Warning Concerning Copyright Restrictions The Copyright Law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specified conditions is that the photocopy or reproduction is not to be used for any purpose other than private study, scholarship, or research. If electronic transmission of reserve material is used for purposes in excess of what constitutes "fair use," that user may be liable for copyright infringement. (Photo: Kennecott) Bingham Canyon Landslide: Analysis and Mitigation GE 487: Geological Engineering Design Spring 2015 Jake Ward 1 Honors Undergraduate Thesis Signatures: 2 Abstract On April 10, 2013, a major landslide happened at Bingham Canyon Mine near Salt Lake City, Utah. The Manefay Slide has been called the largest non-volcanic landslide in modern North American history, as it is estimated it displaced more than 145 million tons of material. No injuries or loss of life were recorded during the incident; however, the loss of valuable operating time has a number of slope stability experts wondering how to prevent future large-scale slope failure in open pit mines. This comprehensive study concerns the analysis of the landslide at Bingham Canyon Mine and the mitigation of future, large- scale slope failures. The Manefay Slide was modeled into a two- dimensional, limit equilibrium analysis program to find the controlling factors behind the slope failure. It was determined the Manefay Slide was a result of movement along a saturated, bedding plane with centralized argillic alteration. Recommendations for mitigating future slope failure are provided based on the results of the limit equilibrium analyses. 3 Table of Contents Abstract . 2 List of Figures . 5 List of Tables . 8 Introduction . 10 History of Bingham Canyon Mine . 12 i. Utah and Mining . 12 ii. Bingham Canyon Mine: Discovery and Development . 13 iii. “The Richest Hole on Earth” . 15 iv. World Wars and the Great Depression . 18 v. The Latter 20th Century and Bingham Canyon Mine Today . 20 Environmental Legacy of Bingham Canyon Mine . 22 Social and Economic Impact of the Manefay Slide . 26 Geology of the Bingham Canyon Mine . 28 i. Regional Geology: The Oquirrh Mountains . 28 ii. Geologic Rock Types . 29 iii. Structural Geology . 41 iv. Economic Geology . 47 v. Groundwater Hydrology . 58 vi. Seismicity . 60 Geotechnical Monitoring . 61 Theory: Slope Stability . 69 i. Contributory Processes . 69 ii. Challenges of Slope Stability . 74 iii. Typical Failure Mechanisms . 78 4 iv. Mohr-Coulomb Failure Relationship . 84 v. Slope Stability Analysis Methods . 86 Open Pit Mine Design & Slope Stability . 96 i. Economics of Open Pit Mining . 97 ii. Architecture of Open Pit Mining . 99 Methods . 101 i. Slide by Rocscience, Inc. 101 ii. Determining Rock Mass Properties . 104 iii. Slide Testing . 105 Analysis . 107 Discussion . 116 i. Discussion . 116 ii. Recommendations for Mitigating Future Slope Failure . 119 iii. Run Out Prediction: Volume-Fahrböschung Relationship . 121 iv. Future Work . 123 References . 124 Appendix A: Tabled Data from Direct Shear Tests . 129 Appendix B: Tabled Data from Slide . 133 Appendix C: Slope Geometry Input for Slide . 145 5 List of Figures Figure 1. Manefay Slide at Bingham Canyon Mine. Figure 2. Utah Territory map. Figure 3. Artist’s view of Bingham Canyon Mine. Figure 4. Bingham Canyon Mine today. Figure 5. Boundary of Bingham NPL Zone. Figure 6. Uinta Axis and Wasatch Fault map. Figure 7. Stratigraphic column. Figure 8. Dikes and sills in Bingham Canyon Mine open pit Figure 9. Distribution of igneous rock map. Figure 10. Bingham Syncline. Figure 11. Structural map of Bingham Canyon Mine. Figure 12. Alteration map. Figure 13. Ore body cross section. Figure 14. Economic mineral distribution map. Figure 15. Aquifer map, Salt Lake County. Figure 16. USGS 2014 Earthquakes Hazard Map. Figure 17. Rio Tinto’s TRACK program. Figure 18. A Robotic Total Station (RTS). Figure 19. GroundProbe Slope Stability Radar (SSR). Figure 20. IBIS System. Figure 21. Uniaxial strength and alteration. Figure 22. Effect of water pressure on Mohr’s Circle. Figure 23. Drainage methods. Figure 24. Spatial variability of rock mass. 6 Figure 25. Discontinuities and scale. Figure 26. Plane failure diagram. Figure 27. Wedge failure diagram. Figure 28. Circular failure diagram. Figure 29. Toppling failure diagram. Figure 30. Buckling failure diagram. Figure 31. Mohr-Coulomb failure envelope. Figure 32. Typical kinematic analysis plots. Figure 33. Hoek and Bray (1981) slope height vs slope angle study. Figure 34. Inverse velocity plot. Figure 35. Inclined block. Figure 36. Inclined block with water pressure. Figure 37. Inclined block with rock bolt. Figure 38. Circular failure/ method of slices. Figure 39. Bingham Canyon Mine. Figure 40. 