Use of X-ray computed tomography to study structures and particle contacts of granite residual soil

A small problem about soil particle regularization and contacts but essential to geotechnical engineering was studied. The soils sourced from Guangzhou and Xiamen were sieved into five different particle scale ranges (d< 0.075 mm, 0.075 mm≤d<0.1 mm, 0.1 mm≤d<0.2 mm, 0.2 mm≤d<0.5 mm and 0.5 mm≤d<1.0 mm) to study the structures and particle contacts of granite residual soil. The X-ray micro computed tomography method was used to reconstruct the microstructure of granite residual soil. The particle was identified and regularized using principal component analysis (PCA). The particle contacts and geometrical characteristics in 3D space were analyzed and summarized using statistical analyses. The results demonstrate that the main types of contact among the particles are face-face, face-angle, face-edge, edge-edge, edge-angle and angle-angle contacts for particle sizes less than 0.2 mm. When the particle sizes are greater than 0.2 mm, the contacts are effectively summarized as face-face, face-angle, face-edge, edge-edge, edge-angle, angle-angle, sphere-sphere, sphere-face, sphere-edge and sphere-angle contacts. The differences in porosity among the original sample, reconstructed sample and regularized sample are closely related to the water-swelling and water-disintegrable characteristics of granite residual soil.