水-岩作用下砂岩力学特性及微细观结构损伤演化

Mechanical properties of sandstone and damage evolution of microstructure under water-rock interaction

在库水位反复升降作用下,库岸边坡消落带部分岩体处于浸泡―风干循环状态,其力学特性的劣化将直接影响库岸边坡的变形稳定。以三峡库区库岸边坡消落带砂岩为研究对象,设计并进行了考虑浸泡―风干循环和水压力升降变化的水-岩作用试验。结合SEM电镜扫描,分析了水-岩作用对砂岩微细观结构的影响,采用PFC^2D离散元软件对水-岩作用下砂岩的劣化过程进行了模拟分析。研究结果发现:(1)水-岩作用下砂岩的力学性能劣化效应明显,弹性模量和单轴抗压强度总体呈现先陡后缓的劣化趋势,其中前6次的浸泡―风干循环作用导致的劣化效应尤为明显。(2)水-岩作用下砂岩的微细观结构变化特征明显,由较致密的孔隙式胶结结构逐渐向不规则的蜂窝状结构发展,宏观上就导致了砂岩变形和强度特性的劣化。(3)由PFC^2D离散元模拟分析发现:水-岩作用导致岩石内部颗粒强度和颗粒间黏结强度逐渐劣化,非均匀性增强,荷载作用下的应变局部化特征逐渐明显,整体承载能力逐渐降低,破坏模式由典型的张拉破坏逐渐转变为剪切破坏。

Under the effect of repeated lifting and lowering of the reservoir water level, the rock mass in the dissipated zone is in the soaking-air drying circulation state, which deteriorates its mechanical properties significantly. Thus, the deformation and stability of the bank slope are directly affected. Considering the soaking-air drying cycle and water pressure changes, the water-rock interaction tests were carried out on the sandstone of the bank slope in the Three Gorges Reservoir area. Scanning electron microscope(SEM) was used to analyse the effect of water-rock interaction on the sandstone microstructure. The degradation process of sandstone under the action of the water-rock was simulated using PFC^2D discrete element software. The results showed that the degradation effect of water-rock on sandstone mechanics was significant. It was found that the elastic modulus and uniaxial compressive strength generally showed a steep and slow deterioration trend, and the deterioration effect was particularly obvious in the first six times of immersion-air drying cycle. Under the action of water-rock, the microstructure of sandstone gradually changed from a dense pore-type cementation structure to the irregular cellular structure, which caused the deformation of sandstone and the degradation of strength characteristics macroscopically. Through the analysis of PFC^2D discrete element simulation, it was found that under the action of water-rock, the strength of internal particles and the bond strength between the particles of rock decreased gradually, the heterogeneity of rock increased, strain localisation features under load increased progressively, and the overall bearing capacity reduced slowly. Moreover, the failure mode gradually transformed from the typical tension damage into a shear failure.