Large-strain analysis of undrained smooth tube sampling

Abstract

Borehole tube sampling is a key process of geotechnical engineering. The paper presents numerical analyses of smooth tube sampling in clay using the particle finite-element method. The soil is described by a conventional elasto-plastic constitutive model (Tresca plasticity and a quasi-incompressible elastic law). The sampler is advanced by several diameters into the soil until a steady state is observed. The elasto-plastic numerical solution for a round-tipped sampler clearly identifies a localised shear failure mechanism at the entrance of the tube. Relevant strain path method (SPM) solutions are numerically evaluated to facilitate full field comparison. For a given thickness ratio elasto-plastic simulation predicts far less compression but much larger extensions at the centreline than SPM. The results also show how including a bevelled sampler tip or a stationary piston changes the failure mechanism and significantly reduces induced peak extension strains. The results agree with available experimental data and well-established empirical observations. The methodology presented may open the way to a soil mechanics-based rational approach to soil sampling simulation.