干湿交替作用后砂岩破裂过程实时观测与分析

Real-time observation and analysis of fracturing process of sandstone under cyclic drying and wetting

采用岩石破裂全过程的细观力学试验系统进行了天然状态及干湿交替作用后的完整和含预制圆孔砂岩试件的单轴压缩破裂试验。利用显微镜观察了砂岩裂纹萌生、扩展以及试件的失稳破坏过程。经过干湿交替作用后岩样更容易在较低的应力状态下发生裂纹的扩展,并且裂纹扩展的初始阶段一般表现为拉破裂。完整试件的裂纹是随机性的三维扩展,而有预制圆孔试件一般是从预制圆孔周边开始扩展。天然状态下的预制圆孔试件在起裂时从圆孔的压应力集中区产生剪切裂纹;而干湿交替作用后,起裂时可能先从拉应力集中区产生拉裂纹,并且裂纹演化过程更为复杂一些,破裂形式多样化。与天然状态相比,经过干湿循环作用后的砂岩破坏脆性降低,强度等力学参数也随干湿交替次数增加而逐渐降低。

A number of integrated and pre-existing hole sandstone specimens under cyclic drying and wetting have been prepared and tested under compression with meso-mechanical testing system.The processes of crack initiation,propagation and failure behaviors of specimens are observed by microscope.After several cyclic times of drying and wetting,the cracks initiate at lower load level,and the initial cracks generally are tensile cracks.The crack propagation in integrated specimens is three-dimensional at random,but in the specimens with pre-existing hole,the cracks start to grow at the hole wall firstly.In specimens with pre-existing hole,shearing cracks initiate from the compressive stress concentrated areas of the hole wall under natural state;on the contrary,tensile cracks may initiate at the central zone of tensile stress under cyclic drying and wetting.Moreover,the cracking progress is more complicated and its rupture form is multiple.Compared with natural specimens,the specimens under cyclic drying and wetting become more ductile,and their strength parameters are lower.