酸性干湿循环作用下砂岩强度参数劣化规律

为研究酸性环境中砂岩在干湿循环作用下强度的劣化规律，在溶液pH值分别为7、5、3的浸泡环境中，对砂岩试样进行循环次数为1、5、10、15、20次的干湿循环试验。根据每个循环阶段后的强度数据，得到Mohr-Coulomb强度准则参数和Hoek-Brown强度准则参数，并对这些参数的干湿循环劣化效应做简要的分析。再根据应力空间中偏应力与强度准则参数的关系式，分别作出pH值为7、5、3的浸泡溶液作用下π平面上的破坏面随不同循环次数的变化图。结果表明：各准则参数随着干湿循环次数的增加呈下降趋势，循环次数较小时劣化较为严重，而后呈缓和趋势；pH值越低，劣化越严重，劣化效应由大至小依次为：单轴抗压强度、黏聚力、材料常数、内摩擦角；同一pH值浸泡环境中，循环次数较小时，π平面上的破坏曲线较为稀疏，循环次数越大，破坏曲线越密集；不同pH值浸泡环境中，pH越低，破坏曲面越小；偏应力与单轴抗压强度、黏聚力正相关，与材料常数、内摩擦角负相关。

Deterioration rules of strength parameters of sandstone under cyclical wetting and drying in acid-based environment

To investigate the deterioration rule and failure criterion of rock in the acid-based environment, experiments were conducted on sandstone specimens after 1, 5, 10, 15, and 20 times of wetting and drying cycles in the environment of pH=7, 5 and 3, respectively. By analysing uniaxial compressive strength (UCS) and triaxial compressive strength (TCS) after different cycles, the parameters of Mohr-Coulomb failure criterion and Hoek-Brown failure criterion were calculated, and the effect of wetting and drying cycles on these parameters is also analysed. Finally, according to the relationship formula between the deviatoric stress and the strength criterion parameters in the stress space, the failure envelopes changed with cycles in the π-plane were drawn under the action of solutions with pH values of 7, 5, and 3. The results show that the parameters of strength criterion decrease with the increase of cycle time, at the early stage of cycles, the deterioration is more significant, and then the deterioration is relatively low. The lower the pH value is, the more serious the deterioration is, and the degrees of deterioration effect from large to small are as follow UCS, cohesion, material constant and internal friction angle. In the same environment of pH value, when the cycle number is low, the failure envelopes in the π-plane are relatively sparse. However, the greater the number of cycles are, the denser the failure envelope is; in the different immersion environment of pH value is, the lower the pH value is, the smaller the failure plane is. The deviatoric stress is positively correlated with UCS and cohesion, but negatively correlated with the material constant and internal friction angle.