Micro-structural Evolution of Granite Residual Soil under External Loading Based on X-ray Micro-computed Tomography

As a completed decomposed product of granite rock, the granite residual soil widely distributes in South China with a special soil structure that can be easily damaged under external disturbance. Therefore, studying the evolution of soil cracks during the loading process is important for engineering practice that needs to evaluate the soil shear strength, such as slope stability analysis. The purpose of this study is to investigate the micro-structure for the intact granite residual soil under external loading base on X-ray computed tomography (CT) through global and local scanning (with resolutions of 180 µm and 26.7 µm, respectively). The micro-structural evolution of the cross-sections of soil column extracted from a granite residual soil layer under axial loading was investigated by CT scanning with a 0.5 mm slice thickness. The number of cracks (including macro-cracks and meso-cracks), area ratios and porosity corresponding to varying loading stages (initial, peak-stress and failure) were analyzed based on the cross-sectional CT images. Test results shows that the structure strength of the soil was mainly subject to macro-cracks. In addition, the increase of the porosity is mainly attributed to the generation and expansion of the cracks along sandy particle under external loading. This study can provide theoretical support and data support for understanding the micro-structural evolution of granite residual soil that is commonly encountered in civil engineering.