Determination of depth-dependent undrained shear strength of structured marine clays based on large deformation finite element analysis of T-bar penetrations

Abstract

T-bar penetrometers are widely used for measuring the undrained shear strength profiles of soft clays in either laboratory 1 g and ng model tests or field investigations. In fact, natural marine clays are highly structured (with significant initial brittleness) and exhibit a depth-dependent increase in undrained strength, which greatly affects the T-bar penetration behavior. In this paper, the initial brittleness is taken into account by introducing a structural parameter in strain softening model. Large deformation finite element (LDFE) analysis of full-process T-bar penetrations in structured clays with depth-dependent undrained strength are conducted using coupled Eulerian–Lagrangian (CEL) approach. A comprehensive parametric analysis is performed to investigate the effect of each normalized strength parameter, strain rate parameter and softening parameter on the penetration resistance factor (N_T) of T-bar and correct N_T against the combined effect of them. Based on the LDFE/CEL results, a back-analysis framework for estimating the intact undrained shear strength profiles of natural marine clays is established. The corrected soil sensitivity and the softening and rate parameters of the clay are obtained as by-products of the back analysis. Finally, the reliability of the back-analysis framework is validated by LDFE/CEL results and the data from laboratory T-bar and vane shear tests.