砂岩力学特性及其改进Duncan-Chang模型

 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。

Mechanical properties of sandstone and an improved Duncan-Chang constitutive model

In order to study the mechanical properties of sandstone，the conventional triaxial compression tests under different confining pressures were carried out on sandstone specimens. The test results indicate that the peak stress，the strain at peak point and the residual strength of sandstone increase gradually with the increase of the confining pressure. When the confining pressure is less than 15 MPa，the elastic modulus of sandstone increases with the increasing of confining pressure，but the rate of variation is smaller and smaller. When the confining pressure is larger than 15 MPa，the elastic modulus is independent of the confining pressure. The Duncan-Chang constitutive model was revised to describe the stress-strain response in the failure process of sandstone. The method of parameter determination was put forward based on the characteristic of the slop is 0 at the peak point of stress-strain curve. The triaxial compression test results of sandstone were used to evaluate the reasonability of the revised Duncan-Chang model. The comparison of predicted curves from the model and the test results shows that this model can accurately describe the strain softening property of sandstone and the other four stages of the failure process of sandstone under different confining pressures except for the closure stage of cracks. Especially，the model reflects the residual strength after sandstone failure. The further analysis on the model characteristics indicates that in addition to the strain softening property，the revised Duncan-Chang model can also simulate the strain hardening behavior of rock under the action of high confining pressure. So，this model has the good adaptability.