CEMEX Eliot Quarry. Lake A Evaluation Report. Alameda County, California

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Nicholas Johnston
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1 May 7, 2015

3 May 7, 2015 Project No. GT13-16 Prepared for: CEMEX 5180 Golden Foothills, Parkway El Dorado Hills, California Shoreline Drive, Ste. 6 Stockton, California Tel: Fax:

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5 TABLE OF CONTENTS TABLE OF CONTENTS iii 1. INTRODUCTION General Purpose SLOPE STABILITY ANALYSES Lake A Slope Stability Analyses Geologic Model Lake A, Profile A Lake A, Profile B Lake A, Profile C Lake A, Profile D Lake A Slope Stability Results CONCLUSIONS AND RECOMMENDATIONS REFERENCE LIMITATIONS APPENDIX A Slope Stability Analysis Profile A Static Analysis Seismic Analysis APPENDIX B Slope Stability Analysis Profile B Static Analysis Seismic Analysis APPENDIX C Slope Stability Analysis Profile C Static Analysis Seismic Analysis APPENDIX D Slope Stability Analysis Profile D Static Analysis Seismic Analysis APPENDIX E Slope Stability Analysis Profile D (After Grading) iii

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7400 Shoreline Drive, Stockton, California 95219 Suite 6 209-472-1822 Phone 209-472-0802 Fax william.kane@kanegeotech.com 1441 Kapiolani Boulevard Suite 1115 Honolulu, Hawaii 96814 808-356-2668 www.

Lake A is presently an inactive quarry that will eventually be the first link in the Chain of Lakes proposed by Alameda County Flood Control and Water Conservation District, Zone 7, Figure 1.

7 7400 Shoreline Drive, Stockton, California Suite Phone Fax william.kane@kanegeotech.com 1441 Kapiolani Boulevard Suite 1115 Honolulu, Hawaii INTRODUCTION 1.1 General (KANE GeoTech) was contracted by CEMEX, Inc. (CEMEX) to assess the slope stability of Lake A located in Livermore, California in Alameda County. Lake A is presently an inactive quarry that will eventually be the first link in the Chain of Lakes proposed by Alameda County Flood Control and Water Conservation District, Zone 7, Figure 1. The slope stability analysis of Lake A has been prepared to support the Reclamation Plan Amendment that CEMEX has submitted to Alameda County. Additional mining will not occur within Lake A. However, the reclamation of Lake A for use in the Chain of Lakes will include limited additional excavation in some areas and filling or grading of other areas. The geologic model, material properties, and seismic coefficients used in this evaluation report for Lake A are based on the information and interpretations presented in the accompanying Geotechnical Characterization Report and its Figure 1. Overview of Chain of Lakes

8 Page 2 supporting Appendices, which contain additional site background and information. Summaries of pertinent references and complete methodologies for analyses can also be found in the Geotechnical Characterization Report. 1.2 Purpose The purpose of this report is to describe the results of the slope stability analyses, for Lake A, performed as part of the permitting requirements for Eliot Quarry. 2. SLOPE STABILITY ANALYSES 2.1 Lake A Slope Stability Analyses A total of four profiles were constructed and analyzed, Profiles A-D, Figure 2. Worst case scenarios were modeled, with the pit being completely empty and the slopes fully saturated with groundwater. For the seismic analyses, a seismic coefficient of 0.21 was used, as described in Section 4.5 of the Geotechnical Characterization Report. This coefficient value is considered quite conservative, or protective of surrounding properties, as discussed in more detail in the Geotechnical Characterization Report. Material properties are given in Table 1. Figure 2. Overview of Lake A cross section profiles

9 Page Geologic Model Following a review of available materials and a geotechnical investigation, a geologic model was constructed by KANE GeoTech. This geologic model shows the Livermore Valley s depositional environment being an alluvial system rather than the lacustrine deposit as proposed by CSA. The difference is an alluvial environment would result in discontinuous layers and a lacustrine environment has laterally continuous layers. KANE GeoTech conservatively modeled areas with continuous layers where drilling logs were unable to show otherwise to reflect CSA s geologic model. Borings locations are shown in the Geotechnical Characterization Appendix document. Material parameters for each profile are found in Table Lake A, Profile A. Data from three borelogs were used in the construction of Profile A. These borelogs show the discontinuity of the layers on the northern area of Profile A Lake A, Profile B. Data from five borelogs were used in the construction of Profile B. These borelogs also show layers of discontinuity throughout the Profile area Lake A, Profile C. Data from two borelogs were used in the construction of Profile C. These borelogs also reflect discontinuous layers in the northern area of the Profile. Due to the lack of data in the center of the Lake A in this area, the discontinuous layers were conservatively modeled to continue half way between the borelogs Lake A, Profile D. Data from three borelogs were used in the construction of Profile D. These borelogs show discontinuity in the northern area as well. Due to the lack of data in the center of Lake A, the low TABLE 1: TYPICAL MATERIAL PARAMETERS USED IN THE ANALYSES Profile Material Parameters Avg. Unit Weight (pcf) Saturated Unit Weight (pcf) Cohesion (psf) Friction Angle (Deg) A, B, C, D Clayey Gravel A, B, C, D Low Plasticity Clay B, C Low Plasticity Silt A, B, C, D High Plasticity Clay B Well Graded Sand B Pea Gravel Fill A, D Sheared Clay, high plasticity

