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

Abstract

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.

摘要

颗粒的接触方式以及颗粒的规则化处理对于研究岩土力学性质非常关键。本次研究中采集到了 广州及福建地区的花岗岩残积土, 在实验室条件下将其分别筛分成五种不同的粒组(d<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), 基于微观层析成像 技术研究颗粒之间的接触方式。利用主成分分析法对组成颗粒的体素进行识别和搜索, 确定颗粒的中 心、方向及尺寸; 基于笛卡尔空间坐标系, 根据相邻颗粒关键位置的空间坐标, 对其接触方式进行判 定。结果显示, 当花岗岩残积土颗粒粒径小于 0.2 mm 时, 颗粒接触方式主要包含面-面、面-角、面-棱、棱-棱、棱-角、角-角接触; 当颗粒粒径大于 0.2 mm 时, 颗粒接触方式主要包含面-面、面-角、面 -棱、棱-棱、棱-角、角-角、球-球、球-面、球-棱、球-角接触。土样的原始孔隙率、重建后的孔隙率 及规则化后的孔隙率三者之间存在差异, 这主要与花岗岩残积土遇水膨胀及崩解特性有关。