Growth distribution laws and characterization methods of cracks of compact sandstone subjected to triaxial stress

A series of triaxial compressive tests and CT scanning tests on tight sand are carried out using the triaxial testing machine and CT scanning machine. The CT images of fractured cracks subjected to diverse triaxial stresses are obtained. The image processing technique and statistic principles are employed to extract geometric morphology of crack growth. The geometrical parameters are proposed to describe the growth morphology of fractured cracks, i.e., area, length, width and fractal dimension. The distribution characters of geometric parameters are analyzed. The effects of confined pressure on distribution characters of the above geometric parameters are exposed. The results show that the confined pressure has significant effects on the geometrical features of fractured cracks, such as area, length, width and fractal dimension. The area, length and width are all smaller when the confined pressure is smaller. With the increase of the confined pressure, the values of geometrical parameters rise also. The diverse confined pressures lead to different probability density distribution functions of geometrical parameters. The fractal dimensions of fractured cracks accord with the exponential decline law when the confined pressure rises. The fractal dimensions of cracks subjected to low confined pressure are larger than the ones subjected to high confined pressure. When the confined pressure is lower, the cracks with larger fractal dimensions exhibit complex geometric morphology and rough boundary curves. The crack networks with more small cracks occupy the whole cross section of specimens. When the confined pressure is higher, the cracks with less fractal dimensions become more regular and smooth. The main cracks approximating straight line appear and the small cracks disappear.