为研究干湿循环作用下砂岩性能,将南龛石窟砂岩制备成标准的圆柱形试样,结合石窟区域环境条件设计室内干湿循环试验;对比不同循环次数下岩体的劣化模式、质量损失、力学参数和溶液离子变化规律,以及循环前后试样矿物成分、元素含量、胶结特征和颗粒粒径变化特征。研究结果表明：风化前后岩石内长石类矿物水化分解,导致其含量减少,黏土类矿物含量增加;岩石内部Fe、Ca、Mg等主要的胶结元素快速流失,导致颗粒间胶结物流失和岩体微观结构出现损伤断裂,局部出现矿物解体现象;随着循环次数的增加,岩石的抗压强度和抗剪强度逐渐降低,颗粒间的粘聚力C随循环次数呈线性减小趋势,对颗粒间的内摩擦角Φ值影响较小;干湿循环主要导致岩石表面粒径较粗的颗粒流失,同时粘粒含量相对减少,使岩石表面颗粒粒径范围更加集中。

To study the performance of sandstone under dry-wet cycles, standard cylindrical specimens were prepared from the sandstone of Nankan Grottoes, and indoor dry-wet cycle tests were designed based on the environmental conditions of the grotto area, through comparing the degradation patterns, quality losses, mechanical parameters, and changes in solution ions of rock masses under different cycles, as well as the mineral composition, element content, cementation characteristics, and particle size changes of the samples before and after cycling. The research results indicate that the hydration and decomposition of feldspar minerals in rocks before and after weathering lead to a decrease in their content and an increase in the content of clay minerals. The rapid loss of major cementing elements such as Fe, Ca and Mg inside the rock, leads to the loss of cementing fluid between particles and damage and fracture of the microstructure of the rock mass, resulting in local mineral disintegration; As the number of cycles increases, the compressive strength and shear strength of the rock gradually decrease, and the cohesive force C between particles decreases linearly with the number of cycles, with little effect on the internal friction angle Φ between particles. The dry-wet cycle mainly causes the loss of coarser particles on the rock surface, while the content of clay particles is relatively reduced, resulting in a more concentrated range of particle sizes on the rock surface.