Date of Award

Spring 1977

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Raj P. Khera

Second Advisor

William J. Stack

Third Advisor

Eugene B. Golub

Abstract

The cause and the nature of anisotropy in a cohesive soil was investigated by direct shear and triaxial compression tests. Laboratory techniques and procedures used to prepare isotropic clay samples are given where consolidation was accomplished under hydrostatic pressure. Direct shear tests were performed on these specimens trimmed at different inclinations to the physical horizontal from the block samples. The ratio of undrained shear strengths in any direction to shear strength in the vertical direction was found to be equal to one, proving isotropy existed. Similar tests were performed on specimens trimmed from the same clay consolidated one-dimensionally. Results from these tests showed the shear strength ratio to be maximum for specimens trimmed at 90° to the horizontal plane. In this case, the aniso- tropic characteristics were directly attributed to the sample stress history. These samples indicated preferred particle orientation. Undrained triaxial compression tests were performed on both hydrostatic and one-dimensionally consolidated samples. Triaxial test results confirmed the results of the direct shear tests and more accurately defined the stress/strength parameters. The angle between the failure plane and the test specimens axis was essentially constant and the ratio between pore water pressure at failure and the mean consolidation stress remained a constant.For each maximum consolidation stress, pore pressure was isotropic, but in all cases was higher for hydrostatically prepared samples. The hydrostatic method of preparing isotropic test specimens was effective and produced reliable results.

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