Engineering Properties of Clay Shales. Report 5. Strength and Deformation Properties of Pepper and Del Rio Clay Shales from Waco Dam

摘要

The investigation was conducted for the purpose of determining the effect of current (1962-1969) standard soil testing techniques on the shear strength of clay shales. The effects of variations in the rate of strain, specimen size, and length of shear path in the direct shear tests were studied. Results indicate that the shear strength increases as the specimen thickness and the rate of strain decreases. Consolidation tests results show no effects from use of different inundation liquids, no evidence of structural collapse, and no differences in side friction under various ring preparations. Values of t50 and expansion pressures were different for the specimens of various thicknesses, but causes of these differences are not apparent. Results of triaxial compression tests indicate a significant amount of negative pore pressure in the laboratory specimens. It must be assumed that the negative pore pressure developed after the samples were obtained since the materials in situ exhibited pores pressures in excess of the ground-water table. The variation in physical properties of the indisturbed test specimens, such as density, water content, plasticity, and structure, contributed appreciably to variations in all test results. Results of this study indicate the need for new test procedures and equipment to determine the shear strength characteristics of clay shales. Additional research is required to develop the most applicable techniques.