砂岩蠕变特性试验及三维非线性力学模型研究

Study on creep characteristics of sandstone and three-dimensional nonlinear mechanical model

为了描述岩石的蠕变力学行为,开展不同围压条件下的砂岩三轴压缩蠕变试验。研究表明:岩石稳定蠕变阶段是岩石微裂纹不断发育和扩展的过程,稳态蠕变速率与围压呈幂函数增长关系;砂岩在围压5 MPa、10 MPa和15 MPa下的长期强度分别为19.8 MPa、22.3 MPa和24.7 MPa,长期强度随围压的增强而递增。基于岩石蠕变的非线性特征,定义了一个与围压相关的黏弹性模量E(p),经过推导变换得到了可反映岩石蠕变受时间和围压影响的E(p,t),应用于改进后的Burgers模型,从而得到新的一维蠕变本构模型。将其拓展到三维应力状态,得到新的三维非线性力学模型,识别蠕变试验数据,对比分析预测效果,证明所建模型的可行性和合理性。研究成果为岩石三维应力状态下蠕变行为模拟提供一定参考。

To describe the creep mechanical behavior of rocks,triaxial compression creep tests of sandstone under different confining pressures are conducted herein.Results show that the steady creep stage is a process of developing and expanding microcracks in rocks,and the steady creep rate and confining pressure increase the power function.The long-term strengths of sandstone under confining pressures of 5 MPa,10 MPa,and 15 MPa are 19.8 MPa,22.3 MPa,and 24.7 MPa,respectively.The long-term strength increases with the increase in confining pressure.Based on the nonlinear characteristics of rock creep,the viscoelastic modulus E(p)associated with confining pressure is defined.E(p,t)that can reflect the influence of rock creep by time and confining pressure is obtained using the derivation transformation,which is applied to the improved Burgers model to obtain a new one-dimensional creep constitutive model.It can be extended to three-dimensional stress state to obtain a new three-dimensional nonlinear mechanical model,identify creep test data,compare and analyze the prediction results,and prove the feasibility and rationality of the model.The research results shed light on the simulation of creep behavior of rock under three-dimensional stress state.