36

Figure 4.1 Cross-section created for stability analysis...... 44

Figure 4.2 Geological Strength Index (GSI) chart……………………………………...... 45

Figure 4.3 Stability analysis for dry colluvial soil-Tropic Shale parameters, using both Bishop and the Janbu Simplified methods……...…………………………...…..47

Figure 4.4 Stability analysis for dry colluvial soil-Dakota Sandstone parameters, using both Bishop and the Janbu Simplified methods……………………………………...48

Figure 4.5 Stability analysis for the averaged dry colluvial soil-bedrock parameters, using the Bishop Simplified method...………………………………………………...49

Figure 4.6 Stability analysis for fully saturated colluvial soil-Tropic Shale parameters, using both Bishop and the Janbu Simplified methods.....……………………………...50

Figure 4.7 Stability analysis for fully saturated colluvial soil-Dakota Sandstone and the average soil-bedrock parameters, using both Bishop and the Janbu Simplified methods………………………………………………………………………….51

Figure 4.8 Stability analysis with the maximum water table height at 3.3 ft (1 m) above the contact, Φrequired = 29°…………………………………………………………....53

Figure 4.9 Stability analysis with the maximum water table height at 11.7 ft (3.5 m) above

the contact, Φrequired = 30°…………………………………………………...54

Figure 4.10 Stability analysis with the maximum water table height at 23.7 ft (7.2 m) above the contact, Φrequired = 32°….……………………………………..……………...55

Figure 4.11 Stability analysis with the maximum water table height at 39.4 ft (11.9 m) above the contact, Φrequired = 34°………………………………………………………..56

Figure 4.12 Variation of back-calculated friction angle for varying heights of water table, for a safety factor of one…………………………………………………………….57

Figure 4.13 Geologic cross-section used for stability analysis showing the level of water encountered in Borehole 8-2...... 58

Figure 4.14 Daily precipitation outside Cedar City, UT from September 1st to October 31st, 2011……………………………………………………………………………..60

Figure 5.1 Regraded slope above the road and riprap-filled drainage ditch……………..…62

Figure 5.2 Scaling of the Straight Cliffs Sandstone above the road………………………..62

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Figure 5.3 East side view of the modular block retaining wall .……………………………64

Figure 5.4 West side view of the modular block retaining wall.…………………………...65

Figure 5.5 Smooth wheel roller compacting subgrade material for reconstruction of SR 14………………………………………………………………………………..65

Figure 5.6 View of the riprap filled ditch and road from slope above………...……………66

Figure 5.7 Aerial view of the repaired landslide and SR 14 …..…………………………...66

Figure 5.8 Riprap filled drainage ditch and the newly paved SR 14 .……………………...67

Figure 6.1 Unfavorably oriented joints within the Straight Cliffs Sandstone in the Cedar Canyon showing the potential for a variety of slope movements ....……………71

Figure 6.2 Jointed nature of the Straight Cliffs Sandstone, resulting in a blocky nature of the rock mass and a potential for rockfalls and other types of slope movement……72

Figure 6.3 Potential for rockfall hazard along discontinuities in the Straight Cliffs Sandstone …………………………………………………………………...……………...73

Figure 6.4 Valley stress relief joints along the Cedar Canyon wall showing the potential for rockfalls and plane failures ……………………………………………………..74

Figure 6.5 Debris from previous rockfalls in the canyon ………...………………………...75

Figure 6.6 Source area for the 2012 rockfall above SR 14 ………………………………...76

Figure 6.7 Rockfall debris on SR 14.……………………………………………………….76

Figure 6.8 Damage to SR 14 from 2012 rockfall ………………...………………………...77

Figure 6.9 Kinematic analysis using the RockPack 3 software, based on measured discontinuities within the Straight Cliffs Sandstone ……...…………………….78

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LIST OF TABLES

Table 3.1 Average Atterberg limits from the colluvial soil………….…………………….34

Table 3.2 Summary of dry density, absorption, slake durability, and unconfined compressive strength data for the bedrock units involved in the Cedar City landslide…...... 37

Table 3.3 Two-cycle slake durability classification………………..……………………...37

Table 3.4 Engineering classification of intact rock…………..……………………………41

Table 3.5 Summary of the shear strength parameters for the colluvial soil and the soil- bedrock contact…………………………….……………………………………41

Table 4.1 Parameters used for stability analysis scenarios………………………………...45

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ACKNOWLEDGEMENTS

I would first like to thank my adviser, Dr. Abdul Shakoor, for his patience, guidance, and support throughout my project. I have learned so much from you over the years, including how important it is to do what you love. Thank you.

I would also like to thank my committee members, Dr. David Hacker and Dr. Daniel

Holm for their valuable contributions and keeping me on track.

I am deeply grateful to the Utah Department of Transportation (UDOT), especially Keith

Brown, Dave Fadling, and Sam Grimshaw, for giving me permission to work on this project, take measurements and photos while they were repairing the landslide, and giving me their data from the subsurface investigations and the remediation plans for State Route 14. I am also thankful for all the assistance given by Bill Lund and Tyler Knudsen from the Utah Geological Survey (UGS), by allowing me to borrow equipment and access to unpublished maps, storing my samples, and keeping me up to date on hazards along SR 14.

I acknowledge the great help I received from Nate Saraceno, Matt Waugh, and Yonathan

Admassu during the laboratory and data analysis phases of the project. I offer special thanks to my sister, Rachael Tizzano, for driving cross-country with me to be my field assistant. I appreciate all the support I got from my friends and classmates, Chelsea Lyle, Natalie Cope,

Nidal Atallah, Emine Onur, and Mike Glassmeyer.

I want to extend my deepest gratitude to Chelsea Windus, Tommy Schneider, and my mother, Susan Miller. Your encouragement kept me going through my project and reminded me of my goal. I cannot thank you enough.

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SUMMARY

During the morning of October 8, 2011, a massive landslide caused severe damage to State Route 14 (SR 14) in Cedar Canyon, eight miles outside Cedar City,

Utah. The landslide detached approximately 1.5 million cubic yards of material from the south side of the canyon, displaced parts of the road and covered the remainder of a 1200 ft (365 m) stretch of SR 14 under more than 100 ft (30 m) thick debris. The stratigraphy of the canyon where the landslide occurred includes the cliff-forming Tibbet Canyon

Member of the Straight Cliffs Formation (limey sandstone) and the underlying slope- forming Tropic Formation (shale) and Dakota Formation (mudstone and sandstone with coal horizons), all Cretaceous in age. The landslide initiated in the Straight Cliffs

Sandstone and propagated as a translational slide along the contact between the colluvial soil and the underlying bedrock. Utah Department of Transportation (UDOT) drilled three borings through the landslide material, placed slope inclinometers in the borings, and conducted a geophysical survey from the crest to the toe of the slide. I used detailed line survey and window mapping methods to collect orientation data for 186 discontinuities within the Straight Cliffs and Dakota Sandstones. Stereonet plots of discontinuity orientation data, generated by the DIPS software, revealed the presence of three principal joint sets that contribute to slope instability at the site. Samples of the colluvial soil and the bedrock were tested in the laboratory to determine relevant engineering properties including natural water content, density, and shear strength

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parameters (cohesion and friction) of soil, bedrock, and soil-bedrock contact. The SLIDE software program and data generated in the laboratory were used to perform a stability analysis which indicated a factor of safety of 0.8 to 1.2 for the dry conditions and 0.3 to

0.4 for fully saturated conditions (water table at ground level). A sensitivity analysis was performed by adjusting the water table height to create partially saturated soils and determining the friction angle needed for a safety factor of one, keeping the cohesion value as determined in the laboratory. For an average friction angle value of 29o, a water table height of approximately 3.3 ft (1 m) above the soil-bedrock contact is required to cause the failure; however, it may be slightly different than that depending on the type of bedrock lithology (shale, mudstone, sandstone) controlling the failure. The results of this study show that a combination of factors was responsible for causing the Cedar City landslide including a relatively steep colluvial soil slope (~30°), extra weight on the soil from previous rockfalls, and buildup of pore pressure due to a rainstorm prior to failure.

Remedial measures used by UDOT to stabilize and repair SR14 include re-grading the slope of the failed colluvial soil to 2H:1V, placing a riprap-filled ditch along the road for drainage purposes, installing a retaining wall below the road on the east side of the landslide, re-compacting the subgrade material under the road and reconstructing the pavement.

CHAPTER 1

INTRODUCTION

1.1 The Cedar City Landslide

During the morning of October 8, 2011, a massive landslide caused extensive damage to State Route 14 (SR 14), eight miles outside Cedar City, Utah (Figure 1.1). SR

14 is an important transportation route between Interstate 15 in Cedar City and U.S.

Highway 89 to the east (Lund et al., 2009). The landslide detached approximately 1.5 million cubic yards (1.1 million m3) of material from the south side of the canyon

(Figures 1.2, 1.3, and 1.4), displaced parts of SR 14 (Figure 1.5) and covered a 1200 ft

(365 m) stretch of the road with slide debris (Figures 1.2, 1.4, and 1.6) (Lund et al.,

2011).

Utah Department of Transportation (UDOT) was responsible for the repair and reconstruction of SR 14. Prior to construction, UDOT drilled three boreholes and placed slope inclinometers within them. AMEC, a geotechnical firm, was hired to conduct a geophysical survey along the toe of the landslide.

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Figure 1.1: Location map of the Cedar City landslide (http://www.merriam-webster.com/cgi-bin/nytmaps.pl?utah, Google Earth).

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Figure 1.2: An aerial view of the Cedar City landslide (UDOT, 2011).

Figure 1.3: Close up view of the head area of the landslide (UDOT, 2011).

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Figure 1.4: Panoramic view of the landslide and the Cedar Canyon (UDOT, 2011).

Figure 1.5: Displaced portions of SR 14 on the east side of the landslide (UDOT, 2011).

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Figure 1.6: Landslide material covering SR 14 on the west side of the landslide.

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1.2 Landslide Hazards in the Cedar Canyon

Utah is in a group of eight states with a landslide hazard rating of “severe”, the highest hazard class, based on landslide damage and costs incurred within the decade

1979 –1989 (Brabb, 1989). Conditions favorable to landslide activity exist primarily in mountain ranges and along the edges of high plateaus (Harty, 1991).

Cedar Canyon is a highly hazardous area with a history of landslides, rockfalls, and debris flows, all of which can be seen in Figure 1.7. The earliest record of landslide occurrence in Cedar Canyon is in the November 24, 1915 edition of Parowan Times which mentioned a large landslide stopping travel through the canyon. In March 1989, another large landslide affected SR 14, having a volume of approximately 2 million cubic yards (1.5 million m3). This landslide occurred below the road and carried it down slope

(Harty, 1989). There was a debris flow in 2005, littering the edges of the valley with trees brought down from miles away (Giraud and Lund, 2005). In 2009, a large rockfall buried

SR 14 under tens of individual large boulders and hundreds of smaller boulders (Lund et al., 2009).

1.3 Geology of the Area

In eastern Iron County, the location of the Cedar Canyon, the Cretaceous is by far the most extensive of the major stratigraphic units of Mesozoic age (Gregory, 1950). The stratigraphy of the Cedar Canyon, where the landslide occurred, includes the cliff- forming Tibbet Canyon Member of the Straight Cliffs Formation and the underlying slope-forming Tropic Formation and Dakota Formation, all Cretaceous in age.

Figure 1.7: Slope hazard history of Cedar Canyon (Lund, 2011).

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Figure 1.8: Stratigraphic column for the Cedar Canyon. The units involved in the landslide are boxed in yellow (Erskine et al., 2001)

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(Figure 1.8). The Tibbet Canyon Member is 600 ft (183 m) thick and consists dominantly of fine to coarse grained, limey sandstone (Lund, 2011) and minor interbedded grey mudstones and siltstones (Biek et al., 2011). The Tropic Shale consists of ~30 ft (9.1 m) of sandy mudstone and muddy sandstone (Lund, 2011). Topographically, the Tropic

Formation occurs as slopes of moderate inclination on which disintegration products and the debris from landslides are so thickly piled that exposures suitable for detailed study are rare (Gregory, 1950). The Dakota Formation is over 600 ft (183 m) thick and mostly interbedded mudstone and sandy mudstone with thin sandstone and several ft (~3 m) thick coal horizons (Lund, 2011) and is considered both a slope and ledge forming sandstone (Biek et al., 2011). The Tropic Shale and Dakota Sandstone are undivided in

Cedar Canyon where the Tropic Shale is a few feet to at most 30 ft (1 m-9.1 m) thick

(Biek et al., 2011).

1.4 Research Hypothesis

The hypothesis of this research is that the Cedar City landslide initiated as a rotational movement near the scarp and transformed into a translational failure downslope, along the colluvial soil-bedrock contact.

1.5 Objectives

The main objectives of this research were as follows:

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1. Determine the type of the Cedar City landslide, causes of the landslide, and the

location of the failure plane.

2. Determine the engineering properties of the colluvial soil and bedrock units involved

in sliding.

3. Perform a stability analysis.

CHAPTER 2

METHODOLOGY

2.1 Field Investigations

2.1.1 Discontinuity Mapping

A combination of the detailed line survey method, developed by Piteau and

Martin (1977), and the window mapping method, described in Wyllie and Mah (2004), was used to map discontinuities within the bedrock units involved in sliding. The window mapping method was used because the detailed line survey method alone can miss the horizontal discontinuities parallel to the survey line (Park and West, 2002). The detailed line survey method consists of stretching a 100 ft (30 m) long measuring tape along an outcrop and measuring all discontinuities that intercept the tape. The window mapping uses a 20 ft by 20 ft (6 m by 6 m) square ‘window’ to measure the discontinuities. Both methods provide orientation and spacing data for the discontinuity sets measured. The discontinuities were measured in the vicinity of the actual landslide because the hazardous nature of the Straight Cliffs Sandstone at the actual site of the Cedar City landslide. In addition to collecting orientation and spacing data for the bedrock discontinuities, other aspects of the joints (continuity, aperture, surface irregularities,

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Figure 2.1: Discontinuities within the Dakota Sandstone.

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Figure 2.2: Discontinuities within the Straight Cliffs Sandstone.

