Cavity expansion analysis of pile installation in chalk using synchrotron X-ray computed tomography

Abstract

Pile installation in chalk was investigated using physical models and in-situ synchrotron X-ray computed tomography. The aim was to quantify void ratio (e) changes in the chalk induced by pile penetration and assess the suitability of drained cavity expansion theory to predict these changes using a critical state model with plastic hardening and cementation degradation. Two experiments were carried out: a cone-tipped pile was slowly and monotonically pushed into the sample to model drained penetration, and an open-ended tube pile was cyclically jacked at a fast rate to mimic partially undrained pile driving. Cavity expansion analysis accurately predicted the remoulded chalk e values at the pile wall for both experiments. It also delivered accurate predictions of the radial e profiles of the remoulded zone, but accuracy slightly decreased for the partially undrained case. Radial e profile predictions for an exhumed field-scale pile from the literature yielded similar results. Analytical results were highly sensitive to the intact chalk density, which affected plastic hardening. The initial stiffness also affected results, but to a lesser degree. The cementation degradation rate had a negligible effect, as cementation strength was found to be small compared to stresses mobilised during plastic hardening.

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ORCID for Fernando Alvarez-Borges: orcid.org/0000-0002-6940-9918

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