10 Page 4 plasticity clay layers were conservatively modeled as continuous layers with a change in elevation, although, it is most likely the elevation change is due to the layers being discontinuous. 2.3 Lake A Slope Stability Results The analyzed profiles and results of the static and seismic slope stability analyses for Lake A can be found in Figure 2, Table 2, and Appendix A. Four profiles throughout Lake A were modeled and analyzed statically and seismically at various mining elevations with a 2H:1V slope gradient. Subsequent to the initiation of this investigation, CEMEX determined that Lake A will no longer be mined to the originally proposed elevations. Analyses showed that the slopes in Lake A are stable under static conditions. Profiles A, B, and C, Appendix A, are stable in both static and seismic conditions. The analyses of Profile D indicated that the slopes were stable under static conditions, but when modeled under seismic conditions the resulting safety factor of 0.98 did not meet the required value of 1.0 at the proposed pit depth, Appendix D; however under the revised grading plan the safety factor increased to 1.02, Appendix E. The slope was re-analyzed with a TABLE 2. SLOPE STABILITY ANALYSES RESULTS Lake A Profile A - Filled with Water Circular Failure SE Slope Circular Failure NW Slope Block Failure SE Slope Block Failure NW Slope FOS (Static) FOS (Seismic) Lake A Profile B -Filled with Water Circular Failure SE Slope Circular Failure NW Slope Block Failure SE Slope Block Failure NW Slope FOS (Static) FOS (Seismic) Lake A Profile C - Filled with Water Circular Failure SE Slope Circular Failure NW Slope Block Failure SE Slope Block Failure NW Slope FOS (Static) FOS (Seismic) Lake A Profile D - Filled with Water (as is) Circular Failure NW Slope Circular Failure SE Slope Block Failure SE Slope Block Failure NW Slope FOS (Static) FOS (Seismic)* *See text, Section 2.3

11 Page 5 new, proposed grading profile which modeled the slope as stable under seismic conditions. The grading profile can also be found in Appendix E. Profile A, located on the west slope adjacent to Isabel Avenue, was analyzed and modeled with a pit elevation of 360-ft MSL. This slope is the proposed location of the conveyance pipe that will link Lake A to the planned chain of lakes. The slope met the required safety factors and is considered stable when excavated to 360-ft MSL. 3. CONCLUSIONS AND RECOMMENDATIONS After performing the static and seismic slope stability analyses for Lake A, our conclusions are as follows: 1. It has been determined that Lake A will no longer be mined. The slopes were modeled under currently existing configurations, and all were stable statically and seismically with the exception of Profile D under seismic conditions. This slope was reanalyzed with a new grading plan and modeled stable under seismic conditions. The slope where the proposed conveyance pipe is located was modeled at the conveyance pipe elevation 360-ft MSL and was stable statically and seismically. 2. Elastic rebound of the slopes after mining should be expected. It should be noted that CSA (2009) stated that elastic rebound of Lake A slopes had occurred due to stress relief. Modeling conducted for this study shows that all slopes are stable, including those adjacent to the corrective action area (i.e. pea gravel buttress). 3. The sheared clay layer found in Lake A boreholes is not continuous. CSA s geologic model showed that the weak sheared clay layer is continuous. However based on observations made from KANE GeoTech s 2013 borelogs the sheared clay layer is not ubiquitous at Lake A. 4. REFERENCE Cotton, Shires, & Associates, Inc. (2009). As-Built Report and Summary of Construction Inspection and Testing, Lakeside Circle Corrective Action Plan,. Report to CEMEX, Eldorado Hills, California by Cotton, Shires, and Associates, Inc., Los Gatos, California, December 23, LIMITATIONS The analyses, conclusions and recommendations contained in this report are based on the site conditions observed by KANE GeoTech and derived from the information provided. If there is a substantial lapse of time between the submission of this report and the start of any work at the site, or field conditions have changed due to natural causes, mining, or construction operations at or adjacent to the site, we urge that this report be reviewed to determine the applicability of the conclusions and recommendations considering the changed conditions and time lapse. This report is applicable only for the project and sites studied. After three years, KANE GeoTech should be consulted if this report is used to make any decisions regarding the area.

Page 6 Our professional services were performed, our findings obtained, and our recommendations proposed in accordance with generally accepted engineering principles and practices.

12 Page 6 Our professional services were performed, our findings obtained, and our recommendations proposed in accordance with generally accepted engineering principles and practices. This warranty is in lieu of all other warranties either expressed or implied. Findings and statements of professional opinion do not constitute a guarantee or warranty, expressed or implied. William F. Kane, PhD, PE President California Registered Civil Engineer No

13 Page 7 APPENDIX A Slope Stability Analysis Profile A

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15 Page 9 Static Analysis

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23 Page 17 Seismic Analysis

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29 Page 23 APPENDIX B Slope Stability Analysis Profile B

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45 Page 39 APPENDIX C Slope Stability Analysis Profile C

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63 Page 57 APPENDIX D Slope Stability Analysis Profile D

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65 Page 59 Static Analysis

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83 Page 77 APPENDIX E Slope Stability Analysis Profile D (After Grading)

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CEMEX Eliot Quarry. Geotechnical Characterization Report. Alameda County, California

CEMEX Eliot Quarry. Geotechnical Characterization Report. Alameda County, California May 7, 2015 May 7, 2015 Project No. GT13-16 Prepared for: CEMEX 5180 Golden Foothills, Parkway El Dorado Hills, California 95762 7400 Shoreline Drive, Ste. 6 Stockton, California 95219 Tel: 209-472-1822