双重孔隙介质THMM耦合模型及其有限元分析

建立了一种饱和-非饱和遍有节理岩体的双重孔隙-裂隙介质热-水-应力-迁移耦合模型,其特点是应力场和温度场是单一的,但具有不同的孔隙渗流场、裂隙渗流场和孔隙浓度场、裂隙浓度场,以及可考虑裂隙的组数、间距、方向、连通率和刚度对本构关系的影响;并开发了相应的二维有限元程序.针对一个假定的高放废物地质处置库,就岩体为非饱和双重孔隙-裂隙介质和放射性核素泄漏的情况进行了数值分析,考察了岩体中的温度、负孔隙水压力、饱和度、地下水流速、核素浓度和主应力的状态.结果显示:孔隙和裂隙中的负水压力及核素浓度呈现不同的变化、分布;尽管裂隙水饱和度平均仅为孔隙水饱和度的1/10,但因裂隙的渗透系数比孔隙的渗透系数大4个数量级,故裂隙中地下水的流速约是孔隙中相应值的3倍;孔隙和裂隙中核素浓度的量值接近.

COUPLED THERMO-HYDRO-MECHANICAL-MIGRATORY MODEL AND FEM ANALYSES FOR DUAL-POROSITY MEDIUM

One kind of coupled thermo-hydro-mechanical-migratory model of dual-porosity medium for saturated-unsaturated ubiquitous-joint rockmass was established, in which the stress field and the temperature field are single, but the seepage field and the concentration field are double, and the influences of sets, spaces, angles, continuity ratios, stiffnesses on the constitutive relationship of the dual-porosity medium can be considered, and also the corresponding two-dimensional program of finite element method was developed. Taking a hypothetical nuclear waste repository as a calculation example, the case in which the rockmass is unsaturated dual-porosity medium and radioactive nuclide leak was simulated numerically, and the temperatures, negative pore pressures, saturations, flow velocities, nuclide concentrations and principal stresses in the rockmass were investigated. The results show that: (1) the negative pore pressures and nuclide concentrations in the porosity and fracture systems present different changes and distributions; (2) even though the saturation degree in porosity system is only about 1/10 of that in fracture system, the flow velocity of underground water in fracture system is about 3 times of that in porosity system because the permeability coefficient of fracture system is almost four orders higher than that of porosity system; (3) the value of nuclide concentration in fracture system is close to that in porosity system in the medium.