弯曲加卸载下杂质盐岩断裂力学行为特征研究

为研究弯曲荷载下杂质盐岩断裂力学行为及损伤演化规律,利用四川大学MTS815岩石力学测试设备及三维声发射监测系统,展开了纯盐岩、含杂卤石盐岩及杂质盐岩三点弯曲加卸载试验。试验结果表明：(1)杂卤石及泥质胶结提升了盐岩的韧性,纯盐岩的断裂韧度均值KIC=6.36MPa.mm^-0.5,杂卤石盐岩的断裂韧度较纯盐岩高43.08%,杂质盐岩的断裂韧度为纯盐岩的3.18倍；(2)杂质导致盐岩脆性提高,纯盐岩声发射事件覆盖区域大于杂卤石盐岩及杂质盐岩；三点弯曲加卸载下岩石内部声发射事件由切槽尖端逐渐向荷载点扩散,直至岩石完全断裂；(3)盐岩损伤程度随循环次数增长逐渐提高,但增长速度逐渐降低,损伤变量与切槽张开度符合指数函数关系,损伤变量-张开度曲线拐点对于研究岩石失稳倾向性具有一定的预测效果；(4)声发射参数rc值能够反映盐岩弯曲加卸载破坏全过程中主裂纹与微裂纹的发展趋势,峰后残余阶段纯盐岩及杂卤石盐岩rc曲线持续上升,微裂隙稳定发展；杂质盐岩表现出更强的脆性,其在峰后残余阶段rc曲线表现出与纯盐岩及杂卤石盐岩相反的变化趋势。

Investigation on Fracture Mechanical Behavior of Salt Rock With Impurities Under Bending Loading-unloading Conditions

In order to investigate the fracture mechanical behavior and damage evolution law of salt rock with impurities under bending, three-point bending loading and unloading tests of pure salt rock, halogen bearing salt rock and salt rock with impurities were carried out by using MTS815 rock mechanics testing equipment and three-dimensional acoustic emission monitoring system of Sichuan university. The results show that :(1) the toughness of salt rocks is enhanced by the bonding of heterogenite and shale. The mean fracture toughness of pure salt rocks under three-point bending and unloading is KIC= 6.36MPa .mm^-0.5. The fracture toughness of heterogenite salt rocks is 43.08% higher than that of pure salt rocks, and the fracture toughness of impurity salt rocks is 3.18 times higher than that of pure salt rocks. (2) impurities lead to the improvement of brittleness of salt rock,the area covered by the acoustic emission events of pure salt rock is larger than that of heterogenite salt rock and rock salt with impurities.Under three-point bending loading and unloading, acoustic emission events in the rock gradually spread from the groove tip to the load point until the rock is completely fractured. (3) the degree of salt rock damage increases gradually with the increase of cycle times, but the growth rate decreases gradually.and the relationship between damage variable and groove opening conforms to the exponential function. The inflection point of the curve of damage variable-opening degree has certain prediction effect on the study of rock instability tendency. (4) the rc value of AE parameter can reflect the development trend of main cracks and microcracks in the whole process of salt rock bending, loading and unloading failure. In the residual stage after peak, the rc curve of pure salt rock and heterogenitesalt rock continues to rise, and the microcracks develop steadily. The impurity salt rocks show stronger brittleness, and the rc curve of the residual post-peak stage shows the opposite change trend to that of the pure salt rocks and the hetero halite salt rocks.