Engineering Properties of Clay Shales. Report 4. Laboratory and Computational Procedures for Predictions of Pore Pressures in Clay Shale Foundations

摘要

Design and stability analyses of structures founded on clay shales require knowledge of the pore pressure generated by applied loads. Since shales are anisotropic, heavily overconsolidated, and virtually impervious, high pore pressures can be developed that do not readily dissipate. Therefore, the objectives of this research were to (1) define the pore pressure and volume change characteristics of clay shales and (2) develop a technique for computing excess pore pressures in clay shale foundations. These objectives were successfully achieved by combined laboratory, analytical, and field investigations. The laboratory tests were performed on four clay shale specimens. All four specimens were anisotropic, with a stiffness of 1.3 to 2.5 times greater in the radial plane of the specimen than in the axial plane. Skempton's pore pressure theory was shown to give a good description of pore pressure response characteristics. By treating the shales as transversely isotropic materials, Skempton's pore pressure parameters could be related to the elastic constants. From theoretical consideration, Skempton's A parameter should fall within the range of 0.5 to 0.75. This range is consistent with the pore pressure response measured in the shales tested.