ANISOTROPY AND STRESS PATH EFFECTS IN CLAYS

NAGARATNAM SIVAKUGAN, Purdue University

Abstract

Anisotropy and stress path are two major factors requiring attention in laboratory and in situ testing. In the research reported herein, experimental and theoretical studies were made on these two factors. Experiments were performed in a servo-controlled cuboidal shear device, and analytical studies were based on the Cam Clay and the modified Cam Clay models. When implications of the findings made in this dissertation are discussed, emphasis is given to pressuremeter testing where anisotropy and stress path play a role. However, the results are of a general nature, and apply to other problems as well. Stress anisotropy in consolidation was studied analytically. A simple procedure was developed to predict the in situ or K$\sb{\rm o}$ undrained shear strength from the results of ordinary CIUC tests. The procedure was validated with published experimental data on 24 different soils. To model the in situ behavior of clays, the critical state models, Cam Clay and modified Cam Clay models, were extended to consider the K$\sb{\rm o}$ consolidated initial state. A new state parameter, spacing ratio, was introduced to simplify the analysis. Expressions were developed for undrained shear strength and for Skempton's A-parameter at failure. Plane strain conditions are often assumed in the interpretation of pressuremeter test results in clays. Variation of principal stresses during plane strain compression were studied using the modified Cam Clay model. It was shown that $\sigma\sbsp{2}{\prime}/(\sigma\sbsp{1}{\prime} + \sigma\sbsp{3}{\prime})$ steadily increases, but only slightly, during plane strain compression, which is in agreement with previous experimental results. For practical purposes it is a good approximation to assume that $\sigma\sbsp{2}{\prime}/(\sigma\sbsp{1}{\prime} + \sigma\sbsp{3}{\prime})$ is a constant throughout plane strain compression loading. A cuboidal shear device with automatic data acquisition system and servo control, a slurry consolidometer, and appurtenent components were developed. Isotropically or anisotropically consolidated cubical specimens were loaded horizontally or vertically under undrained conditions. A significantly larger $\phi\sp{\prime}$ was observed when the loading was horizontal in direction. Thus, in practice it is necessary to use the value of $\phi\sp{\prime}$ appropriate to the direction of field loading.

Degree

Ph.D.

Subject Area

Civil engineering

COinS