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 (PFEM). 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 localized 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 centerline than SPM. The results also show how including a beveled 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.

This work has been supported by the Ministry of Science and Innovation of Spain through research grant BIA2017-84752-R. The third author acknowledge financial support from the Spanish Ministry of Economy and Competitiveness, through the "Severo Ochoa Programme for Centres of Excellence in R&D" (CEX2018-000797-S)

Peer Reviewed

Postprint (author's final draft)