EXPERIMENTAL RESEARCH ON DEVELOPMENT/DIMINISHING OF ANISOTROPY AND ITS EFFECT ON MECHANICAL BEHAVIOR OF CLAY

Abstract

Anisotropy refers to the directional dependence of material properties. The knowledge of
development/diminishing of anisotropy are very important, to understand the true behavior of naturally deposited
soil. The anisotropy of clays and silty clay intimately connected with their structure, which depends on the
environmental conditions during which the soil is deposited as well as the stress changes subsequent to
deposition. In this paper, triaxial tests were carried out using the vertical and the horizontal extraction specimen
of the reconstituted clay and silty clay, for accumulating experimental facts of development of anisotropy during
the preliminary consolidation process and the influence of the anisotropy on the shear behavior. Preconsolidation pressure of 200kPa applied to induced initial anisotropy. Undrained shear triaxial test was
performed with different isotropic stresses on clay (50 to 1800kPa) and silty clay (50,300 and 600kPa), and
undrained shearing was carried out under constant axial strain rate of 0.0056(mm/min). Vertical sample shows
larger peak strength as compared to horizontal, because of the development of anisotropy on the compression
side. As the confining pressure increases, the difference between peak strength of vertical and horizontal
becomes smaller and smaller which indicate that the anisotropy diminished and intensity ratio decreases. By
comparing clay and silty clay, silty clay materials lose their anisotropy at lower confining pressure (600kPa) as
compared to clay materials (1800kPa). Therefore, the grain sizes have significant effect on the developing and
diminishing of anisotropy. Another important fact observed was, critical state index is decreasing and becomes
constant as confining pressure increases.