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nature of infilling material, etc.) were observed and recorded. Figures 2.1 and 2.2 show the joint sets within the bedrock that were measured. Discontinuity data were used to evaluate the potential modes of failure affecting the bedrock at the study site. Debris from these failures accumulates on the slope, adding to the gravitational forces. Appendix A provides the discontinuity measurement data.

Alongside discontinuity mapping, samples of colluvial material and the bedrock units, involved in landsliding, were collected for laboratory testing. Additionally, photographs of the canyon walls and various stages of remediation were taken.

2.1.2 Subsurface Investigations

Detailed subsurface investigations were conducted by UDOT, through contractors, to determine the remediation needed to repair SR 14 from the landslide damage. RayCon drilling company was hired to drill three boreholes, two on the landslide at mile marker 8 and one outside of the landslide area around mile 7.5 (Figure

2.3). The borings were drilled to depths ranging from 75 ft (23 m) at the toe to 171 ft (52 m) near the head of the landslide. Slope inclinometers were placed in each borehole to monitor any movement within the landslide. Appendix B includes the logs for the three boreholes. In addition to borings, a geophysical survey, using surface seismic Refraction

Microtremor (ReMi) and SmartSeis SE-24 seismograph, was conducted by AMEC, a multinational geotechnical company. Eight survey lines, 240 ft (73 m) long, were chosen along the length of the slide, approximately perpendicular to the sliding direction to determine the depth to bedrock and possible location of the failure plane.

Figure 2.3: Locations of the boreholes drilled (Google Earth, USGS).

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2.2 Laboratory Investigations

Core samples, obtained from UDOT, as well as colluvial soil and bedrock samples, collected in the field, were used for laboratory testing. The laboratory tests conducted included determination of natural water content, grain size distribution,

Atterberg limits, specific gravity, absorption, slake durability, unconfined compressive strength, tensile strength, and shear strength parameters. All tests were conducted using standard procedures specified by the American Society for Testing and Materials

(ASTM) (ASTM, 1996). Appendix C provides the results of laboratory tests.

2.2.1 Grain Size Distribution Analysis

Grain size distribution analysis of the colluvial soil, comprising the landslide material, was performed using the ASTM method C136 (ASTM, 1996). The sieves used in the analysis included numbers 4, 10, 40, 100, and 200. Each sieve was weighed prior to the analysis. The soil was shaken for 15 minutes and percentage of the material passing each sieve was determined. The sieve analysis data were plotted as grain size distribution curve which was used to determine coefficient of uniformity and coefficient of curvature, the quantitative indices of grain size distribution. The coefficient of uniformity (Cu) is expressed by:

Cu = D60 / D10

The coefficient of curvature (Cc) is expressed by:

2 Cc = (D30) / (D10*D60)

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Where:

D10 = diameter that corresponds to 10% passing

D30 = diameter that corresponds to 30% passing

D60 = diameter that corresponds to 60% passing

Four grain size distribution analyses were performed and averaged. The results of the grain size distribution analysis were used to classify the colluvial soil according to the

Unified Soil Classification System (USCS), as described in Holtz et al. (2011).

2.2.2 Natural Water Content Test

Natural water content of the landslide material was determined in the laboratory using the ASTM method D2216 (ASTM, 1996). A wet sample, weighing 500 g was oven dried for 24 hours, allowed to cool to room temperature, and weighed again.

Using the weight of water in the soil, natural water content was calculated as follows:

Natural Water Content (%) = (weight of water / dry weight of soil)*100

2.2.3 Atterberg Limits

Atterberg limits are the water contents at which marked changes in the engineering behavior of fine grained soils occur. Liquid limit (LL) is the lower limit of water content at which a soil behaves as a viscous liquid. Plastic limit (PL) is the lower limit of water content at which a soil behaves plastically. Plasticity index (PI) indicates the range of water contents over which a soil behaves as a plastic material and is defined

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as the difference between the liquid limit and plastic limit (Holtz et al., 2011). The

Atterberg limits for the landslide material were determined according to the ASTM procedure D4318 (ASTM, 1996). The samples for this test were prepared by oven drying the soil and passing it through sieve # 200, until 200 g of sample was collected. Liquid limit is the water content at which 25 blows are required to close the groove in a soil pat for ½” (12.7 mm) length in the standard test. Plastic limit is the water content at which a

3 thread of soil crumbles into segments /8” – ½” (9.53 mm - 12.7 mm) when rolled to 1/8"

(3.18 mm) thickness. Three tests were performed to determine the liquid limit and plastic limit values. The Atterberg limits were used to classify the fine-grained portion of the colluvial soil according to the USCS (Holtz et al., 2011).

2.2.4 Absorption Test

The amount of water absorbed by a rock is an indicator of its void space and its strength (Shakoor and Barefield, 2009). The absorption test was conducted in accordance with ASTM procedure D4473 (ASTM, 1996). Three pieces of each rock unit involved in sliding were submerged in water for 24 hours. After 24 hours, each sample was blotted to remove surface water and weighed to get the saturated weight. The samples were oven dried for 24 hours, cooled to room temperature, and weighed to determine the dry weight.

The percent absorption was determined using the following equation:

Absorption = {(wet weight – dry weight) / dry weight}*100

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2.2.5 Slake Durability Test

The slake durability test was conducted on the weaker, argillaceous bedrock units using ASTM procedure D4644 (ASTM, 1996). The slake durability index provides a quantitative measure of resistance to weathering. Three tests were performed for the

Tropic Shale and three for the Dakota Sandstone. The sample for the slake durability test consisted of 10–12 pieces of rock, weighing 40–60 g each, with a total weight of approximately 500 g. The sample was placed in a wire mesh drum and rotated in a water tank for 10 minutes at 20 rotations per minute. The remaining sample in the drum was oven dried for 24 hours and weighed. All samples were slaked over two cycles and the

nd 2 cycle slake durability index (Id2) was calculated as:

Id2 = (Dry weight after cycle 2 / Initial dry weight)*100

2.2.6 Unconfined Compression Test

The unconfined compression test was conducted on core samples of Dakota

Sandstone, provided by UDOT, to characterize their strength behavior. ASTM method

D2166 (ASTM, 1996) was used to conduct the test. Each core sample was failed axially in 5 to 15 minutes at an average rate of 1125 lbs/min (511.4 kg/min). The unconfined compressive strength (qu) was calculated as failure load divided by the sample area. Four core samples were tested in unconfined compression and the average values were obtained.

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No core samples were available for the Straight Cliffs Sandstone, so the Schmidt

Hammer was used to obtain the unconfined compressive strength. Ten measurements of rebound number were taken and averaged. Figure 2.4, from Deere and Miller (1966), was used to determine the unconfined compressive strength from the rebound number.

2.2.7 Direct Shear Test

The shear strength parameters, cohesion and friction angle, of colluvial soil and the bedrock units around the failure plane were determined using the direct shear test in accordance with the ASTM procedure D3080 (ASTM, 1996). The shear strength parameters determined were used in stability analysis of the failed slope. To determine the shear strength parameters of the colluvial soil, the blow counts from the borehole logs were used to figure out the in situ density. The shear box dimensions were measured and the mass of soil needed to achieve the in situ density was calculated.

Before testing, the colluvial soil was oven dried for 24 hours and only the material passing the number 10 sieve was used in the test. Three tests were conducted on dry soil and three on soil at natural water content (NWC). The direct shear test was also conducted with the failure plane along the soil/bedrock contact. Slabs of the Dakota

Sandstone and Tropic Shale were cut to fit into the lower half of the shear box and the colluvial soil in the upper half. Three tests were run for dry soil/sandstone, three tests for

NWC soil/sandstone, and three tests for dry soil/shale.

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Figure 2.4: Relation between Schmidt hammer rebound number and unconfined compressive strength of rocks (Deere and Miller, 1966).

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2.3 Stability Analysis

Using the shear strength parameters for the bedrock and soil, as determined in the laboratory, the SLIDE program (Rocscience, 2003) was used to determine the factor of safety against sliding. The slope profile was created using a topographic map and the subsurface was interpolated from borehole logs, geophysical surveys, and a geologic map of the area. The cross section was recreated in SLIDE. The program ran non circular analysis (failure along soil-bedrock contact) for dry and saturated conditions, as well as varying heights of the water table. The calculations are presented in Appendix D.

CHAPTER 3

DATA ANALYSIS AND INTERPRETATION

3.1 Field Observations

The Cedar City Landslide is approximately 1000 ft (303 m) long and up to 1700 ft

(515 m) wide (Lund, 2011). The length is defined as the minimum distance from the toe of the landslide to the crown and the width is defined as the maximum breadth of the displaced mass perpendicular to the length (Cruden and Varnes, 1996). The head scarp is located in the Straight Cliffs Sandstone, with the largest exposure measuring approximately 50 ft (15 m) in height. The landslide material is comprised of mainly colluvial soil with boulders of the overlying Straight Cliffs Sandstone. Field observations, subsurface drilling, and geophysical survey suggest that the landslide occurred along the colluvial soil-bedrock (Tropic Shale/Dakota Sandstone) contact.

3.2 Discontinuity Data

Discontinuity orientation data for the bedrock units were plotted on stereonets as poles and contoured to determine the principal joint sets, using the DIPS software

(Rocscience, 2003). Figures 3.1 through 3.3 show the contoured stereonets. The figures

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Figure 3.1: Contouring of Straight Cliffs Sandstone discontinuities using the DIPS software (Rocscience, 2003).

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Figure 3.2: Contouring of Dakota Sandstone discontinuities using the DIPS software (Rocscience, 2003).

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Figure 3.3: Contouring of discontinuities from both the Dakota Sandstone and the Straight Cliffs Sandstone using the DIPS software (Rocscience, 2003).

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show the presence of three principal joint sets, in addition to the bedding. The bedding has an average dip direction of 186° and an average dip angle of 4°. Joint set 1 is a near vertical joint set (88°) with an average dip direction of 149°. Joint set 2 is a valley stress relief joint with an average dip direction of 30° and an average dip angle of 84°. Joint set

3 has an average dip direction of 276° and an average dip angle of 89°. The spacing between the discontinuities ranges from one inch (2.5 cm) to 8 ft (2.4 m). The infilling material present in the open joints consists of material eroded from the surrounding rock and is very weak in nature (easily brushed off). Field observations showed evidence of water runoff on the slope face (Figure 3.4), but discontinuities were found to be dry. The joints in Dakota Sandstone are relatively smooth and straight whereas those in the

Straight Cliffs Sandstone are very rough and undulatory.

3.3 Subsurface Data

Three boreholes were drilled at the landslide site for subsurface investigations and were designated as 8-1, 8-2, and 7-5 because of their proximity to mile markers 8 and 7.5 along SR 14 (Figure 2.3) Borehole 8-1 was drilled to a depth of 171 ft (51.8 m) near the head scarp area of the landslide. The landslide deposit had boulders of sandstone in a matrix of sand, silt, and clay, which UDOT classified as silty sand to low plasticity clay

(SM to CL). The average blow count for the colluvial soil was found to be 12, which was used to determine the in situ density for laboratory tests. The soil was very moist at 95 ft

(28.8 m) depth. Soft to very soft, dark grey shale to siltstone was encountered at a depth

of 147 ft (44.8 m). At 163 ft (49.4 m) depth, light grey, silty, fine-grained sandstone with 36

30

Figure 3.4: Evidence of water runoff over the slope face comprised of the Dakota Sandstone.

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coal seams was found and interpreted to be Tropic Shale and Dakota Formation undivided (Ktd). No shear zones were encountered within the colluvial soil or the underlying bedrock. The water table was not encountered during drilling of this borehole.

A 2.75 inch (7 cm) diameter Geokon inclinometer casing was placed in the borehole to a depth of 170 ft (51.5 m) and a sand slurry backfill was poured from 171 ft (51.8 m) to 38 ft (11.5 m) depth interval and topped with a cement-bentonite grout backfill.

Borehole 8-2 was drilled to 75 ft (22.7 m) depth near the toe of the landslide. The borehole revealed that the landslide deposit at this location had boulders of sandstone in a matrix of sand, silt, and clay within the top 20 ft (6.1 m). Below 20 ft (6.1 m) depth, the landslide deposit was found to be moist, dark brown, silty to clayey gravel and cobbles, classified by UDOT as clayey gravel to silty gravel (GC to GM). At 30 ft (9.1 m) depth, rounded to subrounded gravel and cobbles were found in a medium dense matrix of sand and silt. This material was interpreted to be stream alluvium. No shear zones within the colluvial soil or stream alluvium were encountered during drilling. The water table was found at 37 ft (11.2 m) below the surface. A 2.75 inch (7 cm) diameter Geokon inclinometer casing was placed in the borehole to a depth of 74.5 ft (22.6 m) and a sand slurry backfill was poured from 74.5 ft (22.6 m) to 35 ft (10.6 m) depth interval and topped with a cement-bentonite grout backfill.

Borehole 7-5 was drilled a half mile (0.8 km) west of the Cedar City landslide to a depth of 100.2 ft (30.4 m). The top 62 ft (18.8 m) consisted of gravel, cobbles, and boulders in a loose matrix of grey sand and silt. The bedrock below this depth was a light grey to light brown, poorly cemented, severely weathered sandstone with closely spaced

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discontinuities, interpreted to be the Tropic Shale and Dakota Formation undivided (Ktd).

A 2.75 inch (7 cm) diameter Geokon inclinometer casing was placed in the borehole to

100 ft (33 m) depth and grouted like the other two boreholes.

The geophysical survey, conducted by AMEC, showed a depth to the bedrock ranging from 71 ft (21.6 m) near the toe of the slide to 121 ft (36.9 m) near the crest of the landslide. A comparison of borehole logs and geophysical survey data shows that the bedrock in the head scarp area was found at a greater depth in the borehole logs than in the geophysical survey.

The inclinometer data did not show any evidence of movement, indicating that the landslide mass did not move during the period of monitoring (12/28/2011 – 3/21/2012).

Therefore, the inclinometer data could not be used to determine the location of the failure plane. Figure 3.5 shows an example of the inclinometer data from borehole 8-2.

3.4 Engineering Properties of Colluvial Soil and Bedrock Units

3.4.1 Grain Size Distribution

Figure 3.6 shows the results of sieve analysis for the colluvial soil. More than

50% of the colluvial soil passes through the #4 sieve and is retained on #200 sieve, indicating a sandy material. The percentage of material passing through the #200 sieve is between 4% - 6.2%. The coefficient of uniformity (Cu) is 9.1 and the coefficient of curvature (Cc) is 0.6. These results indicate that, according to the Unified Soil

33

Figure 3.5: Cumulative displacement from the inclinometer data obtained from borehole 8-2 (UDOT, 2012).

