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L <br />' B. PROPERTIES OF FOUNDATION MATERIALS <br />Soil borings were located over a large area of the property owned by Colowyo <br />' Coal Company, and seem to indicate a fairly consistent pattern of approxi- <br />mately 5 to 10 feet of residual soil which was most likely weathered in <br />' place from the underlyir~ parent shales and sandstone. The materials typi- <br />cally classify as moderate to highly plastic clay (CH or CL) according to the <br />Unified Soil Classification System. Typical gradation curves and a summary <br />of the Atterberg Limits fot these soils are presented in Appendix B. A <br />' summary sheet of specific gravities, water contents and dry densities for <br />several of the samples tested is also presented in Appendix B. A consider- <br />able range in properties is to be expected for these soils, depending pri- <br />' warily on the rock type, amount of weathering, and the environmental con- <br />ditions under which weathering has occurred. Therefore, within any bore <br />' hole, and across the site, the soil will have variations in water content, <br />dry density, and strength characteristics. The samples selected for test- <br />' ing cover this range of properties, thus average values can be determined <br />for design purposes. <br />1 Triaxial tests were performed on representative samples in order to establish <br />' the total and effective stress shear strength parameters for use in stability <br />analyses. A summary of the effective stress strength parameters, as determined <br />from isotropically consolidated-undrained (ICU) triaxial tests is shown on <br />' Figure III-1 in the form of stress paths. Another convenient method of <br />showing the results of those tests, in order to evaluate the increase in <br />' undrained shear strength due to consolidation, is to plot the undrained <br />shear strength, Su, versus the effective confining pressure, ac', as shown <br />in Figure III-2. Figure III-3 shows a summary of the unconsolidated-undrained <br />(UU) triaxial tes[s used in determining the in-situ total stress strength <br />' parameters. <br />Three quick direct shear tests were also performed to identify the transi- <br />t tion of materials from topsoil into the "partly weathered" zone located <br />above the intact rock. Results of those tests are presented in Appendix B. <br />Actual strength parameters used in design are shown on the figures in Appendix <br />' C for the various stability analyses performed. <br />WaWRHLER Project 0823 III-2 <br />& ASSOCIQi6 <br />