单轴条件下砂岩三维破裂过程的CT观测

岩石破裂过程研究一直是岩石力学专家关注的重要问题。本文采用特制的三轴压力仪与医用西门子SOMATOM -plusCT扫描仪结合 ,对砂岩进行了室内单轴压缩试验。通过对砂岩的CT图像和密度损伤增量与应力关系曲线分析 ,结果显示 ,砂岩的破裂演化过程可分为初始损伤的压密、裂纹出现扩展、裂纹归并分岔、裂纹重分岔扩展以及裂纹惯通宏观破坏等五个阶段。在初始损伤的压密阶段 ,砂岩的密度损伤增量为正值 ,速率也为正 ;在裂纹出现扩展阶段 ,砂岩出现局部密度损伤增量减小 ,并随应力增加而由正值转为负值 ,速率也由正变负 ;在裂纹归并分岔阶段 ,砂岩的密度损伤增量全为负值 ,速率也变快 ;在裂纹重分岔扩展阶段 ,砂岩的密度损伤增量继续变负 ,但速率变慢 ;在裂纹惯通宏观破坏阶段 ,砂岩的密度损伤增量继续变负 ,速率变的更快。

X-RAY CT OBSERVATION ON THREE-DIMENSIONAL FRACTURING PROCESS OF SANDSTONE SPECIMEN UNDER UNIAXIAL CONDITION

Fracturing process of rock caused by loading is an important problem in study of failure mechanism of rock. In order to analyze quantitatively the fracturing process of rock, sandstone specimen was tested under uniaxial and triaxial compressions and observed by X-ray . From the result the formula of rock damage variable and its increment and the calculation of rock initial damage variable are proposed. Analyzed CT images and relational curves between stress and density damage increment of sandstone, we found that the fracturing process of sandstone occurred in five stages,i.e. the compaction by initial damage, crack extension, the crack merging and forking of crack, the continuos forking and extension of crack, and the connection of cracks and failure of rock. In the stage of compaction by initial damage, density damage increment of sandstone is positive and the rate ia positive. In the stage of crack extension, local density damage increment of sandstone decreased and changed from positive to negative, and the rates changed also from positive to negative with increasing stress. In the stage of merging and forking of crack, density damage increment of sandstone is negative and the rate became higher. In the stage of continuous forking and extension of crack, density damage increment of sandstone is continuously negative, but the rate became slower. In the stage of connection of cracks and failure of rock, the density damage increment of sandstone is continuously negative and the rate became higher.