开挖损伤区近场模型THM耦合过程的BMT模拟

BMT SIMULATION OF COUPLED THM PROCESSES BY NEAR FIELD MODEL IN EXCAVATION DAMAGE ZONE

以正在进行的大型国际合作项目DECOVALEX-THMC为背景,利用自行开发的弹塑性细胞自动机模拟系统,对开挖损伤区近场模型域进行程序校验(BMT)模拟研究,揭示高放废物从处置开始直至1×106a的演化过程中,裂隙的存在对开挖损伤区力学性能的影响。首先进行的是弹性分析,研究对象包括开挖损伤区近场均质模型和包含复杂裂隙网络的非均质模型域,该裂隙网络是瑞典?sp?硬岩实验室根据裂隙映射得出的真实裂隙网络分布。引入简单的弱化参数表达式,用弱化元胞单元来代表模型中的复杂裂隙网络,以模拟裂隙的软化效应。采用项目指导委员会提供的随时间变化的温度、应力、水流边界条件,模拟地质围岩从开挖、核废物处置、加热100～1×106a的力学演化过程。模拟结果显示,裂隙的存在对应力场、变形场和破坏过程有较大的影响,并将模拟的结果与国际上其他研究小组的模拟结果进行对比,吻合较好,说明该模型和方法的合理性,并可适合于该项目下一步的研究工作。在此基础上,采用弹塑性细胞自动机模拟系统,对裂隙网络模型和均质模型进行弹塑性破坏过程分析,结果表明,由于裂隙的存在,裂隙网络模型的破坏过程更加复杂。

The results of benchmark test（BMT） from the study on coupled thermo-hydro-mechanical（THM） processes in the excavation damage zone（EDZ） around nuclear waste repository in fractured rocks are presented. This is an important part of international cooperation project DECOVALEX-THMC TASK B. The results focus on the influence of fractures on the evolution of EDZ over 1 × l0^6 years after disposal of high-level radioactive waste. The numerical study is conducted for two model domains, homogeneous and heterogeneous near-field models, surrounding a repository. The heterogeneous near-field model domain includes a realistic fracture network derived by detailed fracture mappings at the Asp6 hard rock laboratory, Sweden. In this study, fractures are represented discretely, but softening and weakening effects of fractures intersecting a continuum element are simulated using continuum elements by a reduction in modulus. Using this approach for fracture representation, numerical analyses are conducted using elastoplastic cellular automata（EPCA） code. Elastic and elastoplastic analyses are performed to study the evolution of stress and deformations in EDZ adopting time-dependent thermal, mechanical and fluid pressure boundary conditions. The analysis shows a strong impact of fractures on the distribution of rock stress and deformation as well as the failure process. The numerical results are consistent with those obtained by other international research teams, indicating the validity of EPCA code. The results also indicate that the EPCA code can be used to perform next step analysis of DECOVALEX-THMC project.