应变加载速率对盐岩力学性能的影响

EFFECTS OF LOADING STRAIN RATE ON MECHANICAL PERFORMANCES OF SALT ROCK

对盐岩进行不同围压下变应变加载速率的三轴压缩强度与变形特性的室内测试,分析应变加载速率对盐岩三轴强度、轴向应变及侧向应变以及破裂形式等物理力学性质的影响。在所测试的应变加载速率范围内,加载速率对盐岩三轴强度的影响可分为3个阶段:无明显影响的弹性阶段、强度差异形成的塑性阶段初期、强度差异保持的应变硬化阶段,最终的结果是抗压强度随着加载速率的提高而增大。对试验后岩样的破坏形式进行细观分析可知,高应变加载速率对盐岩内部结构造成的破坏更明显,裂纹长度大且外观明显,与低应变率下的裂纹破裂形式有显著的差异。对三轴试验后的岩样进行单轴压缩测试,发现三轴试验时的应变率较大,试验后岩样的弹性模量越小,表明高应变率导致盐岩的结构破坏更严重,对盐岩的内部损伤越大。对比不同围压下的试验数据并结合其他单轴试验下的研究结果,得出围压是加载速率对盐岩性质有无影响的先决条件,并且围压越高加载速率对盐岩力学性质的影响越明显的结论。以本次试验研究所得成果出发,结合实际工程中盐岩溶腔的各种用途以及建造、运营的各个阶段内不同的盐岩应变率进行分析,提出对工程有益的建议。

Through the triaxial compression test of salt rock under different confining pressures and loading strain rates, influences of loading strain rate on salt rock compressive strength, axial strain, radial strain, Young＇s modulus and failure mode are analyzed. In the test scale of loading strain rate, it is found that the influencing characters of salt rock can be divided into three different stages, i.e. elastic stage in which loading strain rate has no effect on salt rock properties, preliminary plastic stage caused by compressive strength difference, and strain hardening stage caused by the stability of strength difference. The final result is that compressive strength increases with the increasing loading strain rate. Test samples under high loading rate have notable internal damage. Cracks appear in these samples are long and obvious which are different from the cracks under low loading rate. The uniaxial compression experiment is undertaken on the rock samples which have been loaded by triaxial compression test. It is found that the Young＇s modulus becomes smaller as the loading rate increases, so high strain rate leads to inattentive internal structure and causes more serious structural damage of salt rock. Comparing test results under different confining pressures and combining with uniaxial compression test results, it is found that confining pressure is the precondition of whether the loading rate has influence on properties of salt rock. The higher the confining pressure is, more obvious the influence of loading strain rate on mechanical performances of salt rock is. From the results of experiment, analysis of different strain loading rates of every stage in construction and operation of salt rock cavern in actual project, several beneficial suggestions are proposed.