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100 D10 = 0.12 90 D30 = 0.24 D = 0.96 80 60 Cu= 8 70 Cc= 0.55

60

50

% Passing % 40

30

20

10

0 10.00 1.00 0.10 0.01 Grain Size (mm)

Figure 3.6: Grain Size Distribution curve for sample 4 of the colluvial soil.

Table 3.1: Atterberg limit data for the colluvial soil.

Plasticity Liquid Limit Plastic Limit Index Test 1 27.6 18.5 9.1 Test 2 27.8 13.0 14.8 Test 3 27.2 16.7 10.5 Mean 27.5 16.1 11.4

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Classification System (USCS), the colluvial soil is poorly graded sand (Holtz et al.,

2011).

3.4.2 Natural Water Content and Bulk Density

The natural water content of the colluvial soil ranges from 7.6% to 11.6%, with an average of 9.3%. The bulk density of the soil, as determined from the blow count values

(average ~12) obtained during drilling, is 110 pcf (1.8 Mg/m3).

3.4.3 Atterberg Limits

Table 3.1 and Figure 3.7 show the Atterberg limits test results for the material passing #200 sieve. The liquid limit ranges from 27.2 to 27.8 with a mean of 27.5; the plastic limit ranges from 13.0 to 18.5, with a mean of 16.1; and the plasticity index ranges from 8.7 to 14.8, with a mean of 11.4. Figure 3.8 shows that the fine-grained portion of the colluvial soil can be classified as clay of low plasticity (CL). Based on the combined results of sieve analysis and Atterberg limits test, and using the USCS, the colluvial soil can be classified as poorly graded sand to clayey sand (SP-SC).

3.4.4 Dry Density, Absorption, Slake Durability, and Unconfined Compressive Strength for Bedrock Units

Table 3.2 lists the dry density, absorption, slake durability index, unconfined compressive strength data for the bedrock units. For the Straight Cliffs Sandstone, the dry

Casagrande Plasticity Chart 80

70

60

50 CH

40

30 CL

Plasticity Plasticity Index OH or MH 20

10 CL-ML ML ML or OL 0 0 10 20 30 40 50 60 70 80 90 100 Liquid Limit

Figure 3.7: A plot of Atterberg limits on Casagrande’s plasticity chart showing that the fines are classified as low plasticity clay.

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Table 3.2: Summary of dry density, absorption, slake durability, and unconfined compressive strength data for the bedrock units involved in the Cedar City landslide.

Slake Durability Index Unconfined Compressive Density (pcf) Absorption (%) (Id2) Strength (psi) St. St. St. St. Max Min Mean Max Min Mean Max Min Mean Max Min Mean Dev. Dev. Dev. Dev. Straight Cliffs 187.2 134.2 159.1 26.7 8.9 7.7 8.4 0.6 n/a n/a n/a n/a 4350.0 3045.0 3465.5 513.6 Sandstone Tropic Shale 165.6 162.2 163.4 1.9 n/a n/a n/a n/a 89.8 15.6 51.5 37.1 n/a n/a n/a n/a Dakota 165.4 139.8 156.2 10.7 7.5 6.7 7.2 0.4 27.0 28.0 27.5 0.5 5480.4 3432.6 4397.4 889.2 Sandstone

Table 3.3: Two-cycle slake durability classification (ISRM, 1979).

Slake Durability Classification (Id2) 0 - 30 Very Low 30 - 60 Low 60 - 85 Medium 85 - 95 Medium-High 95 - 98 High 98 - 100 Very High

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density values range from 134.2 pounds per cubic foot (pcf) to 187.2 pcf (2.2 Mg/m3 to 3

Mg/m3), with an average density of 159.1 pcf (2.55 Mg/m3). For the Tropic Shale, the dry density ranges from 162.2 pcf to 165.6 pcf (2.6 Mg/m3 to 2.65 Mg/m3), with an average of 163.4 pcf (2.62 Mg/m3). The dry density of the Dakota Sandstone ranges from

139.8 pcf to 165.4 pcf (2.24 Mg/m3 to 2.65 Mg/m3), with an average of 156.2 pcf (2.5

Mg/m3). The absorption values range from 7.7% to 8.9%, with a mean of 8.4% for the

Straight Cliffs Sandstone, and from 6.7% to 7.5%, with a mean of 7.2%, for the Dakota

Sandstone.

In Cedar Canyon, the Tropic Shale and Dakota Sandstone are considered to be the same unit (Biek et al., 2011), therefore, the slake durability index was found for both the

Tropic Shale and the Dakota Sandstone. The Tropic Shale shows a large variation in the two-cycle slake durability index (15.6% to 89.6%), which can be attributed to its non- uniform nature. According to ASTM classification (ASTM, 1996) the slaked material is classified as type I (consists of large pieces, virtually unchanged) to type II (slaked material consists of large and small pieces). Using the ISRM two-cycle slake durability classification (Table 3.4), the durability of the Tropic Shale ranges from very low to a medium-high. The Dakota Sandstone became very rounded after two cycles slake durability test and has a two-cycle slake durability index of 27.0% to 28.0%. The slaked material from Dakota Sandstone is classified as type I to type II material. Using the

ISRM two-cycle slake durability classification (Table 3.4), the Dakota Sandstone is considered to have a very low durability. The relatively low durability of Tropic Shale and Dakota Sandstone formations explains the thick accumulation of colluvial soil at the

39

landslide site with frequent rockfalls contributing to the variable size boulders embedded in it.

The unconfined compressive strength values range from 3,045 psi to 4,350 psi (21

MPa to 30 MPa) with a mean of 3465.5 psi (24 MPa) for the Straight Cliffs Sandstone and 3432.6 psi to 5480.4 psi (23.7 MPa to 37.8 MPa) with a mean of 4397.4 psi (30.3

MPa), for the Dakota Sandstone. According to the Deere and Miller (1966) classification, shown in Table 3.5, the Straight Cliffs Sandstone belongs to Class E, or very low strength and Dakota Sandstone belongs to Class D, or low strength. The strength values determined for the Straight Cliffs Sandstone, a cliff forming unit, are lower than expected, which may be due to the use of Schmidt hammer (an empirical method) or due to experimental error. However, the low density values of this sandstone do explain, to some extent, the low strength values, as density is linearly related to unconfined compressive strength (Shakoor and Bonelli, 1991). Similarly, the low slake durability index values for the Dakota Sandstone corroborates the relatively low strength values for this sandstone. Petrographic characteristics of the sandstones were not evaluated in this study but could explain why these sandstones have lower than expected values of compressive strength. The low strength values of the Straight Cliffs and Dakota sandstones, the former forming the head scarp of the landslide and the latter comprising the bedrock underlying the colluvial soil mass, suggest that both sandstones, along with the Tropic Shale, contributed to the accumulation of the thick mass of colluvial soil.

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3.4.5 Shear Strength Parameters

The results of the direct shear test are presented in Table 3.6. The shear strength parameters determined in this study indicate that the dry soil has a higher resistance to shearing through the soil and along the soil-bedrock contact compared to wet soil. When the soil is at its natural water content, it exhibits lower strength parameters for a shear within the soil itself and along the soil-bedrock contact.

Table 3.4: Engineering classification of intact rock (Deere and Miller, 1966).

Class Description Uniaxial compressive strength (psi) A Very High Strength Over 32,000 B High Strength 16,000 - 32,000 C Medium Strength 8,000 - 16,000 D Low Strength 4,000 - 8,000 E Very Low Strength Less than 4,000

Table 3.5: Summary of the shear strength parameters for the colluvial soil and the soil-bedrock contact.

Peak Friction Angle (°) Residual Friction Angle (°) Peak Cohesion (psi) Residual Cohesion (psi)

St. St. St. St. Max Min Mean Max Min Mean Max Min Mean Max Min Mean Dev. Dev. Dev. Dev. Dry Soil 46 36 40 5.5 44 34 38 5.3 2.3 0 1.4 1.3 1 0 0.6 0.5 Soil at Natural Water 39 36 37 1.5 n/a n/a n/a n/a 1.8 0.5 1 0.7 n/a n/a n/a n/a Content Dry Soil-Dakota 47 36 42 5.5 36 33 34 1.8 1.7 0 1.1 0.9 0 0 0 0 Sandstone Contact Soil at Natural Water Content-Dakota 37 33 35 1.8 35 33 34 1 1.5 0.5 1.2 0.6 0.7 0 0.5 0.4 Sandstone Contact Dry Soil-Tropic Shale 33 25 30 4.4 25 22 24 2.1 2.3 0.6 1.4 0.8 2.15 1.25 *1.7 0.6 Contact

* Note: The residual cohesion value should not exceed the peak cohesion value. In this case, the residual value being higher than the peak value can be attributed to experimental error.

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CHAPTER 4

STABILITY ANALYSIS OF THE CEDAR CITY LANDSLIDE

4.1 Landslide Type and Failure Plane Location Used for Stability Analysis

During the subsurface investigations, discussed in Chapter 3, no shear zones were encountered within the soil itself or within the bedrock. However, in borehole 8-1, the contact between the soil and bedrock was found to be very soft to soft shale and siltstone belonging to the undivided Tropic Shale and Dakota Sandstone (see borehole logs in

Appendix B). Therefore, it can be inferred that the failure occurred along the soil-bedrock contact or slightly within the weak bedrock along this contact. The Cedar City landslide is a combination of rotational and translational movement, with the majority of the movement being translational in nature and occurring along the contact between the colluvial soil and the underlying Tropic Shale and Dakota Sandstone, undivided. The landslide started as a rotational failure along the Straight Cliffs Sandstone (head scarp), and turned into a translational failure as it moved downslope along the soil-bedrock contact. The observation that the failure occurred along the soil-bedrock contact is supported by the lower shear strength along the contact than within the soil or within the bedrock, as indicated by the direct shear test results discussed in Chapter 3.

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The stability analysis was performed with respect to three extreme groundwater conditions: dry conditions, fully saturated conditions, and varying positions of the groundwater table.

4.2 Input Parameters for Stability Analysis

The cross-section of the slide used for stability analysis is shown in Figure 4.1. It was created using a 2002 topographic map, a geologic map of the area, field observations, borehole logs, and the geophysical survey. The contact between the Straight

Cliffs Sandstone and the Tropic Shale/Dakota Sandstone is assumed to be horizontal and straight in the cross-section due to the very gentle dip of the bedding (4°), although the natural contact may be irregular and slightly inclined. The soil-bedrock parameters used for the stability analysis were the average shear strength parameters for the Tropic Shale and Dakota Sandstone separately and the average of the combined soil-bedrock parameters, provided in Table 4.1. The bedrock parameters used in the analysis were chosen in accordance with the Generalized Hoek and Brown criterion and included average unit weight, mean unconfined compressive strength, and assigned Geologic

Strength Index (GSI) values. The bedrock parameters used were 159.1 pcf (2.6 Mg/m3) and 156.2 pcf (2.5 Mg/m3) for unit weight, 3,625 psi (25 MPa) and 2,231.5 psi (16 MPa) for unconfined compressive strength, and 53 and 20 for GSI values for the Straight Cliffs

Sandstone and the undivided Tropic Shale and Dakota Sandstone, respectively. Figure

4.2 shows the chart used to determine the geological strength index for the bedrock.

Figure 4.1: Cross-section created for stability analysis (Rocscience, 2003).

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Table 4.1: Parameters used for stability analysis scenarios.

Dry Density Saturated Friction Angle (°) Cohesion (psi) (pcf) Density (pcf) Soil-Tropic 24 1.7 102.5 126.7 Shale Soil-Dakota 34 0 102.5 126.7 Sandstone Soil-Bedrock 29 0.68 102.5 126.7 Average

Figure 4.2: Geological Strength Index (GSI) chart (Marinos and Hoek, 2000).

4

7

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4.3 Stability Analysis Using the SLIDE Software Program

The SLIDE software program (Rocscience, 2003) was used to perform the stability analysis, considering a non-circular failure surface along the soil-bedrock contact. The analysis was performed with respect to three groundwater conditions: (1) completely dry slope, (2) completely saturated slope, and (3) intermediate situations with varying positions of the groundwater table. The SLIDE software program uses two methods of analysis: the Bishop Simplified Method and the Janbu Simplified Method.

For the completely dry condition, the factor of safety was found to be 1.2 for failure along the colluvial soil-Dakota Sandstone contact, 0.8 for the colluvial soil-Tropic Shale contact, and 1.02 for the average soil-bedrock parameters (Figures 4.3-4.5) for both the

Bishop Simplified and Janbu Simplified methods. The factor of safety for the completely saturated condition was 0.3 for the colluvial soil-Tropic Shale contact and 0.4 for both the colluvial soil-Dakota Sandstone and the average soil-bedrock parameters (Figures 4.6 and

4.7) for both the Bishop Simplified and Janbu Simplified methods.

For the first step in sensitivity analysis, I used varying density values between the dry density of 102.5 pcf (1.6 Mg/m3) and saturated density of 126.7 pcf (2.0 Mg/m3) to check if variation of density, associated with rainfall infiltration, alone will reduce the factor of safety to 1.0 or less. The results, included in Appendix D, showed that density variation had no effect on the factor of safety value. Therefore, as the next step, I conducted the sensitivity analysis to investigate the influence of varying positions of the water table, above the soil-bedrock contact, on the factor of safety. Sensitivity analysis was performed by adjusting the water table height to create partially saturated

4

7

Figure 4.3: Stability analysis based on dry colluvial soil-Tropic Shale strength parameters, using both Bishop and the Janbu

Simplified methods (Rocscience, 2003). 4

7

Figure 4.4: Stability analysis based on dry colluvial soil-Dakota Sandstone strength parameters, using both Bishop and the Janbu Simplified methods (Rocscience, 2003).

4

8

Figure 4.5: Stability analysis based on the averaged dry colluvial soil-bedrock strength parameters, using the Bishop Simplified method (Rocscience, 2003).

