基于颗粒流程序的非定常西原体模型

为实现岩石试样蠕变全过程的准确模拟,并从细观角度探究蠕变过程中微裂隙的发生和发展规律,在二维颗粒流程序(PFC2D)中开发出具有黏弹塑性特征的西原体流变接触本构模型,进一步提出包含两种非定常元件的非定常西原体模型,推导了模型本构关系和蠕变方程.在PFC2D中调用自定义西原体流变模型,通过参数调试,获得与真实试样具有相同强度特性的数值试样.以室内单轴压缩蠕变试验数据为基础,在Matlab中对模型非定常参数进行拟合反演分析.在此基础上,进行单轴压缩蠕变试验的模拟,计算过程中分别采用定常和非定常两种模型,并对微裂隙进行监测.对比分析结果表明:定常模型仅适用于衰减和稳定蠕变阶段;非定常模型也可用于描述加速蠕变阶段,从而准确模拟蠕变全过程;加速蠕变阶段主要是由微裂隙的加速发展而产生,加速蠕变将导致试样剪切破坏. 

Non-stationary Nishihara model in the particle flow code

In order to accurately simulate the whole process of rock creep and explore the generation and development of mircofractures from the meso-level,a visco-elastoplastic Nishihara rheological constitutive model is developed in the two-dimensional particle flow code(PFC2D). Then a non-stationary Nishihara model including two non-stationary elements is put forward in this article. A constitutive equation and a creep equation are derived based on the non-stationary Nishihara model. The user-defined Nishihara constitutive model is called in PFC2D,and a numerical sample whose strength properties are the same as those of a real rock specimen is acquired by parameter testing. Using the data of uniaxial creep tests in laboratory,the non-stationary parameters are back analyzed in Matlab. At last,uniaxial creep tests are simulated using the stationary and non-stationary models,and micro-fractures are monitored.A comparison of these results show that the stationary model can only be used to describe the decay and steady stages,while the nonstationary model is also applicable to the accelerated stage,and thus can simulate the whole process of rock creep. Accelerated creep results from the accelerated development of mirco-fractures and leads to shear failure.