University of Nevada Reno Residual Stress-Induced Failure Mechanisms of Three Types of Granodiorite, Central Sierra Nevada, Cali
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University of Nevada Reno / . Residual Stress-Induced Failure Mechanisms of Three Types of Granodiorite, Central Sierra Nevada, California A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geological Engineering by Kevin Patrick Roberts June 1990 i MINES LIBRARY V/iTSlS The thesis of Kevin Patrick Roberts is approved: g 2)-r Dean, Graduate School J University of Nevada Reno June 1990 11 ACKNOWLEDGEMENTS I would like to extend my gratitude to the faculty members of the University of Nevada who assisted me toward the successful completion of this project. I thank Dr. James R. Carr for his valuble advice on statistical analyses and data representation and Dr. Pierre Mousset-Jones for his critical review of the project. I would especially like to thank Dr. Robert J. Watters who, as the chairman of my advisory committee, initiated the study and patiently provided support and guidance through to its completion. Special thanks go to my fellow graduate students who assisted me during all phases of this undertaking. Particular thanks are due to Donald Chuck whose knowledge and skill in the .laboratory contributed greatly to the quality of this study. I would also like to thank Eric Rehwoldt for his help during the field phase of this study. Finally, I thank my family, particularly my parents, Neil Roberts and Peggy Berry, for all of their support and encouragement. Without their help, my educational endeavors would not have been possible. Ill ABSTRACT High near-surface compressive stress in massive granodiorite of the central Sierra Nevada produces natural rock failure characteristics occasionally seen in mining and quarrying operations. The principal component of the stress was elastically induced by erosional removal of overburden. Other contributions include stresses due to thermal fluctuations in the rock surface and gravitational loading. Granodiorite fails by stress-relief fracture exhibiting continuous parallelism with topography and a linearly increasing spacing with depth. Utilizing fracture mechanics priciples, a maximum stress estimate of 13 MPa at Tuolumne Meadows yields estimates of fracture toughness for Half Dome and Cathedral Peak granodiontes of 0.4 and 1.7 MPa(m) respectively. Compressive stresses of 13 and 32 MPa are required to initiate extension of maximum grain size microcracks for Cathedral Peak and Half Dome granodiorites, assuming a fracture toughness value of 1.6 MPa(m) obtained by averaging five values for granitic rock from the literature. Nine examples of gable mode buckling failure of surficial granodiorite slabs yield, through back-calculation, original .in-situ stresses ranging from 5 to 16 MPa. IV TABLE OF CONTENTS SIGNATURE PAGE...................................... i ACKNOWLEDGEMENTS........................... ii ABSTRACT............................................. iii TABLE OF CONTENTS................................... iv LIST OF FIGURES..................................... vii LIST OF TABLES...................................... xi CHAPTER 1 — INTRODUCTION.......................... 1 Introduction................................... 1 Scope and Purpose of Study.................... 2 Previous Work.................................. 3 Residual Stresses........................ 4 Mechanics of Failure From Residual Stresses.................................. 5 Case Histories........................... 6 CHAPTER 2 — LOCATION AND GEOLOGY.................. 10 Location of Study.............................. 10 Geology -- Cretaceous to Tertiary............ 14 Sierra Nevada Tectogenesis.............. 14 Emplacement of Plutons................... 15 Mokelumne Rocktype....................... 15 Tuolumne Geology......................... 17 Quaternary Geology............................ 2 3 Glacial Processes........................ 25 V Weathering Processes..................... 29 Pleistocene Glaciations................. 30 CHAPTER 3 — LABORATORY TESTING.................... 3 4 Tensile Strength............................... 35 Theoretical Principles of the Brazilian Method.................. 35 Tensile Test Procedure................... 38 Uniaxial Compressive Strength and Deformability.............................. 41 Test Preparation and Procedure.......... 41 The Stress-Strain Curve................. 43 Volumetric Strain........................ 47 Acoustic Emissions....................... 49 Strength Failure......................... 51 Test Results.............................. 55 CHAPTER 4 — ORIGINS OF STRESS AND STRAIN ENERGY.. 57 Origins of High Near-Surface Stress.......... 57 Tectonic Stress.......................... 57 Topographical Effects.................... 