49

Figure 4.6: Stability analysis for fully saturated colluvial soil-Tropic Shale parameters, using both Bishop and the Janbu

Simplified methods (Rocscience, 2003). 50

Figure 4.7: Stability analysis for fully saturated colluvial soil-Dakota Sandstone and the average soil-bedrock parameters, using both Bishop and the Janbu Simplified methods (Rocscience, 2003).

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soil and determining the friction angle needed for a safety factor of one, while keeping cohesion at the same value (0.68 psi/4.7 kPa) (Figures 4.8–4.11). Figure 4.12 shows the friction angle required for limiting conditions (F.S. = 1) for varying positions of the water table. When the average strength parameters were used, the factor of safety decreased from 1.02 to 1.00 (failure conditions) with the water table height at 3.3 ft (1 m).

However, the water table height needed to cause failure may be less than 3.3 ft (1 m) depending on the bedrock geology controlling the failure. For example, the factor of safety for dry soil-Tropic Shale contact is 0.8, so no water is needed to induce failure.

Thus, the water table rise required to induce failure will depend on the proportion of

Tropic Shale versus Dakota Sandstone along the failure surface. No permeability tests were performed in this study, but based on the loose nature of the colluvial soil, as indicated by the blow counts, the water table build up from the bedrock is very likely to occur after heavy rain storms.

The final step in the above-described stability analysis was to evaluate the effect of water that was encountered in borehole 8-2 in the toe area of the slide. Figure 4.13 shows the geologic cross-section used for stability analysis with the level of water found in borehole 8-2. It should be noted that the cross-section in Figure 4.13 represents the pre-slide conditions whereas drilling was done from the top of the failed mass of soil after the landslide had occurred. One possible explanation for the presence of water in the toe area is the disruption of drainage within the failed soil mass whereby any water in the colluvial soil tended to accumulate within the toe area. In that case, the water found in the toe area would not have any effect on the stability of the original slope. The second

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Figure 4.8: Stability analysis with the maximum water table height at 3.3 ft (1 m) above the contact, Φrequired = 29°

(Rocscience, 2003). 53

Figure 4.9: Stability analysis with the maximum water table height at 11.7 ft (3.5 m) above the contact, Φrequired = 30° (Rocscience, 2003).

54

Figure 4.10: Stability analysis with the maximum water table height at 23.7 ft (7.2 m) above the contact, Φrequired = 32°

(Rocscience, 2003). 55

Figure 4.11: Stability analysis with the maximum water table height at 39.4 ft (11.9 m) above the contact, Φrequired = 34°

(Rocscience, 2003). 56

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45

40

35

30

25

20

15

10 Water Table Height (ft) Height Table Water 5

0 28 29 30 31 32 33 34 35 Friction Angle (°)

Figure 4.12: Variation of back-calculated friction angle for varying heights of water table, for a safety factor of one. Note: 3.3 feet = 1 m.

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Figure 4.13: Geologic cross-section used for stability analysis showing the level of water encountered in Borehole 8-2. Note that the cross-section represents pre-slide conditions. After the failure, the toe area was buried under landslide debris.

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possibility is that the water represents the actual water table. Even in this case, the effect of water on the stability of the original slope would be negligible because the associated pore pressure would have acted on a very small portion (<10%) compared to the total length of the failure surface.

4.4 Causes of Landslide

Cedar City is located in an arid region, with very few precipitation events, as can be seen in Figure 4.14. Colluvial soils formed in arid regions often exhibit loose soil structure that is stable only as long as it remains dry (Turner, 1996). The loose nature of the colluvial soil at the Cedar City landslide is corroborated by its relatively low blow count value (N = 12) and dry density (100 pcf/1.6 Mg/m3). The precipitation of 2.13 inches (5.4 cm) on October 6, 2011 as well as the total precipitation of 2.68 inches (6.8 cm) for October 2011 exceeded the mean precipitation of 1.58 inches (4.0 cm) for the month of October from 1981 to 2010. With limited vegetation, the water percolated through the colluvial soil and created partially saturated conditions.

The remnants of the 2009 rockfall remained on slope after remediation, adding to the weight of the colluvial soil. A slope angle of ~30° was steep enough to contribute to the driving force in addition to other factors. The undercutting of the slope toe by the

Coal Creek also appears to have contributed to the landslide initiation.

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2.5 October 6, 2011

2011 Precipitation Monthly Mean (1981-2010)

2.0

1.5

1.0 Precipitation (in) Precipitation

0.5

0.0 1-Sep 11-Sep 21-Sep 1-Oct 11-Oct 21-Oct 31-Oct

Figure 4.14: Daily precipitation outside Cedar City, UT from September 1st to October 31st, 2011.

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CHAPTER 5

REMEDIAL MEASURES

UDOT used a combination of remediation methods to stabilize Cedar City landslide and repair SR 14. The three categories of commonly used slope stabilization methods are: 1) reinforcement (tied-back retaining walls, rock bolts/anchors, dowels, shotcrete, buttresses), 2) rock removal (regrading, scaling, trimming), and 3) protection measures (drainage, ditches, wire-mesh nets, barriers/catch fences) (Wyllie and Mah,

2004). Below is a list of the remediation measures used at the Cedar City landslide site:

1. Landslide material was cleared away from the road using bulldozers. The slope

above the road (south side) was re-graded to 2H:1V (original slope varied, 2H:1V

or steeper) (Figure 5.1) and the slope below the road (north side) was re-graded to

2H:1V where the slide occurred and 1.75H:1V on the slope west of the landslide

(original slope varied, 2H:1V or steeper).

2. Straight Cliffs Sandstone, in the head scarp area, was scaled to reduce the

potential for future rockfalls (Figure 5.2).

3. A riprap filled cut ditch was placed upslope of the road to collect surface runoff

and any groundwater seeping from the toe of the slope above the road. The ditch

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Figure 5.1: Re-graded slope above the road and riprap-filled drainage ditch.

Figure 5.2: Scaling of the Straight Cliffs Sandstone in the head scarp area.

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is approximately 11 ft (3.3 m) wide, 2 ft (0.6 m) deep, and lined with a 1 ft (0.3

m) thick riprap.

4. Six 24 inch (61 cm) diameter culverts, surrounded by filter fabric, were placed

beneath the SR 14 to divert drainage from the ditch to the other side of SR 14. At

the end of each culvert, riprap was used on the downslope side of SR 14 to allow

water from the culverts run into Coal Creek and to relieve any internal drainage.

5. A modular block retaining wall was built on the east side of the landslide area due

to the narrowing valley (Figures 5.3 and 5.4). A modular block retaining wall is

created by smaller blocks of concrete that lock together. This is more suitable for

a narrow valley because it requires less excavation to build and can be flexible to

curve around irregular areas. The retaining wall is used to give support to the

colluvial soil under SR 14 where the valley narrows. The blocks were laid on top

of a 6 inch (15.3 cm) thick concrete leveling pad, that was poured in place, a

minimum of 2 ft (0.6 m) below the surface of the colluvial soil along the front

face of the retaining wall. Culverts were placed behind the wall to provide

drainage from behind the wall and under the road.

6. Concrete barriers were placed along the road to stop any debris from falling into

the roadway.

7. The subgrade material below the road was compacted using a smooth roller

(Figure 5.5). Figure 5.6 shows a view from the slope above the road, looking

down at SR 14. State Route 14 was open for daytime traffic by end of May 2012

(Figure 5.7), and completely finished on September 26, 2012 (Figure 5.8).

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Figure 5.3: East side view of the modular block retaining wall. The white pipe carries water to the culvert.

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Figure 5.4: West side view of the modular block retaining wall.

Figure 5.5: Smooth wheel roller compacting subgrade material for reconstruction of SR 14.

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Figure 5.6: View of the riprap filled ditch and road from slope above.

Figure 5.7: Aerial view of the repaired landslide and SR 14 (UDOT, 2012).

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Figure 5.8: Riprap filled drainage ditch and the newly paved SR 14 (UDOT, 2012).

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8. Eight species of vegetation were planted on the slope, in a mix of approximately

281 live seeds per square foot (0.09 m2), after completing the repairs to SR 14.

In order to check the degree of stability of remediated slope, the tangent of the angle of friction was divided by the tangent of the re-graded slope angle. This conservative approach ignored any contribution of cohesion and the retaining wall. This approach results in a factor of safety of 1.1 for the average friction angle between colluvial soil and bedrock and 1.3 for the friction angle between colluvial soil-Dakota

Sandstone contact. These factors of safety values are still marginal if buildup of pore pressure occurs. However, considering that enough drainage has been provided and a retaining wall has been constructed, it is anticipated that the re-graded slope will be stable under normal conditions.

The remediation that UDOT implemented to repair SR 14 considered many potential future issues. The slope inclinometers were left in place to continue to monitor movement within the slope. The methods for allowing drainage to pass under the newly constructed road will help prevent pore-water pressure buildup within the colluvial soil.

The retaining wall is an appropriate way to provide support to the road and prevent further movement in that area of the Cedar Canyon. A temporary berm was used along the toe of the slope, near Coal Creek, for temporary erosion control. A permanent structure to prevent erosion of the toe of the slope would be a better way to prevent future slope movement. There are still many overhangs above SR 14, in the Straight Cliffs

Sandstone, that could lead to potential falls and future damage to the road. No

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preventative measures were used (rock bolts, catch fences, steel wire mesh) to protect SR

14 from future problems. Since Cedar Canyon has a history of rockfalls, preventative measures would save the state money in future repairs.

CHAPTER 6

AN OVERVIEW OF SLOPE MOVEMENT HAZARDS IN THE CEDAR CANYON

A reconnaissance survey of the Cedar Canyon shows that, besides the Cedar City landslide area discussed previously, there are many other places in the canyon that exhibit a high potential for slope movement and the associated hazard. Although a quantitative assessment of the hazard associated with slope movements was beyond the scope of this study, numerous pictures were taken to show the potential for slope movement and the associated hazard. Figures 6.1 to 6.5 show the hazardous areas of the canyon along SR

14. On December 10, 2012, a major rockfall impacted SR 14 around mile marker 7.5.

The road was damaged at several places and the concrete barriers were damaged and moved, with most of the debris ending up in the drainage ditch. Figures 6.6 to 6.8 show the rockfall source area and damage to the road.

In addition to the reconnaissance survey, a kinematic analysis was performed on the discontinuities measured in the vicinity of the Cedar City landslide, using the

RockPack III software (Watts et al., 2003). The purpose of this analysis was to show the potential for different types of slope movement in the Cedar Canyon. The results of kinematic analysis, included in Appendix D, show that there is potential for wedge and toppling failures. Figure 6.9 shows the kinematic analysis results for the discontinuities

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71

Figure 6.1: Unfavorably oriented joints within the Straight Cliffs Sandstone in the Cedar Canyon showing the potential for a variety of slope movements (rockfalls, plane failures, wedge failures, toppling failures).

72

Figure 6.2: Jointed nature of the Straight Cliffs Sandstone, resulting in a blocky nature of the rock mass and a potential for rockfalls and other types of slope movement.

73

Figure 6.3: Potential for rockfall hazard along discontinuities in the Straight Cliffs Sandstone.

74

Figure 6.4: Valley stress relief joints along the Cedar Canyon wall showing the potential for rockfalls and plane failures. Any slope movement at this site can be hazardous to SR 14, as seen in the picture. Notice the catchment ditch is very narrow considering the slope height.

75

Figure 6.5: Debris from previous rockfalls in the canyon.

76

Figure 6.6: Source area for the 2012 rockfall above SR 14 (Lund, 2012).

Figure 6.7: Rockfall debris on SR 14 (Lund, 2012). The hazard to traffic is obvious.

77

Figure 6.8: Damage to SR 14 from 2012 rockfall (Lund, 2012).

Figure 6.9: Kinematic analysis using the RockPack III software, based on measured discontinuities within the Straight Cliffs Sandstone (Watts et al, 2003). The intersection of joint set 1 and the valley stress relief joints indicates potential for wedge failures. The intersection of joint sets 1 and 2 shows potential for toppling failures. If the dip of the relief joints is gentler than

7

the slope face, there is potential for plane failure. 8

79

measured within the Straight Cliffs Sandstone. The results of kinematic analysis clearly show that in addition to landslides involving colluvial soil, such as the Cedar City landslide, there is a great potential for a variety of slope movements (rockfalls, wedge failures, plane failures, and toppling failures) occurring along the discontinuities in the rocks comprising the Cedar Canyon walls. The intersection of joint set 1 and the valley stress relief joints shows potential for wedge failures. The intersection of joint set 1 and 2 shows potential for toppling failures. If the dip of the relief joints is gentler than the slope face at a given location, there is potential for plane failure. Since SR 14 is located adjacent to the walls, these slope movements pose a serious threat to the safety of the traffic along this road.

I would recommend that a hazard assessment should be performed throughout the entire Cedar Canyon based on Utah Rockfall Hazard Rating System. At the critical sites indicated by the hazard assessment, a detailed evaluation of the hazard potential should be carried out, based on discontinuity measurements, kinematic analysis, and rockfall trajectories as indicated by CRSP or Rocfall software programs. With an evaluation of critical sites, measures can be taken to prevent future hazards within the Cedar Canyon.

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CHAPTER 7

CONCLUSIONS

Based on the results of this research, the following conclusions can be drawn:

1. The Cedar City landslide is a combination of rotational and translational

movement, with majority of the movement occurring along the contact between

the colluvial soil and the underlying Tropic Shale and Dakota Sandstone - the

undivided bedrock. The rotational movement is confined to the head scarp area.

2. The causes of the Cedar City landslide include a relatively steep colluvial soil

slope of ~30°, extra weight on the soil from previous rockfalls, overlapping

historical landslide deposits, and buildup of pore pressure due to a rainstorm prior

to failure.

3. The stability analysis, using the SLIDE software program, indicates a factor of

safety of 0.8 to 1.2 for the dry conditions and 0.3 to 0.4 for the fully saturated

conditions. Back-calculation analysis indicates that for an average friction angle

of 29°, a 3.3 ft (1 m) rise of the water table above the soil-bedrock contact is

required to cause the failure; however, it may be less than that if the majority of

the bedrock along the failure surface consisted of Tropic Shale.

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4. Remedial measures used by UDOT to stabilize and repair SR14 include re-

grading the slope of the failed colluvial soil to 2H:1V, placing a riprap-filled ditch

along the road for drainage purposes, installing a retaining wall below the road on

the east side of the landslide, recompacting the subgrade material under the road

and reconstructing the pavement.

