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Title: Engineering properties of clay shales. Report 4, Laboratory and computational procedures for predictions of pore pressures in clay shale foundations
Authors: Soils and Pavements Laboratory (U.S.)
Leavell, Daniel A.
Peters, John F.
Townsend, Frank C.
Keywords: Clay shales
Pore pressure
Soil tests
Soil testing
Soil mechanics
Publisher: Geotechnical Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: 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. Two methods were developed to compute pore pressure caused by embankment loads. The first method was implemented in the computer code CURLS and was used to predict foundation pore pressures for a Corps of Engineers dam. The second method consists of graphical construction of an influence chart and is intended for rapid field estimates of pore pressures. Both methods were shown to give a good estimate of instantaneous pore pressures. However, rapid redistribution of pore pressures during consolidation was shown to be significant, especially near embankment boundaries where pressures may be several times greater than those predicted.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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