大埋深隧洞泥质粉砂岩的三轴蠕变试验与理论分析

Triaxial creep test and theoretical analysis of argillaceous siltstone of large buried deep tunnel

为揭示滇中引水工程香炉山隧洞围岩的非线性蠕变力学特性,对大埋深香炉山隧洞深度1 km处T_(3)sn泥质粉砂岩开展室内三轴蠕变试验,根据试验结果分析不同应力水平下岩样轴向应变随时间的变化规律。通过对试验曲线进行模型辨识,引入开关元件,并与Burgers模型结合形成修正的Burgers模型,将修正的Burgers模型与新提出的非线性黏塑性体串联最终形成非线性黏弹塑性蠕变模型(NVEPB蠕变模型)。通过对NVEPB蠕变模型的本构方程进行Laplace变换,推导NVEPB蠕变模型的一维蠕变方程。通过引入塑性力学知识并结合假设条件,获得NVEPB蠕变模型的三维蠕变方程和常规三轴应力状态下的蠕变方程。借助Origin平台,将NVEPB蠕变模型在常规三轴应力状态下的蠕变方程编程并嵌入其内置的非线性拟合模块,实现蠕变方程的二次开发。通过Origin平台的Levenberg-Marquardt非线性最小二乘法反演获得模型的蠕变力学参数,并将反演拟合计算结果与蠕变试验结果进行对比分析。研究结果表明:NVEPB蠕变模型的拟合曲线和蠕变试验结果高度吻合,拟合系数均在0.94以上,较好地揭示了滇中引水大埋深隧洞围岩的非线性蠕变力学特性。

In order to reveal the nonlinear creep mechanical properties of the surrounding rock mass of Xianglushan tunnel project in central Yunnan province,an indoor triaxial creep test was carried out on the T_(3)sn argillaceous siltstone at Xianglushan tunnel 1 km deep.Combined with the experimental results,the variation of axial strain with time at different stress levels was obtained.Through model identification of the test curve,a switching element was introduced and combined with the Burgers model to form the modified Burgers model.Further,the modified Burgers model and a newly proposed nonlinear viscoplastic body were connected in series to form the NVEPB creep model.The one-dimensional creep equation of the NVEPB creep model was derived by Laplace transform of the constitutive equation of the NVEPB creep model.By introducing the knowledge of plastic mechanics and combining with appropriate assumptions,the creep equations of the NVEPB creep model and the creep equations of the conventional triaxial stress state were obtained.With the help of Origin platform,the creep equation programming of NVEPB creep model in conventional triaxial stress state was embedded into its built-in nonlinear fitting module,which realized the secondary development of creep equation.The creep mechanical parameters of the model were obtained by Levenberg-Marquardt nonlinear least square inversion of Origin platform,and the results of inversion fitting were compared with those of creep test.The results show that the fitting curve of the NVEPB creep model is highly consistent with the creep test results,and the fitting coefficient is above 0.94,which reveals the nonlinear creep mechanical properties of the surrounding rocks of the tunnels with large depth of water diversion in central Yunnan.