82

REFERENCES

American Society for Testing and Materials, 1996, Soil and Rock; Dimension Stone Geosynthetics: Annual Book of ASTM Standards, Section 08, Conshocton, Pa, 668 p

Biek, R.F., Maldonado, F., Moore, D.W., Anderson, J.J., Rowley, P.D., Williams, V.S., Nealey, L.D., and Sable, E.G., 2011, Interim Geologic Map of the West Part of the Panguitch 30'x60' Quadrangle, Garfield, Iron, and Kane Counties, Utah, Unpublished.

Brabb, E.E., 1989, Landslides: Extent and economic significance in the United States, in Brabb, E.E. & Harrod, B.L., editors, Landslides: Extent and Economic Significance: Proceedings of the 28th International Geological Congress, Symposium on Landslides, Washington D.C., July, 1989: A.A. Balkema, Rotterdam, pp. 25-50.

Cruden D.M., and Varnes, D.J., 1996, Landslide Types and Processes: Landslide: investigation and mitigation: Transportation Research Board, Special Report 247, ch. 3, pp. 36-71.

Deere, D.U. and Miller, R.P., 1966, Engineering classification and index properties for intact rock: Tech. Rep. No. AWFL-TR-65-116, Univ. of Illinois, Urbana, pp. 167.

Erskine, M.C., Faulds, J.E., Bartley, J.M. and Rowley, P.D., 2001, The Geologic Transition, High Plateaus to the Great Basin – A Symposium and Field Guide: The Mackin Volume. Utah Geological Association, publication 30, pp. 345.

Giraud, R.E. and Lund, W.R., 2005, The June 3, 2005, Black Mountain Debris Flow, Iron County, Utah. Utah Geological Survey Technical Report, pp. 1.

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Gregory, H.E., 1950, Geology of eastern Iron County, Utah. Utah Geological and Mineralogical Survey, Bulletin 37, pp. 45-50.

Harty, K., 1989, The Cedar Canyon Landslide. Utah Geological Survey: Survey Notes, v. 23, no. 2, pp. 14.

Harty, K., 1991, Landslide Map of Utah. Utah Geological and Mineral Survey, Map 133, pp. 13.

Holtz, R.D., Kovacs, W.D., and Sheahan, T.C., 2011, An Introduction to Geotechnical Engineering, 2nd Edition. Prentice Hall, New Jersey. 775 p.

ISRM, 1979, Suggested methods for determining water content, porosity, density, absorption, and related properties and swelling and slake durability index properties. Intl. Soc. Rock Mech. Comm. On Standardization of Laboratory and Field Tests, Intl. J. Rock Mech. Min. Sci. & Geomech. Abstr., Vol. 22, pp. 141- 156.

Lund, W.R, Knudsen, T.R., and Brown, K.E., 2009, Large Rock Fall Closes Highway near Cedar City, Utah. Utah Geological Survey: Survey Notes, v. 41, no. 3, pp. 8- 9.

Lund, W.R, Knudsen, T.R., and Fadling, D., 2011, Another Large Landslide Closes Highway near Cedar City, Utah. AEG News, v. 54, no. 4, pp. 24-25.

Marinos, P. and Hoek, E., 2000, GSI: A geologically friendly tool for rock mass strength estimation. GEOENG 2000, Melbourne, Australia. Lancaster, PA: Technomic Publishers, pp. 1422–1446.

Park, H.J. and West, T.R., 2002, Sampling bias of discontinuty orientation caused by linear sampling technique: Engineering Geology, Vol. 66, pp. 99-110.

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Parowan Times. November 24, 1915, Newsy notes from Cedar City, pg. 2. Retrieved from http://digitalnewspapers.sandbox.lib.utah.edu.

Piteau, D.R. and Martin, D.C., 1977, Field Manual: Description of the detail line engineering geology mapping method.

RocScience, 2003, Determining input parameters for rocfall analysis, Rocfall News.

Shakoor, A., and Barefield, E. H., 2009, Relationship between unconfined compressive strength and degree of saturation for selected sandstones. Environmental & Engineering Geoscience, v. 15, no. 1, pp. 29-40.

Shakoor, A., and Bonelli, R. E. 1991, Relationship between petrographic characteristics, engineering index properties and mechanical properties of selected sandstones. Bull Assoc Eng Geol, v. 28, no. 1, pp. 55-71.

Turner, A.K. 1996, Colluvium and Talus. Landslide: investigation and mitigation, Transportation Research Board, Special Report 247, ch. 20, pp. 525-549.

Watts, C. F., Gilliam, D., Hrovatic, M., and Hong, H., 2003, User’s manual-ROCKPACK III for windows. Rock Slope Stability Computerized Analysis Package, Part One- Stereonet Analyses, CF Watts & Associates.

Wyllie, D.C. and Mah, C.W., 2004. Rock Slope Engineering, 4th Edition. Spon Press, New York, 431 p.

APPENDIX A

DISCONTINUITY DATA

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Table A-1: Dakota Sandstone Discontinuities

Note: 1 inch = 2.54 cm

Spacing Dip (°) Dip Direction (°) Type 3" 82 316 Joint 9" 81 275 Joint 1'10" 80 359 Joint 1'11" 89 099 Joint 2'9" 90 104 Joint parallel 84 315 Joint 9'1" 83 140 Joint parallel 86 186 Joint 11'9" 90 130 Joint 11'11" 86 142 Joint 12'9" 90 144 Joint 12'9" 90 157 Joint 15'4" 81 072 Joint 13'6" 80 272 Joint 18'6" 88 147 Joint 19'3" 90 148 Joint 19'6" 86 149 Joint 21'3" 89 207 Joint 21'7" 76 277 Joint 22'2" 89 315 Joint 22'4" 87 151 Joint 22'4" 90 154 Joint 22'9" 90 092 Joint 22'8" 90 095 Joint 23'4" 90 153 Joint 23'10" 73 161 Joint 24'1" 70 249 Joint 24'5" 90 106 Joint 24'7" 90 152 Joint 25'3" 85 155 Joint 25'8" 80 145 Joint 26' 90 114 Joint

87

Dip (°) Dip Direction (°) Type Dip (°) Dip Direction (°) Type 1 035 Bedding 76 262 Joint 2 033 Bedding 80 042 Joint 10 022 Bedding 86 025 Joint 5 215 Bedding 90 090 Joint 5 228 Bedding 76 251 Joint 4 217 Bedding 90 228 Joint 6 043 Bedding 86 320 Joint 2 223 Bedding 89 253 Joint 2 225 Bedding 75 328 Joint 1 033 Bedding 80 043 Joint 14 213 Bedding 85 136 Joint 13 219 Bedding 90 154 Joint 4 216 Bedding 80 209 Joint 12 034 Bedding 90 146 Joint 6 039 Bedding 88 138 Joint 9 221 Bedding 67 218 Joint 84 309 Joint 85 035 Joint 81 313 Joint 75 138 Joint 87 036 Joint 90 211 Joint 82 029 Joint 85 143 Joint 87 020 Joint 86 357 Joint 82 141 Joint 85 161 Joint 90 149 Joint 89 232 Joint 88 219 Joint 78 140 Joint 89 336 Joint 82 040 Joint 72 082 Joint 70 118 Joint 87 331 Joint 90 153 Joint

88

Table A-2: Straight Cliffs Sandstone Discontinuities

Note: 1 inch = 2.54 cm

Spacing Dip (°) Dip Direction (°) Type 1" 80 024 Joint 2" 75 284 Joint 8" 90 177 Joint 8" 90 127 Joint 9" 73 195 Joint 1'1" 85 155 Joint parallel 75 082 Joint 1'6" 64 220 Joint parallel 70 100 Joint 2' 75 215 Joint 2'9" 82 090 Joint daylight 72 130 Joint 4'10" 29 035 Joint 5'3" 86 319 Joint 13'3" 90 099 Joint 13'5" 9 147 Bedding 14' 65 176 Joint parallel 81 309 Joint 15'6" 74 232 Joint 15'6" 90 094 Joint 16'1" 67 175 Joint 16'2" 90 097 Joint 16'8" 89 138 Joint daylight 89 128 Joint 18'7" 43 037 Joint 18'9" 85 260 Joint 19'5" 74 258 Joint 19'5" 65 180 Joint 20' 65 165 Joint 20' 70 085 Joint 21'3" 66 186 Joint 22'8" 67 128 Joint

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Dip (°) Dip Direction (°) Type Dip (°) Dip Direction (°) Type 60 326 Joint 76 125 Joint 84 328 Joint 52 201 Joint 70 022 Joint 62 297 Joint 78 030 Joint 80 135 Joint 34 018 Joint 77 141 Joint 71 298 Joint 87 073 Joint 89 306 Joint 75 117 Joint 12 009 Bedding 10 140 Bedding 86 199 Joint 22 138 Joint 51 290 Joint 65 301 Joint 87 300 Joint 73 174 Joint 80 029 Joint 71 174 Joint 86 126 Joint 72 327 Joint 70 072 Joint 88 189 Joint 42 104 Joint 72 114 Joint 9 315 Bedding 42 175 Joint 87 030 Joint 90 173 Joint 75 029 Joint 88 132 Joint 80 345 Joint 72 098 Joint 10 165 Bedding 3 018 Bedding 80 258 Joint 75 307 Joint 85 296 Joint 88 180 Joint 65 331 Joint 85 150 Joint 56 035 Joint 69 194 Joint 7 158 Bedding 84 299 Joint 14 176 Bedding 32 326 Joint 0 086 Bedding 76 104 Joint 66 005 Joint 50 315 Joint 81 002 Joint 63 178 Joint 65 004 Joint 60 309 Joint 63 120 Joint 8 136 Bedding 61 348 Joint 84 260 Joint 75 322 Joint 90 163 Joint 84 227 Joint 66 115 Joint

APPENDIX B

BOREHOLE LOGS, INCLINOMETER DATA, GEOPHYSICAL SURVEY, AND RAINFALL DATA

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93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

APPENDIX C

LABORATORY DATA

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Table C-1: Natural Water Content Data

Sample Number 1 2 3 4 5 6 Plate Wt (g) 11.8 14.8 14.9 14.0 15.0 17.2 Initial Sample + Plate (g) 514.7 515.4 539.8 523.6 528.7 516.9 Initial Sample Weight (g) 502.9 500.6 524.9 509.6 513.7 499.7 Dry Sample + Plate (g) 479.3 478.9 492.9 473.3 475.2 479.5 Dry Sample (g) 467.5 464.1 478.0 459.3 460.2 462.3 Water in Sample (g) 35.4 36.5 46.9 50.3 53.5 37.4 NWC (%) 7.6 7.9 9.8 11.0 11.6 8.1 AVG NWC: 9.3

Table C-2: Grain Size Distribution Data

Sieve #4 #10 #40 #100 #200 pass #200 Total Wt Sieve Wt (g) 461.5 422.2 352.9 308.4 294.7 372.2 Sample 1 (g) 183.6 99.3 157.7 301.1 120.5 49.8 912.0 Sample 2 (g) 211.4 89.4 148.9 285.4 114.6 48.2 897.9 Sample 3 (g) 42.2 53.4 192.8 96.3 34.1 27.5 446.3 Sample 4 (g) 44.2 53.7 206.3 105.3 37.1 29.1 475.7

Table C-3: Percent Passing

Sieve Number #4 #10 #40 #100 #200 Grain Size (mm) 4.75 2.00 0.425 0.150 0.074 Sample 1 79.9 69.0 51.7 18.7 5.5 Sample 2 76.5 66.5 49.9 18.1 5.4 Sample 3 90.5 78.6 35.4 13.8 6.2 Sample 4 90.7 79.4 36.1 13.9 6.1

90

D10 = 0.10 80 D30 = 0.22

70 D60 = 0.8 Cu= 8 60 Cc= 0.61

50

40 % Passing % 30

20

10

0 10.00 1.00 0.10 0.01 Grain Size (mm)

Figure C-1: Grain Size Distribution Curve for Sample 1

1

17

90

D10 = 0.10 80 D30 = 0.23 D = 0.95 70 60 Cu= 9.5

60 Cc= 0.56

50

% Passing % 40

30

20

10

0 10.00 1.00 0.10 0.01 Grain Size (mm)

Figure C-2: Grain Size Distribution Curve for Sample 2

1

18

100

90 D10 = 0.12 D30 = 0.25 80 D60 = 1.0 70 Cu= 8.3

Cc= 0.52 60

50 % Passing % 40

30

20

10

0 10.00 1.00 0.10 0.01 Grain Size (mm)

Figure C-3: Grain Size Distribution Curve for Sample 3

1

19

100 D = 0.12 90 10 D30 = 0.24 80 D60 = 0.96 Cu= 8 70

Cc= 0.55

60

50 % Passing %

40

30

20

10

0 10.00 1.00 0.10 0.01 Grain Size (mm)

Figure C-4: Grain Size Distribution Curve for Sample 4

1

20

121

Atterberg Limits Data

Project: Cedar City Landslide Test No: 1

Sample Description: Light brown clayey silt with some sand

Liquid Limit = 27.6 Plastic Limit = 16.1 Plasticity Index = 11.43 USCS Classification = CL

Plastic Limit Data

Container 11 18 32 Wet Wt + Dish (g) 36.3 34.2 34.7 Dry Wt + Dish (g) 35.8 33.9 34.4 Water Wt (g) 0.5 0.3 0.3 Container Wt (g) 33.1 31.6 32.6 Dry Soil Wt (g) 2.7 2.3 1.8 Water Content (%) 18.5 13.0 16.7

Liquid Limit Data

Container 22 24 26 30 43 10 Number of Blows 52 29 48 36 19 9 Wet Wt + Dish (g) 70.2 71.1 56.7 64.9 52.8 51.9 Dry Wt + Dish (g) 62.8 63 51.8 58.2 48.2 47.3 Water Wt (g) 7.4 8.1 4.9 6.7 4.6 4.6 Container Wt (g) 31.8 32.1 31.9 32.4 32.2 32 Dry Soil Wt (g) 31 30.9 19.9 25.8 16 15.3 Water Content (%) 23.9 26.2 24.6 26.0 28.8 30.1

