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.

本研究通过三轴剪切试验与CT扫描试验，探究了渗流作用下炭质泥岩的力学特性与微观结构演化规律。采用Avizo 3D提取微观结构参数，并通过灰度关联分析量化其对抗剪强度的影响。结果显示：抗剪强度随岩石含量升高先升后降；渗流前抗剪强度峰值出现在岩石含量为60%的试样中，渗流后峰值则对应40%岩石含量。渗流后，炭质泥岩试样的内聚力均出现不同程度的劣化，其中岩石含量为60%的试样降幅最大，达28.7%。随着渗流过程持续进行，试样内部细颗粒不断发生流失，该现象在粗、细颗粒的接触区域尤为显著。五组不同岩石含量的炭质泥岩试样的三维孔隙度分别提升了4.10%、2.46%、1.63%、9.36%与13.36%。依据渗流侵蚀演化机制，微观结构演化对力学性能的劣化过程具有显著影响。灰度关联分析结果表明，微观结构特征参数与抗剪强度参数（即内聚力、内摩擦角）之间的关联度均高于0.65。