水-岩作用对砂岩卸荷力学特性及微观结构的影响

库岸坡岩体在工程建设中不可避免要遭遇开挖卸荷作用的影响，以三峡库区典型岸坡的层状砂岩为试验对象，设计开展了模拟库水位升降变化和浸泡-风干循环的水-岩作用试验，重点分析了水-岩作用对砂岩卸荷力学特性和微观结构的影响。研究表明：在10次水-岩作用过程中，砂岩的三轴卸荷强度、抗剪强度总体呈先陡后缓的劣化趋势，前4次水-岩作用的劣化速度较快，占总劣化度的70%左右，而后，劣化趋势逐渐趋缓；随着水-岩作用次数的增加，同一围压下岩样卸荷前的变形模量逐渐降低，围压卸载过程中变形模量的线性缓变阶段逐渐变短，非线性突变阶段逐渐变长、变缓，岩样的脆性特征逐渐减弱，塑性逐渐增强；水压力的反复升降变化和浸泡-风干循环作用对岩样造成了不可逆的渐进累积损伤，微观上岩样微裂纹、裂隙、孔隙逐步发育、汇集，宏观上就表现为孔隙率增加、三轴卸荷强度、抗剪强度的劣化。相关研究结论可为库岸边坡岩体开挖卸荷变形稳定分析提供参考。

Effect of water-rock interaction on unloading mechanical properties and microstructure of sandstone

The bank slope of the reservoir is inevitably affected by the excavation unloading during the project construction. In this study, we selected sandstone from the typical bank slope in Three Gorges Reservoir Region. Water-rock cycle experiments were carried out to simulate the variation of water levels and immersion-air drying cycles. Especially, the water-rock interaction effect on unloading mechanical properties and microstructure of stratification sandstone was mainly analyzed. The results showed that in the course of ten times of water-rock cycles, the triaxial unloading and shear strength of sandstone presented initially a steep deterioration and later gradual deterioration trend. The first four times accounted for about 70% in the overall deteriorating degree, which indicated the degree in the last three cycles slowed down. As the water-rock cycle times increased, the deformation modulus of rock specimen decreased gradually before uploading at the same confining pressure. During the unloading process of confining pressure, the linear graded phase of deformation modulus gradually became shorter, whereas the nonlinear mutation phase became longer and slower. The brittle feature of rock specimen slowly weakened, whereas its plasticity enhanced. The repeated fluctuations in water pressure and the immersion-air drying cycle resulted in an irreversible slow and accumulated damage to the rock specimen. Microscopically, micro-cracks, cracks and pores of rock steadily developed and accumulated. Macroscopically, the porosity rate increased, and the triaxial unloading and shear strength decreased. This study can provide references for the analysis of excavation, unloading and deformation of slope rock mass in bank slopes.