2004-02-24_REVISION - M1977153 (4)

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Geotechnical Data Technical Memorandum Hazeltine -Road Runners Rest II Gravel Pit Lining Project December 2000 4.4.2 Phase Two Testing Based on the results of the Phase One tests and estimated quantities of materials at each potential source sampled during Phase One, additional laboratory tests were performed on samples of the claystone bedrock from the bottom of the Hazeltine Pit and samples from the overburden stockpile at the Howe-Haller Pit. Additional tests were not performed on samples of the stockpiled material at the Hazeltine Pit, because available quantities were estimated to represent less than 10 percent of the material required to construct the pit side slopes. Additional tests were not performed on the materials from the tailings ponds because, based on the data from the index tests and visual observations, it was determined that this material would not have the strength, compaction, and permeability properties desired for a low permeable liner or for the reservoir side slopes. The three samples taken from the Howe-Haller Pit overburden stockpile were combined into one composite sample. Tests performed on the composite sample included sieve analyses, Atterberg Limits, Standard Proctor, back pressure hydraulic conductivity, and consolidated- undrained triaxial with pore pressure measurements. A consolidated-undrained triaxial shear test with pore pressure measurements and a back pressure hydraulic conductivity test were performed on a sample of bedrock from the bottom of the Hazeltine Pit. Test results for the Phase Two Program are provided in Appendix E and summarized in Table 4.8. Effective and total stress failure envelopes for the remolded Howe-Haller overburden stockpile samples are provided on Figures 4.1.1 and 4.1.2, respectively. Effective and total stress failure envelopes for the remolded bedrock samples are provided on Figures 4.2.1 and 4.2.2, respectively. The triaxial and permeability test specimens were prepared by moisture conditioning the material to within about 1 to 2 percent above optimum moisture content and then compacting the remolded material to about 95 percent of its Standard Proctor maximum dry density. For the triaxial tests, the remolded specimens were consolidated at the appropriate confining pressure and then tested in axial compression, which was accomplished by increasing the axial load on the specimen. The specimens were generally loaded until axial strain was about 20 percent. For the permeability tests, the specimens were saturated then consolidated at a confining pressure of about 1580 psf. Permeability tests were performed at an average effective stress of about 11 psi, which is the difference between the cell pressure and the back pressure. GEI Consultants, inc. 4_S ~~ u 98_'ISgeo tm»yC