干湿循环作用下预崩解炭质泥岩强度特性及其劣化机制

Strength characteristics and deterioration mechanism of pre-disintegrated carbonaceous mudstone in wetting and drying cycles

为明确干湿循环对预崩解炭质泥岩强度特性和微观结构的影响,通过三轴剪切、扫描电镜试验,分析其强度特性和微观结构参数随干湿循环次数的变化规律,并结合强度指标和微观结构参数之间的联系,揭示预崩解炭质泥岩强度劣化机制。研究结果表明:6次干湿循环后,预崩解炭质泥岩黏聚力和内摩擦角降幅分别达60.10%和8.83%;随干湿循环次数增加,圆形小孔的数量始终最高且呈增大趋势,平均面积最大为0.010μm^(2),同时,部分发育汇集成细长形大孔,平均面积最小为0.626μm^(2);颗粒定向频率Fi(α)整体经历均匀分布、大区间局部优先分布、小区间局部优先分布3个阶段;颗粒定向概率熵、三轴几何平均径降幅分别为4.95%、24.27%;黏聚力主要受小孔、大孔面积影响;内摩擦角主要受颗粒的定向概率熵、三轴几何平均径影响;在干湿循环下,叠聚体反复胀缩,内部应力更加集中,孔隙不断发育,导致黏聚力显著降低;内摩擦角因颗粒定向化及破碎而降低;黏聚力和内摩擦角不同程度的衰减引起预崩解炭质泥岩强度降低。

To clear the influence of wetting and drying cycles on the strength characteristics and microstructure of pre-disintegrated carbonaceous mudstone(PCM),triaxial shear and scanning electron microscopy tests were conducted to analyze the strength characteristics and microstructure parameters of PCM with the increase of the number of wetting and drying cycles,and the strength deterioration mechanism of PCM was revealed by combining the relationship between the strength index and microstructure parameters.The results show that the cohesion and internal friction angle of PCM decrease by 60.10%and 8.83%,respectively,after 6 cycles of wetting and drying.The number of circular pores is always the highest and increases with the maximum average area of 0.010μm^(2).At the same time,some of the pores develop into elongated macropores,with the maximum average area of 0.626μm^(2).The directional frequency of particles generally undergoes three stages:uniform distribution,local priority distribution in large intervals,and local priority distribution between small areas.The decreases of orientation probability entropy and triaxial geometric mean diameter are 4.95%,24.27%,respectively.The cohesion is mainly affected by pore and large pore area.The angle of internal friction is mainly affected by the directional probability entropy and triaxial mean diameter of particles.In the wetting and drying cycle,the polymer expands and contracts repeatedly,the internal stress becomes more concentrated,and the pores develop continuously,leading to a significant decrease in cohesion.The angle of internal friction decreases due to particle orientation and fragmentation.Different degrees of attenuation of cohesion and internal friction angle lead to deterioration of PCM strength.