Study on cross-scale fractal law of disintegration and failure of water-bearing mudstone under different stress paths

In order to study the disintegration evolution characteristics of mudstone under water and different stress paths，scanning electron microscopy，high-energy CT and triaxial servo press were used to explore the fractal dimension variation law of microscopic particle structure，microscopic pore number，macroscopic disintegration and failure fragmentation，and reveal the cross-scale failure mechanism of mudstone. The results show that：(1) The particle size and morphology of pyrite and kaolinite in mudstone are different，and the primary pores will become water seepage channels. With the increase of water content，the deterioration of kaolinite structure leads to the widening of water seepage channel and the increase of microscopic pore fractal dimension. (2) The number of large pores increases and penetrates，and natural disintegration of mudstone occurs. The fractal dimension of disintegration block is between 1.26 and 1.77，which is larger than that of pore fractal dimension. The damage fragmentation fractal under loading and unloading is greater than that under natural disintegration，reflecting the damage superposition effect of external force. (3) The fractal dimension of fragmentation under loading and unloading is all partitioned. Before the characteristic water content，the fractal dimension of the block is negatively correlated with the strength，but it is positively correlated with the strength after exceeding the characteristic water content. The inflection point of the fractal dimension can be used as the demarcation point of the influence of water content and stress. At this point，the influence of water on the main fracture surface reaches the peak. (4) The unloading stress path affects the failure characteristics and morphology of water-bearing mudstone. The low-water-content mudstone exhibits brittle failure，and the high-water-content mudstone exhibits plastic failure. The tensile failure increases，and the fragments are mostly“flaky”. © 2023 Academia Sinica. All rights reserved.