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为了研究砂岩的力学特性,对砂岩试件开展了不同围压下的常规三轴压缩试验。试验结果显示,随围压增加,砂岩峰值应力、峰值点应变及残余强度均逐渐增大;当围压低于15 MPa时,砂岩弹性模量随围压增加也逐渐增大,但增大幅度逐渐降低;当围压在15 MPa以上时,其弹性模量则与围压无关。为了描述砂岩破坏过程的应力–应变响应,提出一种改进的Duncan-Chang模型,并根据岩石应力–应变曲线峰值点处斜率为0的特点给出模型参数的确定方法。利用砂岩三轴压缩试验结果对模型合理性进行验证。预测曲线和试验结果对比显示,该模型能够准确描述砂岩应变软化特性和不同围压下砂岩破坏过程中除初始压密阶段以外的其余4个阶段,特别是能够反映砂岩破坏后的残余强度。对模型特性的进一步分析表明,除应变软化特性外,该模型还可模拟岩石在高围压下的应变硬化行为,具有较强的适应性。
In order to study the mechanical properties of sandstone, conventional triaxial compression tests under different confining pressures were carried out on sandstone specimens. The results show that with the increase of confining pressure, the peak stress, the peak point strain and the residual strength of sandstone increase gradually. When the confining pressure is lower than 15 MPa, the elastic modulus of sandstone increases with the increase of confining pressure, but increases gradually When the confining pressure is above 15 MPa, the elastic modulus is independent of confining pressure. In order to describe the stress-strain response of sandstone failure process, an improved Duncan-Chang model is proposed and the method to determine the model parameters is given according to the slope of 0 at the peak point of the stress-strain curve of rock. The sandstone triaxial compression test results were used to verify the rationality of the model. The comparison between the predicted curve and the experimental results shows that the model can accurately describe the strain softening characteristics of sandstone and the remaining four phases in the process of sandstone destruction under different confining pressure except the initial compaction stage, especially the residual strength after sandstone failure. Further analysis of the characteristics of the model shows that in addition to the strain softening characteristics, the model can also simulate the rock strain hardening behavior under high confining pressure, and has strong adaptability.