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-13- • Pitcher type sampler was used in 78-38 to obtain 3-inch diameter relatively undisturbed samples of the more weathered sedimentary rocks. Several in- tervals were sampled and approximately 20 relatively good specimens were obtained for testing. The samples tested represent the softer material encountered in exploratory borings and, in our opinion, are representative of the lower strength materials which wil] occur in the pit wall slopes. To evaluate the shear strength of the softer materials, direct shear and triaxial shear tests were performed. The plane of shear is controlled by the testing machine in the direct shear test. The sample controls the plane of shear in the triaxial shear test. In most of the samples tested, the shear failure in the triaxial test occurred along pre-existing bedding planes. Samples were 3 inches in diameter and 6 inches long. Some of the samples were of sufficient length not to encounter bedding plane and shear occurred through relatively intact material in the triaxial test. Most of • the shear strengths observed from the triaxial test, in our opinion, re- present residual shear strengths. The residual shear strength is the strength available in the formation after considerable shear deformation has occurred, whether by loads imposed by the man-made operations or from previous geologic conditions. As a contrast, the shear strength obtained from the direct shear tests represent peak values. Values were obtained by shearing through rela- tively intact portions of the formation. Stress-strain diagrams and Mohrs diagrams for the results from the triaxial and direct shear testing are pre- sented in Appendix I. The results of the testing vary rather erratically and there were not sufficient samples available to conduct enough tests to develop a statistical evaluation of the strength. Triaxial shear test results •