酸性溶液作用下砂岩损伤时效特性机制分析

Mechanism Analysis of Sandstone Damage-Aging Characteristics under Action of Acidic Solution

为探究酸性溶液作用下砂岩损伤时效特征,以高黎贡山隧道岩溶段砂岩为试验研究对象,借助扫描电镜和XRD衍射试验分析酸性溶液对砂岩宏观形貌、缺陷形态、孔隙结构、矿物组成成分以及孔隙率的改造作用,在不同浸泡时间节点对不同溶液中砂岩试件的质量、尺寸及三轴抗压强度等进行测量。试验结果表明:1)溶液pH越低,同一时间节点内试件的孔隙率、质量和尺寸相对变化越大,且在各溶液中初期变化速率达到最快,后期均呈平稳趋势;2)在围压20 MPa条件下,与pH=7的溶液中49 d的岩样相比,pH=1的溶液中试件的三轴峰值抗压强度累计降低20.98%,其下降速率随时间推移而减缓,黏聚力与内摩擦角均随时间增加呈下降趋势,且黏聚力对酸性溶液的敏感程度高于内摩擦角;3)在酸性溶液侵蚀作用下,试件内长石与方解石等组成成分大量消耗致使试件微观结构改变,且随着溶液pH值降低,试样孔隙间距增大,胶结物消耗加剧,溶蚀孔洞及微裂隙发育较好。

To investigate the damage-aging characteristics of sandstone under the action of acidic solution, experiments are conducted on the sandstone in the karst section of the Gaoligongshan tunnel. The transformation effects of acidic solution on the macroscopic morphology, defect morphology, pore structure, mineral composition, and porosity of sandstone are analyzed via scanning electron microscopy and X-ray diffraction experiments. The mass, size, and triaxial compressive strength of sandstone specimens in different solutions are measured at different immersion time nodes. The test results indicate the following:(1) The lower the solution pH, the greater the relative changes in porosity, mass, and size of the specimen;the change rate is rapid in the initial stage of each solution and exhibits a stable trend in the later stage.(2) Under a confining pressure of 20 MPa, compared with the rock sample in the solution of pH=7 for 49 days,the triaxial peak compressive strength of the specimen in the solution of pH=1 is reduced by 20.98%, and the decrease rate declines with time. The cohesion and internal friction angle decrease with time, and the sensitivity of cohesion to the acidic solution is higher than that of the internal friction angle.(3) Under the erosion of acidic solution, the large consumption of feldspar and calcite and other components in the specimen changes the microstructure of the specimen.With a decrease in the pH of the solution, the specimen pore spacing increases, the cement consumption increases, and the corrosion holes and microcracks develop well.