Anisotropic Behavior of Cohesive Soils by Considering Effect of Gradation and Plasticity Characteristics

Abstract

In practice, strength of soils commonly is measured isotropically, while for accurate design of structure foundations and earth structures, it is essential to consider the effect of anisotropy phenomenon on the mechanical behavior of the soils. In previous research, the effect of anisotropy on shear strength of sandy soils has been known and there is some limited work on cohesive soil. Moreover, anisotropy impact is not known on shear-induced pore water pressure. In this research, a series of triaxial tests were carried out on the undisturbed samples of different fine-grained soils, taken at different directions in the sites. The samples were consolidated under effective isotropic stresses of 200, 300, 500 and 700 kPa, and loaded in undrained condition. The results revealed that the behavior of all soils significantly depends on the sample orientation in the field. As the direction of samples changed from “perpendicular to bedding orientation” to “parallel to bedding orientation”, the shear strength decreased gradually and it has the minimum value at anisotropy angle of 72°, 59° and 90° for red clay, yellow marl and olive marl, respectively. The reduction rate completely depends on the soil plasticity and level of confining pressure.