32

30 LL 28 26 24

WaterContent(%) 22 20 5 50

1

Number of Blows 12

122

Atterberg Limits Data

Project: Cedar City Landslide Test No: 2

Sample Description: Light brown clayey silt with some sand

Liquid Limit = 27.8 Plastic Limit = 16.1 Plasticity Index = 11.7 USCS Classification = CL

Liquid Limit Data

Container 20 21 22 31 43 Number of Blows 47 15 35 23 5 Wet Wt + Dish (g) 67.8 52.3 57.1 50.4 46.6 Dry Wt + Dish (g) 60.9 47.9 51.9 46.6 42.8 Water Wt (g) 6.9 4.4 5.2 3.8 3.8 Container Wt (g) 31.9 32 31.8 32.6 31.8 Dry Soil Wt (g) 29 15.9 20.1 14 11 Water Content (%) 23.8 27.7 25.9 27.1 34.5

40 38

36 34 32 30 LL 28 26

WaterContent(%) 24 22 20 3 30 Number of Blows

1

12

123

Atterberg Limits Data

Project: Cedar City Landslide Test No: 3

Sample Description: Light brown clayey silt with some sand

Liquid Limit = 27.2 Plastic Limit = 16.1 Plasticity Index = 11.1 USCS Classification = CL

Liquid Limit Data

Container 1 4 6 10 14 Number of Blows 57 14 35 29 9 Wet Wt + Dish (g) 53 46.9 58.7 50.9 53 Dry Wt + Dish (g) 49.1 43.6 53.2 46.9 48.2 Water Wt (g) 3.9 3.3 5.5 4 4.8 Container Wt (g) 32.3 31.7 32.2 32 32.1 Dry Soil Wt (g) 16.8 11.9 21 14.9 16.1 Water Content (%) 23.2 27.7 26.2 26.8 29.8

34

32

30

28

26 LL

WaterContent(%) 24

22

20 5 50 Number of Blows

1

12

124

Absorption Data

Sample Dry Wt (g) Saturated Wt (g) Submerged Wt (g) Absorption (%) S1 166.6 181.4 101.8 8.9 S2 157.4 169.5 95.3 7.7 S3 236.4 256.9 145.0 8.7 D1 153.3 164.8 92.2 7.5 D2 149.2 159.2 88.3 6.7 D3 184.5 198.1 110.3 7.4

Density Data

Sample Density (pcf) Density (Mg/m3) D1 142.90 2.29 D2 148.51 2.38 D3 139.78 2.24 D4 162.86 2.61 D5 165.36 2.65 D6 165.36 2.65 D7 161.62 2.59 D8 163.49 2.62 S1 187.20 3.00 S2 156.00 2.50 S3 134.16 2.15 T1 162.24 2.6 T2 162.24 2.6 T3 165.6 2.65

1

12

125

Slake Durability Test Data

Project: Cedar City Landslide Test No: 1

Sample Description: Dark grey shale with laminations present

Cycle Pan # Pan Wt (g) Sample + Pan Wt (g) Sample Wt (g) pre-test 1 14.7 515 500.3 1 1 14.7 197.6 182.9 2 1 14.7 92.9 78.2

Slake Durability Index Id(cycle 1):

Id1 = [(Dry Wt cycle 1)/(Dry Wt init.)]*100

Id1 = 36.6

Slake Durability Index Id(cycle 2):

Id2 = [(Dry Wt cycle 2)/(Dry Wt init.)]*100

Id2 = 15.6

ASTM Classification (Type I, II, III): II – Retained material consisting of large and small pieces

Slaked sample after 2 cycles

1

12

126

Slake Durability Test Data

Project: Cedar City Landslide Test No: 2

Sample Description: Dark grey shale and siltstone with laminations present

Cycle Pan # Pan Wt (g) Sample + Pan Wt (g) Sample Wt (g) pre-test 2 15.2 514.9 499.7 1 2 15.2 378.4 363.2 2 2 15.2 260.9 245.7

Slake Durability Index Id(cycle 1):

Id1 = [(Dry Wt cycle 1)/(Dry Wt init.)]*100

Id1 = 72.7

Slake Durability Index Id(cycle 2):

Id2 = [(Dry Wt cycle 2)/(Dry Wt init.)]*100

Id2 = 49.2

ASTM Classification (Type I, II, III): II – Retained material consisting of large and small pieces

Slaked sample after 2 cycles

1

12

127

Slake Durability Test Data

Project: Cedar City Landslide Test No: 3

Sample Description: Dark grey siltstone

Cycle Pan # Pan Wt (g) Sample + Pan Wt (g) Sample Wt (g) pre-test 3 17 566.3 549.3 1 3 17 521.1 504.1 2 3 17 510 493

Slake Durability Index Id(cycle 1):

Id1 = [(Dry Wt cycle 1)/(Dry Wt init.)]*100

Id1 = 91.8

Slake Durability Index Id(cycle 2):

Id2 = [(Dry Wt cycle 2)/(Dry Wt init.)]*100

Id2 = 89.8

ASTM Classification (Type I, II, III): I – Retained material remains virtually unchanged

Slaked sample after 2 cycles

1 12

128

Slake Durability Test Data

Project: Cedar City Landslide Test No: 4

Sample Description: Tan to beige sandstone

Cycle Pan # Pan Wt (g) Sample + Pan Wt (g) Sample Wt (g) pre-test 4 14.6 554.1 539.5 1 4 14.6 233.1 218.5 2 4 14.6 165.7 151.1

Slake Durability Index Id(cycle 1):

Id1 = [(Dry Wt cycle 1)/(Dry Wt init.)]*100

Id1 = 40.5

Slake Durability Index Id(cycle 2):

Id2 = [(Dry Wt cycle 2)/(Dry Wt init.)]*100

Id2 = 28.0

ASTM Classification (Type I, II, III): II – Retained material consisting of large and small pieces

Slaked sample after 2 cycles

1 12

129

Slake Durability Test Data

Project: Cedar City Landslide Test No: 5

Sample Description: Tan to beige sandstone

Cycle Pan # Pan Wt (g) Sample + Pan Wt (g) Sample Wt (g) pre-test 5 14 502.2 488.2 1 5 14 200.6 186.6 2 5 14 147.8 133.8

Slake Durability Index Id(cycle 1):

Id1 = [(Dry Wt cycle 1)/(Dry Wt init.)]*100

Id1 = 38.2

Slake Durability Index Id(cycle 2):

Id2 = [(Dry Wt cycle 2)/(Dry Wt init.)]*100

Id2 = 27.4

ASTM Classification (Type I, II, III): I – Retained material consisting of large pieces

Slaked material after 2 cycles

1 12

130

Slake Durability Test Data

Project: Cedar City Landslide Test No: 6

Sample Description: Tan to beige sandstone

Cycle Pan # Pan Wt (g) Sample + Pan Wt (g) Sample Wt (g) pre-test 6 15 526.2 511.2 1 6 15 180 195 2 6 15 152.9 137.9

Slake Durability Index Id(cycle 1):

Id1 = [(Dry Wt cycle 1)/(Dry Wt init.)]*100

Id1 = 38.2

Slake Durability Index Id(cycle 2):

Id2 = [(Dry Wt cycle 2)/(Dry Wt init.)]*100

Id2 = 27.0

ASTM Classification (Type I, II, III): I – Retained materials consisting of large pieces

1

Slaked sample after 2 cycles 12

131

Direct Shear Test Data

Project: Cedar City Landslide Test No: 1 Sample Description: Tan to beige dried colluvial soil

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 24.2 lbs, 50.2 lbs, 77.2 lbs Volume of Compacted Sample: 51.6 cm3

Table C-4 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 18.3 26.2 31.4 20 22.2 37.6 46.8 30 23.5 44.1 55.9 40 23.9 47.7 63.1 50 24.2 49.7 68 60 23.9 50 68.7 70 22.9 50.2 75.2 80 23.2 48.9 77.2 90 23.7 48.4 77.2 100 23.5 47.9 76.8 110 23.5 45.8 76.2 120 23.5 44.8 74.9 130 23.5 43.8 73.2 140 23.2 42.5 71.6 150 22.6 40.8 70 160 22.2 40.2 68 170 21.3 40.2 66.1 180 21.3 39.6 64.7 190 21.3 39.1 63.1 200 21 38.2 61.5 210 21 38.2 62.8 220 21 38.2 64.7 230 21.3 39.6 66.4 240 21.3 40.5 68 250 21.1 39.2 68.7 260 20.2 39.2 68.3 270 19.6 39.2 68.3 280 20 38.9 68 290 20.6 38.3 67.7 300 20.2 38.3 67.4 310 19.8 38 67.7 320 19.8 37.6 68.3 330 19.6 37.4 68 340 19.3 38.9 350 20 39.6

1

12

132

Direct Shear Test Data

Project: Cedar City Landslide Test No: 2 Sample Description: Tan to beige dried colluvial soil

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 25.3 lbs, 46.9 lbs, 59.7 lbs Volume of Compacted Sample: 51.6 cm3

Table C-5 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 14.1 23.9 32.4 20 19.3 32.7 42.2 30 21.3 38.7 47.6 40 22.9 42.5 52.3 50 23.9 44.8 55.9 60 24.7 46.1 57.6 70 25.2 46.9 58.9 80 25.3 46.8 59.2 90 25.2 46.3 59.5 100 24.2 46.4 59.7 110 23.2 45.5 59.5 120 22.6 44.0 58.4 130 21.9 42.3 57.1 140 21.3 41.0 57.2 150 20.4 39.9 56.7 160 18.0 39.2 56.6 170 19.5 38.9 55.9 180 19.6 39.2 55.1 190 19.9 39.2 54.3 200 19.9 39.2 53.0 210 20.3 38.9 52.5 220 20.6 38.6 52.0 230 20.8 38.6 52.0 240 20.9 38.4 52.0 250 20.9 38.6 52.0 260 20.9 38.7 52.2 270 21.1 38.6 52.0 280 21.1 37.6 52.2 290 21.1 37.6 52.0 300 20.9 37.6 52.0 310 20.8 36.6 52.0 320 20.8 36.0 51.8 330 20.9 36.6 51.2 340 20.6 36.8 51.2 350 20.9 37.6 53.6

1

12

133

Direct Shear Test Data

Project: Cedar City Landslide Test No: 3 Sample Description: Tan to beige dried colluvial soil

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 27.6 lbs, 47.1 lbs, 63.3 lbs Volume of Compacted Sample: 51.6 cm3

Table C-6 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 21.9 30.7 31.4 20 24.5 39.7 43.5 30 25.8 44.3 47.1 40 27.1 46.8 55.3 50 27.6 47.1 59.0 60 27.1 46.8 61.5 70 26.2 45.5 62.8 80 24.9 43.8 63.3 90 23.9 41.9 61.8 100 23.2 40.9 59.8 110 23.1 39.2 58.9 120 23.5 38.9 57.7 130 23.2 38.9 56.2 140 22.6 38.4 55.6 150 22.2 38.3 55.6 160 22.2 37.9 55.9 170 22.2 37.9 57.2 180 22.1 37.4 57.6 190 21.9 38.9 58.4 200 21.6 40.1 58.2 210 21.6 40.5 59.0 220 21.3 40.9 59.5 230 21.3 41.2 59.8 240 21.3 41.4 60.5 250 21.1 41.5 60.2 260 20.8 41.5 60.5 270 20.8 41.9 60.8 280 20.9 42.7 61.3 290 21.6 42.2 61.5 300 21.4 42.5 61.5 310 21.6 42.7 61.1 320 22.4 42.8 60.8 330 22.9 43.2 61.8 340 22.6 43.2 62.1 350 22.2 42.5 62.5

1

12

134

Direct Shear Test Data

Project: Cedar City Landslide Test No: 1 Sample Description: Tan to beige colluvial soil, at natural water content

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 24.2 lbs, 43.5 lbs, 60.5 lbs Volume of Compacted Sample: 51.6 cm3

Table C-7 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 15 13.1 17.7 20 18.6 17 23.8 30 20 20 29.1 40 21.9 21.5 33 50 22.7 23.2 36.6 60 23.2 25.2 38.9 70 23.9 26.8 40.8 80 24.2 28.1 41.5 90 22.2 29.1 44.1 100 21.5 30.1 45.5 110 21.9 30.7 46.8 120 21.9 31.4 47.7 130 21.9 32.7 48.4 140 21.7 33.4 49.7 150 21.9 34 50.7 160 21.5 35 51.7 170 21.5 35.3 52 180 21.5 36.6 53 190 21.9 36.9 54.3 200 22.2 36.9 54.6 210 21.9 37.2 54.6 220 21.9 38 55.6 230 21.9 38.2 56.2 240 21.9 38.9 56.6 250 22.2 39.2 57.6 260 22.9 39.9 57.6 270 22.6 39.9 58.2 280 22.2 40.2 58.5 290 21.9 40.8 59.2 300 21.9 41.2 59.8 310 21.5 41.2 60.2 320 21.9 41.2 61.1 330 22.6 41.2 60.5 340 22.6 41.2 60.5 350 22.6 43.5 61.1

1

12

135

Direct Shear Test Data

Project: Cedar City Landslide Test No: 2 Sample Description: Tan to beige colluvial soil, at natural water content

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 21.9 lbs, 42.3 lbs, 58.9 lbs Volume of Compacted Sample: 51.6 cm3

Table C-8 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 7.5 15.4 17.3 20 9.3 19.6 22.6 30 11.1 22.6 26.7 40 12.1 25.2 26.5 50 13.2 27.1 30.7 60 14.4 28.8 33.7 70 15.4 30.4 36.3 80 16.5 31.4 38.4 90 18.0 32.5 40.4 100 18.5 34.2 42.2 110 18.6 35.3 44.0 120 19.0 36.1 44.6 130 19.6 36.5 45.6 140 19.9 37.9 46.4 150 20.3 38.3 48.1 160 20.8 38.9 49.1 170 20.9 39.9 50.0 180 21.1 40.2 51.2 190 21.3 40.9 52.3 200 21.4 41.2 53.3 210 21.4 41.5 53.8 220 21.6 41.7 54.3 230 21.6 41.5 55.3 240 21.6 41.7 55.6 250 21.7 41.5 55.9 260 21.6 40.9 55.9 270 21.6 41.7 56.9 280 21.3 42.2 57.1 290 21.3 42.2 57.2 300 20.8 42.3 57.2 310 20.9 41.9 57.6 320 21.9 41.7 57.9 330 58.9 340 350

