压剪应力条件下砂岩双面剪切细观开裂扩展演化特性试验研究

 利用自主研发的煤岩双面剪切细观开裂演化过程试验装置，通过开展不同法向应力条件下的剪切试验，借助声发射技术及图像处理技术，对细观开裂扩展过程、细观开裂扩展空间分布进行深入探究。研究结果表明：对于压剪应力条件下的双面剪切试验，加载过程中的大部分阶段，试件表面损伤不明显，表面裂纹出现在峰值剪应力之前；当剪应力达到峰值前，Hit率有一个急剧增加的过程，说明砂岩内部已有裂纹产生，而试件表面并无明显变化，一段时间后才在表面观测到细小裂纹，推测裂纹由内向外扩展；试件发生宏观破坏后，左右两侧裂纹呈八字形或梯形分布，由于竖向剪切力引起的岩体内部剪切破坏占主导作用且砂岩内部晶粒间存在一定的几何物理性质差异，主裂纹基本沿预定剪切面扩展的同时表现出开裂扩展的不规则性；裂纹多在石英、长石等矿物颗粒的边缘即砂岩中相对薄弱的环节产生，随着应力水平的增加，裂纹也会穿过矿物颗粒形成穿晶破裂，这种现象多在石英颗粒中出现，这与其特有的微结构特征有关。

MESOSCOPIC CRACKING AND EXPANSION OF DOUBLE SHEARED SANDSTONE UNDER COMPRESSIVE-SHEAR STRESS

The mesoscopic test device developed studying the crack process of coal and rock under double shear was used in the shear test at different stress conditions. The acoustic emission and image processing techniques were employed to measure the mesoscopic cracking propagation process and the mesoscopic cracking extension space distribution. For the double shear test under compression and shearing，the damage of the surface of the specimen is not visible in most of the period of loading process and the surface cracks occur just before the shear stresses reach the peak value. When the shear stresses are nearly reaching the peak，the rate of Hit has a sharp increase indicating that there are already cracks inside the sandstone，while on the surface there are no cracks，and the tiny cracks can only be seen after a period of time. Presumably，the cracks developed from inside to outside. After the macroscopic damage，the left and right sides of cracks show a splayed or trapezoidal distribution. Because the internal shear failure of rock mass is mainly caused by the vertical shear force and the sand grains possess the different geometric and physical properties，the main crack along the shear plane extended irregularly. Cracks always occur in the edges of mineral particles like quartz，feldspar etc which are the weakest links of sandstone. As the shear stress level increases，the cracks will cross over the mineral particles and form transgranular fractures. This phenomenon is often seen in quartz grains because of its specific relevant microstructure features.