Mesoscopic measurement of damage and shear bands of granite residual soil using Micro-CT and digital volume correlation

Abstract

The mesomechanics of geotechnical materials are closely related to the macromechanical properties, especially the mesoscale evolution of shear bands, which is helpful for understanding the failure mechanism of geotechnical materials. However, there is lack of effective quantitative analysis method for the complex evolution mechanism of three- dimensional shear bands. In this work, we used X-ray computed tomography (CT) to reconstruct volume images and used the digital volume correlation (DVC) method to calculate the three-dimensional strain fields of granite residual soil samples at different loading stages. The trend of the failure surface of the shear bands was obtained by the planar fitting method, and the connectivity index was constructed according to the projection characteristics of the shear bands on the failure trend surface. The results support the following findings: the connectivity index of the shear band increases rapidly and then slowly with increasing axial strain, which is characterized by a near ‘S’ curve. As the stress reaches the peak value, the connectivity index of the shear bands almost exceeds 0.7. The contribution of the new shear band volume to the connectivity of the shear bands becomes increasingly small with increasing axial loading. Affected by quartz grains and stress at the initial stage, the dip angle gradually and finally approaches the included angle of the maximum shear stress from the discrete state with increasing axial loading. The tendency and dip angle of the resulting shear bands are dynamic, and the tendency slightly deflects with increasing loading.