25 year copper price Figure 41. Slope geometry of open pit mine. Figure 42. Typical Slide plot. Figure 43. Slopes of failure surface in Slide. Figure 44. Water table in Slide. Figure 45. Quartzite Mohr-Coulomb plot. Figure 46. Argillic Clay Mohr-Coulomb plot. Figure 47. Preexisting discontinuity in quartzite, Slide. Figure 48. Water table in Slide. Figure 49. Factor of safety rankings. Figure 50. FoS plot, preexisting discontinuity in quartzite. 7 Figure 51. Average FoS by failure plane angle. Figure 52. FoS plot, failure plane in argillic clay. Figure 53. FoS plot, quartzite sliding on argillic clay. Figure 54. NOAA precipitation map, April 9, 2013. Figure 55. Side scarp diagram. Figure 56. Predicted vs actual run out. 8 List of Tables Table 1. Advanced limit equilibrium methods. Table 2. Quartzite strength properties, Styles et al. (2011) Table 3. Quartzite: 500 psi Normal Load. Table 4. Quartzite: 1000 psi Normal Load. Table 5. Quartzite: 1500 psi Normal Load. Table 6. Quartzite: 2000 psi Normal Load. Table 7. Quartzite: 2500 psi Normal Load. Table 8. Peak and residual values for quartzite. Table 9. Argillic Clay-Quartzite: 500 psi Normal Load. Table 10. Argillic Clay-Quartzite: 1000 psi Normal Load. Table 11. Argillic Clay-Quartzite: 1500 psi Normal Load. Table 12. Argillic Clay-Quartzite: 2000 psi Normal Load. Table 13. Argillic Clay-Quartzite: 2500 psi Normal Load. Table 14. Argillic Clay-Quartzite: 3000 psi Normal Load. Table 15. Failure Plane in Quartzite; Failure Plane: 15˚. DRY. Table 16. Argillic Clay Sliding on Quartzite; Failure Plane: 15˚. DRY. Table 17. Failure Plane in Argillic Clay; Failure Plane: 15˚. DRY. Table 18. Altered Limestone Sliding on Quartzite; Failure Plane: 15˚. Table 19. Failure Plane in Altered Limestone; Failure Plane: 15˚. DRY. Table 20. Quartzite Sliding on Argillic Clay; Failure Plane: 15˚. DRY. Table 21. Failure Plane in Quartzite; Failure Plane: 15˚. SAT. Table 22. Argillic Clay Sliding on Quartzite; Failure Plane: 15˚. SAT. Table 23. Failure Plane in Argillic Clay; Failure Plane: 15˚. SAT. Table 24. Altered Limestone Sliding on Quartzite; Failure Plane: 15˚. 9 Table 25. Failure Plane in Altered Limestone; Failure Plane: 15˚. SAT. Table 26. Quartzite Sliding on Argillic Clay; Failure Plane: 15˚. SAT. Table 27. Failure Plane in Quartzite; Failure Plane: 20˚. DRY. Table 28. Argillic Clay Sliding on Quartzite; Failure Plane: 20˚. DRY. Table 29. Failure Plane in Argillic Clay; Failure Plane: 20˚. DRY. Table 30. Altered Limestone Sliding on Quartzite; Failure Plane: 20˚. Table 31. Failure Plane in Altered Limestone; Failure Plane: 20˚. DRY. Table 32. Quartzite Sliding on Argillic Clay; Failure Plane: 20˚. DRY. Table 33. Failure Plane in Quartzite; Failure Plane: 20˚. SAT. Table 34. Argillic Clay Sliding on Quartzite; Failure Plane: 20˚. SAT. Table 35. Failure Plane in Argillic Clay; Failure Plane: 20˚. SAT. Table 36. Altered Limestone Sliding on Quartzite; Failure Plane: 20˚. Table 37. Failure Plane in Altered Limestone; Failure Plane: 20˚. SAT. Table 38. Quartzite Sliding on Argillic Clay; Failure Plane: 20˚. SAT. Table 39. Failure Plane in Quartzite; Failure Plane: 25˚. DRY. Table 40. Argillic Clay Sliding on Quartzite; Failure Plane: 25˚. DRY. Table 41. Failure Plane in Argillic Clay; Failure Plane: 25˚. DRY. Table 42. Altered Limestone Sliding on Quartzite; Failure Plane: 25˚. Table 43. Failure Plane in Altered Limestone; Failure Plane: 25˚. DRY. Table 44. Quartzite Sliding on Argillic Clay; Failure Plane: 25˚. DRY. Table 45. Failure Plane in Quartzite; Failure Plane: 25˚. SAT. Table 46. Argillic Clay Sliding on Quartzite; Failure Plane: 25˚. SAT. Table 47. Failure Plane in Argillic Clay; Failure Plane: 25˚. SAT. Table 48. Altered Limestone Sliding on Quartzite; Failure Plane: 25˚. Table 49. Failure Plane in Altered Limestone; Failure Plane: 25˚. SAT. Table 50. Quartzite Sliding on Argillic Clay; Failure Plane: 25˚. SAT. 10 Introduction Bingham Canyon Mine is located 18 miles southwest of Salt Lake City, Utah, and is one of the largest open pit mines in the world. The pit is approximately 3,900 feet deep and is more than 2.75 miles across. Bingham Canyon Mine has produced more copper—about 19 million tons—than any other mine in the world, and also produces gold, silver, and molybdenum (Rio Tinto Kennecott, 2013a). On April 10, 2013, a major landslide occurred in the northeastern pit wall, moving material at an average speed of 70 mph and burying the pit floor in 300 feet of dirt and rock (Carter, 2014; Pankow and Moore, 2014). The Manefay Slide has been called the largest non- volcanic landslide in modern North American history, displacing more than 145 million tons of material. The Manefay Slide even caused two seismic events registering 2.5 and 2.4 in magnitude, as well as 14 smaller earthquakes (Pankow and Moore, 2014; Carter, 2014). Fortunately, no one was injured or died because of the landslide. The mine’s geotechnical operations team used the data collected from several slope monitoring instruments to administer a preemptive response, suspending mining activities and clearing all personnel from the open pit.