Strain localisation characteristics in sandstone during uniaxial compression by 3D digital image correlation

A series of monotonic uniaxial compression tests under quasi-static loading conditions on Hawkesbury sandstone specimens were conducted. To accurately measure pre-peak and post-peak stress-strain behaviour, lateral strain-controlled test at a prescribed constant loading rate were undertaken. To study localised deformations of specimen, 3D Digital Image Correlation (DIC) technique was used. 3D DIC is a non-contacting optical method for strain measurement that uses two-digital cameras to acquire images of the undeformed and deformed shape of an object. Field of strains and strain localisation in the rock surface were analysed by 3D DIC method and coupled with the respective stress levels applied to the rock. By using 3D DIC technique relatively large strains developed in the post-peak regime within localised zones were accurately measured. Field strain development in the rock samples suggests that strain localisation takes place progressively and develops at a lower rate in pre-peak regime, otherwise it is accelerated in post-peak regime associated with the increasing rate of strength degradation. The results show that a major shear failure plane, due to strain localisation, becomes noticeable only long after peak stress.