On the kinematics of shelly carbonate sand using X-ray micro tomography

Abstract

Shelly carbonate sands are highly compressible soils due to the susceptibility of their loose and intricate fabric to collapse under loading. An accurate assessment of the physical phenomena taking place at the grain-scale is critical for a better understanding and modelling the mechanical behaviour of this material. This paper presents a study on the grain kinematics of shelly carbonate sand through analysis of in-situ 4D X-ray tomography images acquired during oedometer compression. Two sands from the Persian Gulf, with coarse and fine grading, were investigated. An adaptive watershed segmentation technique is used here to identify the grains in the image(s) prior to loading and a digital volume correlation (DVC) technique is employed to obtain the displacement field of each grain under loading. The displacement fields are used to reconstruct the grains in their new positions and compute the associated translation and rotation. An extensive statistical analysis was carried out to demonstrate the effect of grain morphology and local fabric (coordination number) on grain kinematics. The new findings presented here shed light on the mechanisms of grain rearrangement leading to the compressible fabric of shelly carbonate sands and, are also critical, to better understand other weak grained sands and/or silica sands with an open fabric.