Evolution of particle breakage of calcareous sand under large displacement shearing

To reveal breakage behavior and deformation of particle shape for calcareous sand from the South China Sea with large shearing displacement, a series of ring shear tests was performed under controlled shear displacement. After ring shear, the particle size distributions of the samples were obtained by the sieving method and laser grain-size analyzer. The particle breakage was quantitatively examined by analyzing particle size distribution. The roundness and flatness was also analyzed to examine the variation of particle shape using the image processing technology. Experimental results indicate that shearing under different vertical pressures would lead to different stable graduations. However, the stable graduation is observed under the same shearing displacement. Severe breakage occurs in the samples with particle sizes of 0.01-0.075 mm after large displacement shearing. With the increase of the shear displacement, the roundness and the flatness of particles decrease. The relative breakage is modified to account for the severe breakage of fine grains (<0.075 mm) in large displacement shearing. The modified relative breakage ratio can cover the breakage of the particles with sizes of 0.01-0.075 mm. After large displacement shear, the shape of calcareous sand tends to be more regular, more rounded and smoother.