Determining the evolution characteristics of cracks and shear bands is important for understanding the damage mechanisms of geotechnical materials. However, there are few experimental studies on the mesoscopic evolution characteristics of cracks in shear bands. In this study, micro-chromatography (micro-CT) is used to evaluate the triaxial test processes of granite residual soil samples under confining pressures of 50 kPa, 100 kPa, 200 kPa and 300 kPa. Then, advanced digital volume correlation (DVC) is used to obtain three-dimensional strain fields and shear bands at different test loading stages, the evolution characteristics of cracks inside and outside the shear band are further measured basis on this. The results indicate that, if the maximum gradient region of the crack distribution in the initial state of the sample can form a trend surface similar to the “interface”, then the shear band may be generated in this region. After the formation of the shear band, the penetration degrees of the shear bands are similar to an curve with the increasing axial strain. The crack volume densities of the shear bands are obviously smaller than those of whole specimens. The crack volume densities on the shear bands first decrease rapidly and then increase gradually with increasing axial strain, and the increasing rate decreases with increasing confining pressure. Among the various crack types on the shear bands, the volume contents of brand-new cracks increase the fastest and exceed half, indirectly reflecting the severe deformation characteristics on the shear bands.

中文翻译：

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基于显微CT的先进数字体积相关法确定花岗岩残土剪切带的损伤演化特征

确定裂缝和剪切带的演化特征对于理解岩土材料的损伤机制具有重要意义。然而，关于剪切带裂纹细观演化特征的实验研究还很少。本研究采用微色谱（micro-CT）对花岗岩残余土样在50 kPa、100 kPa、200 kPa和300 kPa围压下的三轴试验过程进行了评价。然后，利用先进的数字体积相关（DVC）获得不同试验加载阶段的三维应变场和剪切带，在此基础上进一步测量剪切带内外裂纹的演化特征。结果表明，如果样品初始状态下裂纹分布的最大梯度区域能够形成类似于“界面”的趋势面，则该区域可能会产生剪切带。剪切带形成后，剪切带的穿透程度类似于随轴向应变增加的曲线。剪切带的裂纹体积密度明显小于整个试件的裂纹体积密度。随着轴向应变的增大，剪切带上的裂纹体积密度先快速减小，然后逐渐增大，且增大速率随着围压的增大而减小。在剪切带上的各种裂缝类型中，新生裂缝的体积含量增长最快，超过一半，间接反映了剪切带上的剧烈变形特征。