An investigation into the effects of block size on the mechanical behaviors of bimsoils using variable-angle shear experiments

Abstract

Shear resistance is critical to the stability of bimsoils (block-in-matrix soils), although the shear mechanical behaviors of bimsoil have been widely studied, the effect of rock block size on the rock–soil interactions, block occlusion and the interlocking effect during shearing are still not well understood. This work aims to investigate the effect of block size on the macro–meso shear failure mechanism of bimsoils using a specially designed variable-angle shear testing. Compaction test with different hammer counts was used to prepare the bimsoil samples having different rock block proportions and sizes, to roughly ensure the same compactness of soil matrix. Macroscopic shear force–displacement analysis combined with the mesoscopic 3-D laser technique was used to reveal the internal shear failure mechanism. The results show that block size has obvious effect on the shear strength parameters and morphology of shear failure plane. The peak shear force increases with the increase of block size, and the occlusion and interlocking phenomena become severe for the sample with relatively large block size. An index of fractal dimension was used to establish the relationship between block size and shear strength parameters, it suggests that the fractal dimension of the fracture surface is large for the samples having larger block size, and the shear strength of bimsoil is strongly related to the morphology of fracture surface. The improvement of shear strength for bimsoil was the results of interactions between soil matrix and rock blocks and induced by the intrinsic shear fracture mechanism.