酸性条件下砂岩剪切破坏特性试验研究

运用自主研发的煤岩细观剪切试验装置，选取三峡库区三叠系上统的须家河组细砂岩开展室内不同pH值溶液浸蚀后的剪切试验，并借助图像处理技术对砂岩试件在剪切载荷作用下裂纹的时间演化规律进行试验研究，探讨裂纹开裂与砂岩浸蚀程度之间的关系。研究结果表明：岩石在不同时间点剪应力与裂纹演化有明显的相关性，表面裂纹的萌生到失稳断裂是在相对较短的时间内完成的，砂岩的破裂几乎是产生于矿物颗粒边界与胶结物中的绕晶破裂，仅在极少数应力高度集中区域的颗粒上才会出现穿过颗粒的破裂；随着化学溶液酸性的增强和浸蚀时间的延长，砂岩浸蚀程度增大，抗剪强度降低，砂岩剪切破坏时的裂纹开裂宽度相应增大，裂纹开裂情况愈加复杂；化学溶液是引起岩石强度和变形衰减的一个重要原因。

EXPERIMENTAL STUDY OF SHEARING FAILURE PROPERTIES OF SANDSTONE UNDER ACIDIC CONDITIONS

The fine sandstone from the Xujiahe group of Three Gorges reservoir area is selected as object. The effect of various acid solutions with different pH values on sandstone under shearing load is investigated by using the independent development of meso-shear test equipment for coal rock. Simultaneously，temporal and spatial evolution law of microcrack of sandstone sample under the shear loading is researched by image processing technology. The relationship between the crack initiation and the degree of sandstone erosion was investigated. The results show that there is obvious correlation between the shear stress and crack evolution of sandstone at different time points，and process from surface crack?s initiation to the unstable failure of the samples was completed in a relatively short time. In the process of rupture failure of sandstone，it almost produced intergranular fracture in the mineral grain boundaries and cements，and transgranular fracture only produced in highly concentrated region of stress. Furthermore，as the increase of acidic strength of solution and time of erosion，the erosion degree and the deformation of sandstone increased，while the shear strength reduced and the width of crack corresponding increased，crack situation was more complex. Therefore，chemical solution is an important factor which affects the rock?s strength and deformation attenuation.