Estimation of intact undrained shear strength of clay using full-flow penetrometers

Abstract

Full-flow penetrometers, Ball and T-bar, have been widely used to measure the undrained shear strength of offshore clayey soils in both laboratory and in situ tests. The penetration process of Ball or T-bar penetrometer is a large deformation geotechnical problem, which results in the surrounding soil partially remolding and softening. The soil disturbance influences the penetration resistance and hence leads to an underestimation of the undrained shear strength, which is a critical factor for offshore geotechnical design. To investigate the soil strain-softening behavior during the first penetration, large deformation finite element (LDFE) analyses were performed to simulate the penetration process of T-bar and Ball in the strain-softening clay. The thin layer element was employed to simulate the complex contact behavior between the penetrometer and the surrounding soil, thus the strain-softening behavior can be considered at the interface between penetrometer and soil. This study aims to investigate the effects of soil strain-softening and interface roughness on the penetration resistance during the first penetration of full-flow penetrometers. Based on the numerical results, relative comprehensive formulas considering the soil strain-softening parameters and the interface roughness factor have been proposed to evaluate the strain-softening factors, which can be used to estimate the soil intact undrained shear strength and the strain-softening parameters. Finally, the proposed formulas were verified by experimental results and were used to estimate the intact undrained strength of soft clay.