1

12

136

Direct Shear Test Data

Project: Cedar City Landslide Test No: 3 Sample Description: Tan to beige colluvial soil, at natural water content

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 22.2 lbs, 42.2 lbs, 58.0 lbs Volume of Compacted Sample: 51.6 cm3

Table C-9 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 9.2 17.0 18.8 20 11.4 21.1 23.5 30 13.6 24.4 28.3 40 15.0 26.8 32.4 50 16.0 28.4 38.4 60 17.2 29.4 38.3 70 18.1 30.1 40.4 80 19.0 31.4 42.2 90 19.3 33.5 44.6 100 19.9 34.7 46.9 110 20.9 36.6 48.2 120 20.9 37.8 49.4 130 20.9 37.9 51.0 140 21.3 38.3 52.3 150 21.3 38.9 53.6 160 21.3 39.4 54.6 170 21.6 40.2 55.3 180 21.4 40.5 55.9 190 21.7 41.2 56.6 200 21.9 40.9 57.1 210 21.9 40.9 57.4 220 21.6 40.4 57.6 230 22.1 41.2 57.6 240 22.2 41.9 57.6 250 21.9 42.2 57.6 260 21.6 41.9 58.0 270 21.3 42.0 57.7 280 21.9 42.2 57.6 290 21.9 42.2 57.6 300 22.1 42.2 56.9 310 22.1 42.0 57.6 320 22.2 42.2 330 340 350

1

12

137

Direct Shear Test Data

Project: Cedar City Landslide Test No: 1 Sample Description: Tan to beige dried colluvial soil, on top of tan to beige sandstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 28.4 lbs, 51.3 lbs, 81.8 lbs Volume of Compacted Sample: 25.8 cm3

Table C-10 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 10.5 19.0 40.9 20 18.3 26.3 49.4 30 31.1 37.1 57.2 40 32.0 48.1 62.8 50 28.4 51.3 67.4 60 25.2 47.4 73.9 70 22.7 45.5 81.8 80 21.6 43.5 76.2 90 21.9 41.2 76.2 100 20.3 38.9 69.7 110 19.1 36.0 66.1 120 18.0 35.2 64.1 130 18.0 35.0 61.5 140 17.5 34.0 60.2 150 17.7 33.4 58.5 160 17.5 32.4 58.2 170 17.3 31.7 54.3 180 17.3 30.9 54.4 190 17.3 31.1 53.3 200 16.7 31.7 52.6 210 16.4 31.1 50.7 220 16.7 30.7 49.2 230 16.4 31.1 50.7 240 16.4 31.4 49.7 250 16.7 30.1 49.1 260 16.5 29.4 49.4 270 16.0 29.1 49.4 280 16.4 29.4 49.2 290 16.7 29.3 47.7 300 16.7 28.8 46.8 310 16.5 29.3 46.8 320 16.5 29.8 49.4 330 16.7 30.2 51.5 340 16.5 31.1 52.3 350 16.4 29.8 53.0

1

12

138

Direct Shear Test Data

Project: Cedar City Landslide Test No: 2 Sample Description: Tan to beige dried colluvial soil, on top of tan to beige sandstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 26.2 lbs, 44.8 lbs, 57.2 lbs Volume of Compacted Sample: 25.8 cm3

Table C-11 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 17.7 24.5 18.6 20 26.2 36.0 38.4 30 25.8 40.2 50.2 40 23.5 43.8 55.6 50 22.9 44.8 57.2 60 21.9 40.5 57.2 70 19.6 37.9 55.3 80 19.3 37.0 52.3 90 18.5 37.3 50.4 100 17.7 37.0 48.6 110 17.8 36.6 49.4 120 18.6 34.0 49.2 130 17.3 33.4 49.1 140 16.4 34.3 49.7 150 16.7 33.4 52.0 160 16.4 33.7 50.8 170 15.4 33.7 48.9 180 15.0 32.0 50.0 190 14.7 31.4 48.1 200 14.7 30.7 47.4 210 14.1 30.2 47.7 220 14.2 30.4 48.1 230 14.1 32.0 49.1 240 14.1 31.7 48.7 250 14.4 32.7 49.4 260 14.1 32.0 48.1 270 14.1 30.7 48.7 280 15.4 30.1 47.3 290 15.4 29.8 48.4 300 14.7 30.1 48.4 310 14.4 29.9 47.7 320 13.7 29.4 48.1 330 14.4 29.8 47.4 340 13.7 30.1 46.8 350 14.6 30.1 48.1

1

12

139

Direct Shear Test Data

Project: Cedar City Landslide Test No: 3 Sample Description: Tan to beige dried colluvial soil, on top of tan to beige sandstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 24.5 lbs, 54.9 lbs, 71.6 lbs Volume of Compacted Sample: 25.8 cm3

Table C-12 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 16.4 26.2 29.1 20 20.9 39.9 46.4 30 23.4 48.1 57.2 40 24.2 54.9 63.4 50 24.0 54.9 68.0 60 23.2 51.5 71.6 70 24.5 53.6 67.4 80 22.2 54.4 63.8 90 23.7 54.0 63.4 100 21.6 54.3 63.9 110 20.9 51.3 61.1 120 19.6 50.0 63.4 130 19.0 46.6 57.9 140 18.6 45.5 59.8 150 18.1 44.8 59.5 160 17.7 42.8 56.6 170 17.3 41.5 55.6 180 17.7 41.2 54.6 190 16.7 36.0 54.6 200 17.7 35.3 53.0 210 18.3 35.3 53.1 220 17.0 34.0 52.2 230 17.0 33.7 52.3 240 17.0 33.4 51.0 250 16.7 33.5 48.4 260 15.9 35.6 48.4 270 16.8 38.9 46.4 280 17.0 36.3 46.1 290 17.2 36.0 47.9 300 17.3 36.6 47.3 310 17.7 35.3 48.7 320 16.8 36.3 49.4 330 17.3 33.7 50.7 340 18.0 33.7 51.3 350 19.9 32.4 52.3

1

12

140

Direct Shear Test Data

Project: Cedar City Landslide Test No: 1 Sample Description: Tan to beige colluvial soil at natural water content, on top of tan to beige sandstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 23.5 lbs, 38.9 lbs, 57.2 lbs Volume of Compacted Sample: 25.8 cm3

Table C-13 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 15.7 16.4 18.3 20 18.6 18.3 28.1 30 21.6 22.6 35.5 40 23.1 25.5 41.0 50 23.2 28.4 39.9 60 23.2 30.4 51.0 70 23.2 32.4 54.3 80 22.6 34.7 57.2 90 22.9 36.0 54.6 100 23.5 36.6 51.7 110 23.2 36.8 54.0 120 22.2 37.0 53.3 130 21.3 37.0 53.0 140 21.6 37.6 52.6 150 21.6 37.8 52.2 160 20.3 37.3 53.6 170 20.3 37.8 53.0 180 19.9 37.3 53.0 190 20.4 37.6 53.5 200 19.9 37.3 51.3 210 19.5 37.3 52.8 220 19.6 36.5 52.3 230 19.0 36.6 53.6 240 18.6 38.1 53.6 250 19.3 37.9 53.3 260 19.3 38.3 52.2 270 19.6 37.6 51.0 280 20.1 38.9 51.3 290 19.3 38.6 52.2 300 19.5 38.7 51.5 310 18.0 38.3 51.3 320 18.0 37.6 50.8 330 17.7 37.9 51.3 340 17.5 37.6 52.0

350 17.0 37.3 52.2 1

12

141

Direct Shear Test Data

Project: Cedar City Landslide Test No: 2 Sample Description: Tan to beige colluvial soil at natural water content, on top of tan to beige sandstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 23.5 lbs, 35.3 lbs, 54.3 lbs Volume of Compacted Sample: 25.8 cm3

Table C-14 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 14.2 19.6 18.6 20 17.7 24.5 23.5 30 20.9 27.5 29.8 40 22.9 30.1 35.3 50 23.5 31.7 38.4 60 23.4 32.4 42.0 70 21.6 34.5 44.8 80 20.6 34.7 47.4 90 20.6 35.3 49.4 100 20.8 34.3 51.3 110 20.6 33.7 52.6 120 20.4 32.9 53.3 130 20.1 32.7 53.0 140 19.9 32.7 53.3 150 19.9 32.5 53.3 160 19.6 32.7 53.1 170 19.6 32.4 53.3 180 18.8 32.4 53.0 190 19.0 31.7 53.3 200 19.0 32.4 53.0 210 19.3 32.7 54.0 220 19.0 32.9 54.0 230 18.6 32.9 53.6 240 19.0 33.4 52.3 250 18.6 33.4 54.3 260 19.3 33.8 53.8 270 19.9 33.7 53.8 280 18.6 33.4 54.0 290 18.0 33.0 53.0 300 18.0 33.0 53.3 310 18.0 32.7 52.3 320 17.7 32.9 52.6 330 18.3 33.0 51.2 340 17.5 33.0 52.3

1

350 17.7 33.4 53.3 12

142

Direct Shear Test Data

Project: Cedar City Landslide Test No: 3 Sample Description: Tan to beige colluvial soil at natural water content, on top of tan to beige sandstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 23.5 lbs, 35.6 lbs, 58.2 lbs Volume of Compacted Sample: 25.8 cm3

Table C-15 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 16.4 14.9 19.6 20 19.1 18.3 26.0 30 21.6 21.3 37.9 40 22.6 25.5 40.5 50 23.5 28.0 45.1 60 23.4 30.2 50.0 70 22.6 31.4 56.9 80 22.1 32.7 58.2 90 21.9 33.0 57.2 100 21.9 34.7 54.4 110 22.1 33.7 50.7 120 21.9 33.4 53.3 130 20.9 33.5 51.3 140 20.3 33.7 48.4 150 19.9 34.0 47.4 160 19.0 34.7 48.4 170 18.5 34.0 47.6 180 18.3 33.7 48.1 190 18.0 34.7 48.1 200 18.6 34.7 48.1 210 18.5 35.0 48.4 220 18.3 35.0 48.7 230 18.3 35.0 49.4 240 19.3 35.3 49.5 250 18.6 35.0 49.7 260 17.7 35.2 50.4 270 18.0 35.0 50.7 280 18.3 35.6 51.0 290 18.3 35.3 51.5 300 18.5 34.7 52.6 310 18.3 34.5 52.6 320 18.3 33.7 51.0 330 17.7 33.7 51.0 340 18.3 34.7 52.0

1

350 18.5 35.3 52.3 12

143

Direct Shear Test Data

Project: Cedar City Landslide Test No: 1 Sample Description: Tan to beige colluvial dried soil, on top dark grey siltstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 18.1 lbs, 33.8 lbs, 49.7 lbs Volume of Compacted Sample: 25.8 cm3

Table C-16 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 17.7 27.1 30.4 20 17.0 30.1 39.1 30 17.7 29.1 43.8 40 18.1 29.4 44.8 50 17.0 29.8 43.3 60 16.0 30.2 43.2 70 14.7 30.4 43.8 80 15.0 30.4 43.8 90 14.1 30.7 43.3 100 13.7 31.4 44.8 110 13.9 31.2 43.8 120 13.9 31.1 44.8 130 13.4 30.7 44.8 140 13.7 31.1 45.1 150 13.7 31.2 44.8 160 13.7 31.1 45.1 170 13.7 31.4 45.8 180 13.1 31.7 45.8 190 13.4 31.7 45.8 200 13.1 31.7 46.1 210 12.6 32.0 46.8 220 12.3 32.0 47.4 230 12.4 32.4 47.4 240 13.1 32.7 47.7 250 12.4 32.9 48.1 260 13.1 32.7 48.4 270 12.6 32.7 48.4 280 12.1 32.4 48.4 290 12.4 32.7 48.7 300 12.4 32.7 48.7 310 12.3 32.4 49.1 320 12.3 32.0 49.1 330 12.8 33.7 48.7 340 13.1 33.7 48.6 350 13.4 33.8 49.7

1

12

144

Direct Shear Test Data

Project: Cedar City Landslide Test No: 2 Sample Description: Tan to beige colluvial dried soil, on top dark grey siltstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 20.9 lbs, 33.0 lbs, 43.2 lbs Volume of Compacted Sample: 25.8 cm3

Table C-17 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 8.8 28.1 23.9 20 18.0 33.0 37.6 30 20.9 32.0 43.2 40 19.5 31.1 41.0 50 19.9 30.7 39.9 60 19.8 30.1 39.6 70 19.0 29.8 38.9 80 19.3 29.6 38.9 90 18.6 29.1 38.3 100 18.8 29.8 38.3 110 18.6 30.1 39.9 120 18.3 29.4 39.2 130 18.3 29.1 38.9 140 18.5 28.8 38.3 150 18.3 29.1 39.1 160 18.3 29.4 38.9 170 18.6 29.1 39.6 180 18.6 29.4 39.6 190 18.6 29.3 39.9 200 19.0 29.1 39.4 210 19.1 29.1 39.6 220 19.3 29.3 39.2 230 19.1 29.4 39.9 240 19.0 29.4 39.9 250 19.0 29.6 40.1 260 19.3 29.4 39.2 270 19.5 29.4 39.4 280 19.8 29.1 39.9 290 19.6 29.8 39.2 300 19.3 30.4 39.2 310 19.6 30.1 39.2 320 19.6 29.4 38.7 330 19.9 29.3 40.2 340 19.6 29.4 40.2 350 18.6 30.4 40.2

1

12

145

Direct Shear Test Data

Project: Cedar City Landslide Test No: 3 Sample Description: Tan to beige colluvial dried soil, on top dark grey siltstone

Applied Load: 25 lbs, 50 lbs, 75 lbs Peak Shear Load: 20.9 lbs, 37.9 lbs, 54.0 lbs Volume of Compacted Sample: 25.8 cm3

Table C-18 Normal Load: 25 lbs 50 lbs 75 lbs Displacement (0.001 in) Force (lbs) Force (lbs) Force (lbs) 10 16.7 23.2 32.4 20 20.3 34.3 37.9 30 20.9 32.7 44.6 40 19.0 37.9 45.5 50 18.3 34.0 46.1 60 17.7 30.9 47.1 70 17.2 30.7 47.4 80 17.3 30.4 47.4 90 16.2 29.8 47.6 100 16.0 29.4 47.4 110 17.0 29.4 48.7 120 16.4 29.4 48.7 130 16.0 29.1 49.1 140 15.7 28.8 48.7 150 15.4 27.5 48.4 160 15.4 28.1 48.4 170 15.7 28.8 49.7 180 15.9 29.1 49.4 190 15.7 28.8 50.0 200 15.9 28.8 50.4 210 15.9 28.4 50.5 220 15.4 29.1 50.7 230 15.4 28.4 50.7 240 15.7 29.1 51.7 250 15.9 29.4 51.7 260 16.4 29.1 52.3 270 16.0 29.3 52.3 280 16.5 28.8 53.0 290 17.3 29.4 52.3 300 17.3 28.4 52.6 310 17.0 28.4 52.6 320 17.0 28.1 52.3 330 16.8 28.3 51.7 340 16.0 27.8 52.6 350 17.0 29.4 54.0

1

12

90

80

70

60

50

25 lbs

40 50 lbs

Shear (lbs)ForceShear 75 lbs

30

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

1

Figure C-5: Stress-Strain Plots for Dry Colluvial Soil, Test 1. 46

70

60

50

40

25 lbs 50 lbs 30

Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-6: Stress-Strain Plots for Dry Colluvial Soil, Test 2.

