The pressure solution model of granular aggregates was introduced into a FEM code which was developed for the analysis of thermo-hydro-mechanical(T-H-M) coupling in porous medium. Aimed at creating a hypothetical model of nuclear waste disposal in unsaturated quartz aggregate rock mass with laboratory scale, two 4-year computation cases were designed: 1) The porosity and permeability of rock mass are functions of the pressure solution; 2) The porosity and the permeability are constants. Calculation results show that the magnitude and distribution of stresses in the rock mass of these two calculation cases are roughly the same. And, the porosity and the permeability decrease to 43%-54% and 4.4%-9.1% of their original values after case 1 being accomplished; but the negative pore water pressures in cases 1 and 2 are respectively 1.0-1.25 and 1.0-1.1 times of their initial values under the action of nuclear waste. Case 1 exhibits the obvious effect of pressure solution.
The models of stress corrosion, pressure solution and flee-face dissolution/precipitation were introduced. Taking a hypothetical nuclear waste repository in an unsaturated dual-porosity rock mass as the calculation objective, four cases were designed 1） the fracture aperture is a function of stress corrosion, pressure solution and free-face dissolution/precipitation; 2） the fracture aperture changes with stress corrosion and pressure solution; 3） the fracture aperture changes with pressure solution and free-face dissolution/precipitation; 4） the fracture aperture is only a function of pressure solution, and the matrix porosity is also a function of stress in these four cases. Then, the corresponding two-dimensional FEM analyses for the coupled thermo-hydro-mechanical processes were carried out. The results show that the effects of stress corrosion are more prominent than those of pressure solution and free-face dissolution/precipitation, and the fracture aperture and relevant permeability caused by the stress corrosion arc only about 1/5 and 1/1000 of the corresponding values created by the pressure solution and free-face dissolution/precipitation, respectively Under the action of temperature field from released heat, the negative pore and fracture pressures in the computation domain rise continuously, and are inversely proportional to the sealing of fracture aperture. The vector fields of flow velocity of fracture water in the cases with and without considering stress corrosion are obviously different. The differences between the magnitudes and distributions of stresses within the rock mass are very small in all cases.
An empirical expression of cohesion （C） and friction angle （Ф） for layered rock was suggested. This expression was compared with a test result made by the former researchers. The constitutive relationship of a transversely isotropic medium and Mohr-Coulomb criterion in which C and Ф vary with directions were employed, and a relative 3D elasto-plastic FEM code was developed, in which the important thing was to adopt a search-trial method to find the orientation angle （p） of shear failure plane （or weakest shear plane） with respect to the major principal stress as well as the corresponding C and Ф Taking an underground opening as the calculation object, the numerical analyses were carried out by using the FEM code for two cases of transversely isotropic rock and isotropic rock, respectively, and the computation results were compared. The results show that when the rock is a transversely isotropic one, the distributions of displacements, plastic zones and stress contours in the surrounding rock will be non-axisymmetric along the tunnel＇s vertical axis, which is very different from that of isotropic rock. The stability of the tunnel in transversely isotropic rock is relatively low.
In order to consider the influence of temperature and underground water movement, an elastoplastic model and a 2D FEM stress fields on the migration of radioactive nuclide with code for analysis of coupled thermo-hydro-mechanical （THM） processes in saturated and unsaturated porous media were extended and improved through introducing the percolation and migration equation, so that the code can be used for solving the temperature field, flow field, stress field and nuclide concentration field simultaneously. The states of temperatures, pore pressures and nuclide concentrations in the near field of a hypothetical nuclear waste repository were investigated. The influence of the half life of the radioactive nuclide on the temporal change of nuclide concentration was analyzed considering the thermo-hydro-mechanical-migratory coupling. The results show that, at the boundary of the vitrified waste, the concentration of radioactive nuclide with a half life of 10 a falls after a period of rising, with the maximum value of 0.182 mol/m3 and the minimum value of 0.181 mol/m^3 at the end of computation. For a half life of 1 000 a, the concentration of radioactive nuclide always increases with the increase of the time during the computation period; and the maximum value is 1.686 mol/m^3 at the end of the computation. Therefore, under the condition of THM coupling, the concentration of radioactive nuclide with a shorter half life will decrease more quickly with water flow; but for the radioactive nuclide with a longer half life, its concentration will keep at a higher level for a longer time in the migration process.
Taking the Kunlunshan Tunnel on Qinghai Tibet Railway as an engineering background, the curved wall-inverted arch lining of the tunnel was simplified into the straight wall-umbrella arch one, and the fractured rock mass with developed joints was treated as a discrete medium in the calculation. Using the UDEC code, the numerical simulations for thermo-mechanical coupling processes in the surrounding rock mass-supporting system were carried out aiming at the conditions of mean temperature, extreme highest temperature and extreme lowest temperature in one year. The distributions and changes of stresses, displacements, plastic zones, temperatures in the rock mass of near field, as well as the loading states in the model-building concrete and bolting were investigated and compared for these three computation cases. The results show that compared with the case of mean temperature, the ranges, where the temperatures of surrounding rock mass change obviously, are 6.0 m and 6.5 m, respectively, for the cases of extreme highest temperature and extreme lowest temperature; the displacements of tunnel are raised by 3.2 9.3 and 5.7 12.7 times, and the thicknesses of plastic zones reach 1.5 2.5 m and 2.0 4.5 m for case 2 and 3, respectively; the extreme temperatures of air have strong effects on the stress, deformation and failure states of supporting structure of tunnel in cold region, and the influence degree of extreme lowest temperature is the highest.
The model of pressure solution for granular aggregate was introduced into the FEM code for analysis of thermo-hydro- mechanical （T-H-M） coupling in porous medium. Aiming at a hypothetical nuclear waste repository in an unsaturated quartz rock mass, two computation conditions were designed： 1） the porosity and the permeability of rock mass are fimctions of pressure solution; 2） the porosity and the permeability are constants. Then the corresponding numerical simulations for a disposal period of 4 a were carried out, and the states of temperatures, porosities and permeabilities, pore pressures, flow velocities and stresses in the rock mass were investigated. The results show that at the end of the calculation in Case 1, pressure solution makes the porosities and the permeabilities decrease to 10%-45% and 0.05%-1.4% of their initial values, respectively. Under the action of the release heat of nuclear waste, the negative pore pressures both in Case 1 and Case 2 are 1.2-1.4 and 1.01-l.06 times of the initial values, respectively. So, the former represents an obvious effect of pressure solution. The magnitudes and distributions of stresses within the rock mass in the two calculation cases are the same.
A 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 were single,but the seepage field and the concentration field were double,and the influences of sets,spaces,angles,continuity ratios,stiffnesses of fractures on the constitutive relationship of the medium were considered.Also,the relative 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 was 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 the negative pore pressures and nuclide concentrations in the porosity and fracture present different changes and distributions.Even though the saturation degree in porosity is only about 1/10 that in fracture,the flow velocity of underground water in fracture is about three times that in porosity because the permeability coefficient of fracture is almost four orders higher than that of porosity.The value of nuclide concentration in fracture is close to that in porosity.
