渗透环境下化学腐蚀裂隙岩石破坏过程的CT试验研究

CT EXPERIMENTAL RESEARCH OF FRACTURED ROCK FAILURE PROCESS UNDER CHEMICAL CORROSION AND PERMEATION

通过CT扫描试验研究渗透及无渗透环境下受化学腐蚀及未受化学腐蚀预制裂隙砂岩的三轴压缩破坏过程,分析试件破坏过程中各层面的CT数变化规律,并对渗透环境下不同试验阶段试验参数的变化规律以及渗透环境对砂岩强度的影响进行分析。试验结果表明,在微裂隙扩展与主裂隙贯通的过程中,对于无渗透环境,由于微裂隙发育导致裂尖处有所密合,之后随着试件的破裂CT数逐步减小;而对于渗透环境,由于孔隙水压力作用,在此过程中裂尖处无密合现象,而是继续开裂,CT数继续减小直至破坏。试件破坏后,无渗透环境下试件破坏时产生的裂隙较单一,而渗透环境下由于渗透作用和孔隙水压力作用,试件破坏时产生的裂隙相对来说较复杂,说明渗透环境对试件的破坏损伤作用较大。在试件变形从应力–应变曲线的线性阶段开始到裂尖破裂阶段,渗透环境的影响对应力以及变形所经历的时间大小起主要决定作用;在试件变形从裂尖破裂到裂隙贯通阶段,应力以及变形所经历的时间受化学腐蚀程度和渗透环境共同影响。渗透环境对砂岩强度的影响非常明显,无渗透环境下试件的强度远大于渗透环境下试件的强度,如试件经浓度为0.01 mol/L,pH值为2的NaCl溶液腐蚀后,其强度只有无渗透环境下的16.6%。

Real-time computerized tomography（CT） experimental results of sandstone failure process under triaxial compression with chemical corrosion and permeation of chemical solution are presented. The changes of CT numbers of every scanning layer are analyzed under triaxial compression with and without permeation at different CT scanning stages; and the stress and time that deformation lasts in different testing stages are studied for sandstone samples with and without corrosion under triaxial compression with and without permeation. The effect of permeation on sandstone strength is obtained. The test results of CT images and CT numbers show that crack-tip closure is resulted from the development of microcrack under the environment without permeation during the process of microcrack propagation to principal crack coalescence, after which cracking continues under the environment with permeation due to pore water pressure. Because of permeation and pore water pressure, more cracks are generated in the specimens under the environment with permeation but they are relatively single in the specimens under the environment without permeation. From initial linear elastic deformation to crack-tip fracture, the effect of permeation on the stress and time that deformation lasts is main key factor and the chemical corrosion is a secondary factor. From crack-tip fracture to crack coalescence, the stress and time that deformation lasts are decided by both permeation and chemical corrosion. The effect of permeation on sandstone strength is obvious. The strength is much greater under the environment without permeation than that with permeation. For example, the strength under the environment with permeation occupies 16.6% of that without permeation for the specimens corroded by NaCl solution with concentration of 0.01 mol/L and pH value of 2.