1

47

70

60

50

40

25 lbs 50 lbs 30 Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-7: Stress-Strain Plots for Dry Colluvial Soil, Test 3.

1

48

70

60

50

40 25 lbs 50 lbs

30 75 lbs Shear (lbs)ForceShear

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-8: Stress-Strain Plots for Colluvial Soil at Natural Water Content, Test 1.

1

49

70

60

50

40

25 lbs 50 lbs 30 Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 Shear Displacement (0.001 in)

1 Figure C-9: Stress-Strain Plots for Colluvial Soil at Natural Water Content, Test 2. 50

70

60

50

40

25 lbs 50 lbs 30 Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 Shear Displacement (0.001 in)

Figure C-10: Stress-Strain Plots for Colluvial Soil at Natural Water Content, Test 3.

1

51

90

80

70

60

50 25 lbs 40 50 lbs

Shear (lbs)ForceShear 75 lbs

30

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-11: Stress-Strain Plots for Dry Colluvial Soil-Dakota Sandstone Contact, Test 1.

1

52

70

60

50

40

25 lbs 50 lbs 30 Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-12: Stress-Strain Plots for Dry Colluvial Soil-Dakota Sandstone Contact, Test 2. 1

53

80

70

60

50

40 25 lbs 50 lbs

Shear (lbs)ForceShear 75 lbs 30

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-13: Stress-Strain Plots for Dry Colluvial Soil-Dakota Sandstone Contact, Test 3.

1

54

70

60

50

40

25 lbs 50 lbs 30 Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-14: Stress-Strain Plots for Colluvial Soil at Natural Water Content-Dakota Sandstone Contact, Test 1.

1

55

70

60

50

40

25 lbs 50 lbs 30 Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

1

Figure C-15: Stress-Strain Plots for Colluvial Soil at Natural Water Content-Dakota Sandstone Contact, Test 2. 56

70

60

50

40

25 lbs 50 lbs 30

Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

1

Figure C-16: Stress-Strain Plots for Colluvial Soil at Natural Water Content-Dakota Sandstone Contact, Test 3. 57

60

50

40

25 lbs 30 50 lbs

Shear (lbs)ForceShear 75 lbs

20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-17: Stress-Strain Plots for Dry Colluvial Soil-Tropic Shale Contact, Test 1.

1

58

50

45

40

35

30

25 25 lbs 50 lbs

Shear (lbs)ForceShear 20 75 lbs

15

10

5

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-18: Stress-Strain Plots for Dry Colluvial Soil-Tropic Shale Contact, Test 2. 1

59

60

50

40

30 25 lbs

50 lbs Shear (lbs)ForceShear 75 lbs 20

10

0 0 50 100 150 200 250 300 350 400 Shear Displacement (0.001 in)

Figure C-19: Stress-Strain Plots for Dry Colluvial Soil-Tropic Shale Contact, Test 3.

1

60

90

80

70 φp = 46° cp = 0 psi

60

50 φr = 44° cr = 0 psi Peak Values 40

Residual Values Shear LoadShear(lbs)

30

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-20: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil, Test 1.

1

61

70

60 φp = 35.5° cp = 2.33 psi

50

40 φr = 34° cr = 1 psi Peak Values

30 Residual Values Shear Load (lbs) LoadShear

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

1 Figure C-21: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil, Test 2. 62

70

60 φp = 38° cp = 2 psi

50

φr = 36° 40 cr = 0.75 psi

Peak Values

30 Residual Values Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-22: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil, Test 3. 1

63

70

60

φp = 35.5° cp = 1.75 psi

50

40

Peak Values

30 Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-23: Mohr Envelopes for Peak Strength for Colluvial Soil at Natural Water Content, Test 1.

1

64

70

60

φp = 38.5° cp = 0.5 psi

50

40

Peak Values

30 Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-24: Mohr Envelopes for Peak Strength for Colluvial Soil at Natural Water Content, Test 2.

1

65

70

60

φp = 37° cp = 0.75 psi

50

40

Peak Values

30 Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

1

Figure C-25: Mohr Envelopes for Peak Strength for Colluvial Soil at Natural Water Content, Test 3. 66

90

80

φp = 47° 70 cp = 0 psi

60

50

Peak Values 40 Residual Values

Shear LoadShear(lbs) φr = 34° cr = 0 30 psi

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-26: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil-Dakota Sandstone Contact, Test 1. 1

67

70

60

φp = 36° cp = 1.7 psi

50

40

φr = 32.5° Peak Values c = 0 psi

30 r Residual Values Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

1

Figure C-27: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil-Dakota Sandstone Contact, Test 2. 68

80

70

φp = 42° cp = 1.6 psi 60

50

40 φr = 36° Peak Values c = 0 psi

r Residual Values Shear LoadShear(lbs) 30

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-28: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil-Dakota Sandstone Contact, Test 3.

1

69

70

60

φp = 34° 50

cp = 1.5 psi

40 φr = 34° cr = 0.63 psi Peak Values

30 Residual Values Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-29: Mohr Envelopes for Peak and Residual Strength for Colluvial Soil at Natural Water Content-Dakota

1 Sandstone Contact, Test 1. 70

60

50

φp = 33° cp = 1.5 psi

40

φr = 33° cr = 0.73 psi 30 Peak Values

Residual Values Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-30: Mohr Envelopes for Peak and Residual Strength for Colluvial Soil at Natural Water Content-Dakota

1

Sandstone Contact, Test 2. 71

70

60

φp = 36.5°

50 cp = 0.53 psi

40

φr = 35° Peak Values cr = 0 psi

30 Residual Values Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-31: Mohr Envelopes for Peak and Residual Strength for Colluvial Soil at Natural Water Content-Dakota

1 Sandstone Contact, Test 3. 72

60

50

φp = 32° cp = 0.63 psi

40

30

Peak Values Shear LoadShear(lbs)

20

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-32: Mohr Envelopes for Peak Strength for Dry Colluvial Soil -Tropic Shale Contact, Test 1. 1

73

50

45

φp = 25° 40 cp = 2.3 psi

35

φr = 22°

30 cr = 2.2 psi

25 Peak Values Residual Values

Shear LoadShear(lbs) 20

15

10

5

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

1

Figure C-32: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil -Tropic Shale Contact, Test 2. 74

60

50 φp = 33° cp = 1.3 psi

40

30 Peak Values

Residual Values Shear LoadShear(lbs)

φr = 25° 20 cr = 0.75 psi

10

0 0 10 20 30 40 50 60 70 80 Normal Load (lbs)

Figure C-33: Mohr Envelopes for Peak and Residual Strength for Dry Colluvial Soil -Tropic Shale Contact, Test 3.

1

75

176

Unconfined Compression Test Data

Project: Cedar City Landslide Boring: MP8-1 Depth: 167.0 – 169.0 ft Test No: 1

Sample Description: Tan to grey, medium to fine grained sandstone

Sample Dimensions:

Measurement Diameter (cm) Length (cm) L/D ratio 1 4.9 12.05 2.5 2 4.95 12 2.4 3 5 11.95 2.4 4 4.9 11.9 2.4 5 4.9 12 2.4

Average L/D Ratio = 2.43 Average Length (L) = 12 in Failure Load (P) = 11766 lbs Sample Weight (w) = 543.5 g x-sec area (A) of sample = 3 in2 Sample Volume (v) = 228.7 cm3 qu (psi) = P/A Dry Density = 142.9 pcf 3 qu = 3976.6 psi 2.29 g/cm Loading Rate = 19.9 lbs/min

Failed Sample

1

67

177

Unconfined Compression Test Data

Project: Cedar City Landslide Boring: MP8-1 Depth: 167.0 – 169.0 ft Test No: 2

Sample Description: Tan to grey, medium to fine grained sandstone

Sample Dimensions:

Measurement Diameter (cm) Length (cm) L/D ratio 1 4.95 10.58 2.1 2 4.98 10.6 2.1 3 4.92 10.57 2.2 4 4.93 10.49 2.1 5 4.97 10.51 2.1

Average L/D Ratio = 2.13 Average Length (L) = 10.6 in Failure Load (P) = 14020 lbs Sample Weight (w) = 483.8 g x-sec area (A) of sample = 3 in2 Sample Volume (v) = 203.03 cm3 qu (psi) = P/A Dry Density = 148.7 pcf 3 qu = 4700.2 psi 2.38 g/cm Loading Rate = 17.6 lbs/min

Failed Sample

1

67

178

Unconfined Compression Test Data

Project: Cedar City Landslide Boring: MP8-1 Depth: 167.0 – 169.0 ft Test No: 3

Sample Description: Tan to grey, medium to fine grained sandstone

Sample Dimensions:

Measurement Diameter (cm) Length (cm) L/D ratio 1 4.95 9.76 1.97 2 4.96 9.7 1.96 3 4.95 9.78 1.98 4 4.99 9.83 1.97 5 5 9.83 1.96

Average L/D Ratio = 1.97 Average Length (L) = 9.78 in Failure Load (P) = 10322 lbs Sample Weight (w) = 425.8 g x-sec area (A) of sample = 3 in2 Sample Volume (v) = 189.73 cm3 qu (psi) = P/A Dry Density = 140.0 pcf 3 qu = 3432.6 psi 2.24 g/cm Loading Rate = 15.6 lbs/min

Failed Sample

1

67

179

Unconfined Compression Test Data

Project: Cedar City Landslide Boring: MP8-1 Depth: 167.0 – 169.0 ft Test No: 4

Sample Description: Tan to grey, medium to fine grained sandstone

Sample Dimensions:

Measurement Diameter (cm) Length (cm) L/D ratio 1 4.95 9.6 1.93 2 4.96 9.79 1.97 3 5 9.76 1.95 4 5 9.72 1.94 5 4.98 9.66 1.94

Average L/D Ratio = 1.95 Average Length (L) = 9.71 in Failure Load (P) = 16532 lbs Sample Weight (w) = 494.3 g x-sec area (A) of sample = 3 in2 Sample Volume (v) = 189.13 cm3 qu (psi) = P/A Dry Density = 142.9 pcf 3 qu = 5480.2 psi 2.61 g/cm Loading Rate = 21.8 lbs/min

Failed Sample

1

67

APPENDIX D

DATA ANALYSIS

180

Figure D-1: Contouring of Straight Cliffs Sandstone discontinuities using the DIPS software.

181

Figure D-2: Contouring of Dakota Sandstone discontinuities using the DIPS software.

182

Figure D-3: Contouring of discontinuities from both the Dakota Sandstone and the Straight Cliffs Sandstone using the DIPS software.

183

Figure D-4: Kinematic Analysis of Hazard Potential within the Straight Cliffs Sandstone.

184

Figure D-5: Stability analysis for dry colluvial soil-Tropic Shale parameters, using both the Bishop and the Janbu simplified methods. 185

Figure D-6: Stability analysis for dry colluvial soil-Dakota Sandstone parameters, using both the Bishop and the Janbu simplified methods. 186

Figure D-7: Stability analysis for dry average soil-bedrock parameters, for Bishop simplified method. 187

188

Figure D-8: Stability analysis for dry average soil-bedrock parameters, for Janbu simplified method.

189

Table D-1: Variation of Factor of Safety with varying density values

Density (pcf) Density (kN/m3) Factor of Safety 102.5 16.1 1.016 105.0 16.5 1.016 108.2 17.0 1.016 111.4 17.5 1.016 112.0 17.3 1.016 114.6 18.0 1.016 117.8 18.5 1.016 121.0 19.0 1.015 124.1 19.5 1.015 126.7 19.9 1.015

187

Figure D-9: Stability analysis for the colluvial soil-Tropic Shale parameters, fully saturated, for both Bishop and Janbu 190

simplified methods.

Figure D-10: Stability analysis for the colluvial soil-Dakota Sandstone parameters, fully saturated, for both Bishop and

Janbu simplified methods. 191

Figure D-11: Stability analysis for the average soil-bedrock parameters, fully saturated, for both Bishop and Janbu 192

simplified methods.

Figure D-12: SLIDE Analysis with the water table height at 3.3 ft (1 m) above the contact, Φ = 29°, for Bishop 193

simplified method.

Figure D-13: SLIDE Analysis with the water table height at 3.3 ft (1 m) above the contact, Φ = 29°, for Janbu simplified

194 method.

Figure D-14: SLIDE Analysis with the water table height at 11.7 ft (3.5m) above the contact, Φ = 30°, for Bishop 195 simplified method.

Figure D-15: SLIDE Analysis with the water table height at 11.7 ft (3.5m) above the contact, Φ = 30°, for Janbu simplified method. 196

Figure D-16: SLIDE Analysis with the water table height at 23.7 ft (7.2 m) above the contact, Φ = 32°, for Bishop simplified method. 197

Figure D-17: SLIDE Analysis with the water table height at 23.7 ft (7.2 m) above the contact, Φ = 32°, for Janbu simplified method. 198

Figure D-18: SLIDE Analysis with the water table height at 39.4 ft (11.9 m) above the contact, Φ = 34°, for Bishop

simplified method. 199

Figure D-19: SLIDE Analysis with the water table height at 39.4 ft (11.9 m) above the contact, Φ = 34°, for Janbu

200 simplified method.