58 Thermal Stresses......................... 60 Erosional Unloading...................... 62 Strain Energy.................................. 67 Theory.................................... 67 Results For Tuolumne Granodiorites..... 7 0 CHAPTER 5 — TUOLUMNE SHEET FRACTURE.............. 7 3 Field Data Analysis........................... 73 vi Sheet Fracture Conformity With Topography.......................... 7 5 Sheet Thickness With Depth.............. 7 9 Fracture Mechanisms of Brittle Rock........... 8 5 Griffith Failure Criterion.............. 85 Linear Elastic Fracture Mechanics....... 88 Stress Intensity Factor.................. 88 Compression-induced Fracture Initiation...................... 90 Near-Surface Compressive Stress Analysis — LEFM....................... 92 CHAPTER 6 — SLAB BUCKLING FAILURE................. 97 Field Examples of Buckled Granodiorite Slabs.................... 9 7 Mechanisms of Buckling Failure............... 114 Buckling Modes............................ 114 Buckling Theory........................... 117 Buckling Stress Analysis...................... 119 CHAPTER 7 -- CONCLUSIONS............................ 12 2 Near-Surface Compressive Stress.............. 122 Failure Mechanisms............................. 125 Summary of Conclusions........................ 128 REFERENCES CITED.................................... 132 APPENDIX A — LABORATORY TEST RESULTS............. 13 7 APPENDIX B — METHOD OF BUCKLING STRESS BACK-CALCULATION............. 156 Vll LIST OF FIGURES Figure Page 2-1 General location map of study areas........ 11 2-2 Mokelumne study area........................ 12 2-3 Tuolumne study area.......................... 13 2-4 Photomicrograph of Granodiorite of Caples Lake................................ 16 2-5 Tuolumne bedrock geology.................... 18 2-6 Photomicrograph of Half Dome Granodiorite............................ 21 2-7 Photomicrograph of Cathedral Peak Granodiorite............................ 21 2-8 Stereoplot of Tuolumne poles to joint planes........................ 22 2-9 Photograph of jointing on Polly Dome....... 24 2-10 Photograph of regional extensional joint.... 24 2-11 Distribution of glacial load over bedrock undularion...................... 2 6 2-12 Crushing failure of subglacial bedrock..... 27 2- 13 A simple model of glacial abrasion......... 28 3- 1 Plot of Brazil test stress solution........ 37 3-2 The Brazil test.............................. 40 3-3 Photograph of UNR compression testing apparatus............................ 4 2 3-4 Extensometers attached to specimen......... 4 2 3-5 Stress-strain plot for specimen Kcl-3...... 45 3-6 Stress-volumetric strain curve for specimen Kcl-3........................... 48 3-7 Acoustic emissions signature for specimen Kcl-3................................ 51 Vlll Figure Page 3-8 Failed specimens of Kcl............. 53 3- 9 Failed specimens of Tuolumne Meadows granodiorites................ 54 4- 1 Topographic stress concentration... 59 4-2 Cube supporting three orthonormal stresses.. 63 4-3 Strain energy for initially stressed material.................... 68 4- 4 Strain energy with depth for Tuolumne granodiorites.......... 71 5- 1 Sheet structure data collection stations.... 74 5-2 Photograph of Half Dome Granodiorite sheets........................... 7 6 5-3 Histogram of slope and mean sheet fracture azimuth differences................. 77 5-4 Histogram of slope and mean sheet fracture dip angle differences.............. 7 8 5-5 All sheet thicknesses and depths... 82 5-6 Averages of sheet thicknesses and depths for sequences of eight sheets............... 83 5-7 Three modes of crack deformation... 89 5-8 Pre-existing closed crack under compression. 93 5-9 Compressive force required for crack extension............................... 9 3 5- 10 Stress required for crack extension in Tuolumne granodiorites.................... 9 5 6- 1 Buckled slab locations....................... 98 6-2 Photograph of Mokelumne buckled slab........ 99 6-3 Photograph of buckled slab #1................ 100 6-4 Photograph of buckled slab #2................ 100 6-5 Photograph of buckled slab #3................ 101 IX Figure Page 6-6 Photograph of buckled slab #4................ 101 6-7 Photograph of buckled slab #5................ 102 6-8 Photograph of buckled slab #6................ 102 6-9 Photograph of buckled slab #7................ 103 6-10 Photograph of buckled slab #8................ 103 6-11 Mokelumne River slope and compression axis.. 105 6-12 Buckled slab #1 slope and compression axis.. 106 6-13 Buckled slab #2 slope and compression axis.. 107 6-14 Buckled slab #3 slope and compression axis.. 108 6-15 Buckled slab #4 slope and compression axis.. 109 6-16 Buckled slab #5 slope and compression axis.. 110 6-17 Buckled slab #6 slope and compression axis.. Ill 6-18 Buckled slab #7 slope and compression axis.. 112