Mechanical properties and microstructural evolution of carbonaceous mudstone under seepage conditions

The mechanical properties and microstructural evolution of carbonaceous mudstone under seepage were investigated through triaxial shear and CT scanning tests. Microstructural parameters were extracted using Avizo 3D, and grayscale correlation analysis was performed to quantify their influence on shear strength. The results show that the shear strength increases and then decreases with increasing rock content, reaching a maximum of 60% rock content before seepage and 40% after seepage. The internal cohesion of carbonaceous mudstone specimens after seepage was reduced to different degrees, with a maximum reduction of 28.7% for the specimen with 60% rock content. The loss of fine grains inside the specimen occurs continuously as the seepage process proceeds, especially in the contact areas between coarse and fine grains. The increase in 3D porosity of the five groups of carbonaceous mudstone specimens with different rock content was 4.10%, 2.46%, 1.63%, 9.36%, and 13.36%, respectively. According to the evolution mechanism of seepage erosion, microstructural evolution significantly affects the deterioration process of mechanical properties. Grayscale correlation analysis revealed that the correlation between microstructural characteristic parameters and shear strength parameters (i.e., cohesion, internal friction angle) was above 0.65.