Localised deformation in a wide-grained sand under triaxial compression revealed by X-ray tomography and digital image correlation

Understanding the mechanisms of deformation and failure of soils is essential in geotechnical engineering. In particular, strain localisation is a key issue for the failure of soils. In laboratory mechanical testing, localised deformation can be investigated efficiently through full-field measurements of displacement and strain in soil specimens. The objective of this study is to investigate the deformation and the failure of a soil under triaxial compression using in situ X-ray (i.e., X-ray scanning during the loading test) computed tomography (CT) and digital image correlation (DIC). This paper is concerned with the characterisation of internal strains and with strain localisation patterning in wide-grained sand undergoing triaxial compression at different confinement pressures using Three Dimensional (3D) volumetric DIC. Complete 3D images of specimens have been recorded at several stages throughout the triaxial tests and analysed using 3D volumetric DIC in order to obtain 3D incremental displacement and strain fields. Based on the results of the combined X-ray tomography and DIC, the deformation process and especially the strain localisation are quantitatively characterised in space and time under different triaxial compression conditions.