Three-dimensional observations of meso-structural changes in bimsoil using X-ray computed tomography (CT) under triaxial compression

In situ quantification of the meso-structural changes in block-in-matrix-soils (bimsoil) is crucial to the stability prediction of construction and building structures made of bimsoil. While the macroscopic failure of bimsoil has been widely studied, the physical meso-scale mechanisms governing bimsoil deformation have not been well understood. Here, high energy X-ray computed tomography (CT) measurements were performed on a bimsoil sample with rock block percentage (RBP) of 30% under triaxial compression, in order to collect three dimensional data on rock blocks and crack distribution. The 3D meso-structural changes have been visualized in real-time during triaxial deformation. The results showed that cracks propagated by passing rock blocks, leading to a macroscopic fracture with well-developed tortuous. In addition, interlocking occurs during the propagation of cracks, and the 3D pattern of the macroscopic fracture surface has been revealed from the reconstructed CT volume data. Moreover, rock-soil interface slippage, large pore formation, crack interlocking and growth together lead to formation of localization deformation. The localization deformation becomes obvious as axial strain grows, which can be reflected by the increasing 3D fractal dimension of the sample density distribution. This demonstrates the large control of local mechanical variations on the crack propagation in bimsoil, which is caused by existing rock blocks on. Through a series of meso-structural evolution analysis, the meso-mechanisms of localized deformation for bimsoil under triaxial deformation have been first documented. (C) 2018 Elsevier Ltd. All rights reserved.