Triaxial Behaviour of Layered Soil at Small Strain Level

Abstract

The purpose of this study was to analyze the anisotropic behaviour of layered soil at small strain level. This thesis comprised experimental, numerical, and theoretical aspects and provided an insight to the concept of the ‘equivalent’ homogeneous cross-anisotropic material indicating that the layered soil can be replaced by an equivalent transversely isotropic material under certain conditions. In the experimental program, this study extended Vaid’s work (1971) to conduct K0-compression tests in a rigid triaxial cell with a flexible lateral boundary for the determination of the K0-value of normally consolidated soil. The error induced by the compliance of the cell-water system that always existed in the previous study was successively eliminated by attaching a compliance correction system (i.e., GDS controller) to the triaxial cell. Three stress path tests (i.e., the K0-compression test, the plane strain compression test, and the hydrostatic pressure compression test) were conducted consecutively in a rigid triaxial cell for a layered soil specimen to determine the elastic cross-anisotropic properties of the equivalent homogeneous material. The applicability of the proposed approach was demonstrated by conducting the tests on two types of soil (i.e., the homogeneous soil and the layered soil). A three-parameter constitutive equation for describing the soil’s cross-anisotropic elastic behaviour was modified in a basic FEM program. Based on the material properties determined by the experimental study as an input, numerical simulations (i.e., the numerical K0-test) using FEM were conducted to compare numerical results with the test results. In the theoretical part, this study made use of the Reuss and the Voigt approximations and proposed a simple, yet physically meaningful, approach to determine the equivalent cross-anisotropic elastic properties of a multilayered medium. To simplify the exposition, a multilayered medium with two constituent materials that were both isotropic was examined.