Model Prediction of Anisotropic Behavior of Boston Blue Clay

Abstract

This paper investigates predictive capabilities of the effective stress soil model MIT‐E3 (described in a companion paper) through detailed comparisons with laboratory test data for Boston blue clay (BBC). The main focus of these evaluations is predictions of anisotropic stress‐strain behavior using data from two special laboratory shear devices: the directional shear cell (DSC), and the multi‐directional direct simple shear apparatus (MDSS). Input parameters are first estimated from standard types of laboratory data, including one‐dimensional (K0) compression and undrained triaxial shear tests. The DSC is a plane strain apparatus with the additional capability of controlling principal stress directions during shear. Measurements in this device include undrained shear tests with principal stress rotations at OCR=1, and with fixed stress direction but different principal stress orientation at OCR=4. The MIT‐E3 model describes accurately the observed variations in undrained shear strength and stress‐strain behavior in tests at OCR=1, but is notably less reliable at OCR=4. The MDSS has the same dimensions and boundary conditions as the Geonor simple shear apparatus, but can apply horizontal shear stresses in two independent directions. Measurements in the MDSS apparatus demonstrate the anisotropic properties of BBC at OCR=1 induced by consolidation under an applied shear stress. MIT‐E3 predictions are in excellent agreement with measured variations in peak shear resistance and prepeak stress‐strain response.