化学溶液和干湿循环作用下砂岩抗剪强度劣化试验及化学热力学分析

 为研究化学溶液和干湿循环共同作用下砂岩抗剪强度的劣化机制，在不同pH环境下，通过不同干湿循环次数后的单轴、三轴试验，计算出砂岩的黏聚力和内摩擦角，同时得到其与循环次数的关系式，进而获得砂岩在浸泡环境下抗剪强度随干湿循环次数的变化公式。根据砂岩的组成矿物及其百分含量，得到各种主要组成矿物在中性、碱性、酸性溶液中溶解的化学反应方程式，利用化学热力学的基本原理，确定各主要矿物在中性、碱性、酸性溶液浸泡下能否稳定。为了验证分析的正确性，对浸泡溶液中的部分离子(Ca2+，SiO2，Na+，K+)浓度进行测试。结果表明，酸性环境下，砂岩抗剪强度劣化最为严重，碱性次之，中性最轻。在酸性环境中，对抗剪强度影响较大的胶结物主要组成成分(长石、方解石)的性质不稳定，溶解反应能自发进行，而碱性环境中，对强度影响较小的骨料主要组成成分(石英)的性质不稳定，溶解反应能自发进行。酸性浸泡液中，方解石、钾长石、钠长石溶解出的Ca2+，K+，Na+的浓度明显高于中性和碱性液中Ca2+，Na+，K+的浓度，而碱性溶液中，石英溶解出的SiO2的浓度明显高于中性和酸性液中SiO2的浓度，与热力学分析结果一致。

Tests on shear strength deterioration of sandstone under the action of chemical solution and drying-wetting cycles and analysis of chemical thermodynamics

In order to study the deterioration of shear strength of sandstones，specimens were tested through UCS and TCS after different wetting and drying cycles in the environment of different pH values. The cohesion and internal friction angle were calculated，and the relation among the cohesion，internal friction angle and number of cycles was determined and the relationship between the shear strength and the number of cycles in acid and alkali environment was obtained. According to the mineral compositions of sandstone and their contents，the chemical reaction equations of the main mineral in neutral，alkaline，acidic solutions were obtained. The stability of the minerals in the neutral，alkaline and acidic solution was therefore interpreted based on the basic principle of chemical thermodynamics. In order to verify the correctness of the analysis，the concentrations of some ions(Ca2+，SiO2，Na+，K+) in the soaking solution were measured. The results show that the deterioration of the shear strength sandstones is most serious in the acidic environment，secondly in the alkaline environment，and least in the neutral condition. The main compositions of cement，calcite and feldspar，which have a great influence on the shear strength，are unstable in the acid environment because the dissolution reaction occurred spontaneously. The quartz，the main composition of aggregate having little influence on shear strength，is unstable in the alkaline environment with the dissolution reaction occurred spontaneously. The measured concentration of Ca2+，Na+，K+，dissolved from calcite，sodium feldspar，potassium feldspar in acid solution，were significantly higher than that in the neutral and alkaline solution，while the measured concentration of SiO2，dissolved from quartz in the alkaline solution，was significantly higher than that in the neutral and acid solution，which are consistent with the result from the thermodynamic analysis.