Effect of directional stress history on anisotropy of initial stiffness of cohesive soils measured by bender element tests

Abstract

This paper describes the initial stiffness of reconstituted kaolinite clay in both vertical and horizontal planes under three different stress histories. The initial shear stiffness was obtained from bi-directional bender element tests during isotropic and K 0 stress loading and unloading. An empirical correlation was established based on the initial stiffness of normally consolidated soils. Unlike the unique relationship of the initial vertical stiffness of normally consolidated clays, the initial stiffness in the horizontal plane is dependent on the stress ratio and previous stress history; thus, three different relationships of the initial horizontal stiffness were obtained for the three loading programs. The effect of the stress history on the initial horizontal stiffness can be considered properly by defining the degree of overconsolidation in terms of the horizontal effective stress. The change in the initial stiffness has a directional dependency on the stress history in the direction of the particle motion and wave propagation in the bender element tests.