The Thermo-Hydro-Mechanical Effect On Static And Dynamic Properties Of Soft Soil And Its Application

Engineering technology such as nuclear waste disposal, landfill, ground source heat pump and prefabricated vertical thermal drained consolidation in soft soil foundation has been developed well recently. Moreover, large catastrophic explosion accidents have generated abundant high-temperature high-heat explosion products, which propagate and diffuse in rock and soil to destroy the underground structures. Because of these two reasons, the thermo-hydro-mechanical (THM) issue raises wide concerns and stimulates the rapid development of relevant research.However, the THM effect on rock and soil is related to many disciplines, including permeation fluid mechanics, static and dynamic soil mechanics, and heat transfer theory, and involves multiple complicated factors. All these complicate the comprehensive and systematic research about the mechanism of THM effect on rock soils. For this reason, the property changes (from consolidation to dynamics) of saturated soft soils under the temperature effect are characterized from three aspects:theory, experiment and numeric simulation. The main research contents in this dissertation are listed below.A set of nonlinear thermoporoelastic equations is deduced based on Biot’s consolidation theory and Fourier’s heat transfer theory. This equation set is first degenerated into linear forms. Thereby, the thermal consolidation problems of infinitely-long cylindrical cavity and finitely-long cylindrical heat source both in infinite space are solved as well as the thermal response of saturated soil sample under undrained heating with isotropic confining pressure. On basis of the solutions, the effects of various coupling terms (e.g. the water and soil grain compression, the solid-and fluid-phase sink) and the non-linear item (heat convection) are investigated.Based on THM theory, the thermal response and consolidation problems of the tri-axial test samples under undrained heating or drained heating with isotropic confining pressure are simulated using the finite element software COMSOL. In these simulations, the elastic constitutive model, nonlinear elastic constitutive model and a modified cam clay model considering temperature effect are adopted separately combing thermal expansion coefficient of water with or without consideration of temperature effect. Meanwhile, the corresponding temperature-controlled tri-axial tests are carried out. The analytical and numerical results are also compared with the experimental results. The effects of factors such as Poisson’s ratio, Young’s modulus, the water thermal expansion on the results are investigated and discussed.The mechanism how the heat source in a vertical well accelerates the consolidation in a vertical drain system is investigated by numeric simulation in COMSOL. On this basis, the finite element program TSDSS, which adopts a consolidation constitutive relationship and can simulate the thermal consolidation with vertical drains, is developed. The consolidation constitutive relationship can make up the constitutive model without considering temperature effect, which cannot calculate the settlement increment in thermal consolidation. The relevant model test is carried out to verify the constitutive model and the program.Four types of temperature-controlled tri-axial tests with Ningbo soft clay are performed, including (1) consolidation+undrained heating, (2) drained heating consolidation+undrained shear, (3) consolidation+shear until to reach the target value ofdeviatoric strain+undrained heating, and (4) drained heating consolidation+cyclic undrained shear. The test results as well as the effects of temperature rise on shear strength, pore pressure and deviatoric strain of soft soil are analyzed and discussed. Furthermore, on basis of THM theory, the modified cam clay and the bounding surface constitutive models considering temperature effect are set up, and these models are implemented in FEM software ABAQUS in order to be used to simulate the four types of tri-axial tests.A set of thermo-hydro-mechanical coupled equations for saturated soil dynamic response model (THMD) is established according to generalized thermoelastic theory and Biot’s porous elastic dynamic theory. First, the thermal dynamic response problem of an infinitely-long soil column is solved, and thereby, the effects of various factors on the results are investigated. Second, a thermal dynamic model of infinitely-long cylindrical cavity in infinite space is set up in COMSOL, and the effects of nonlinear terms in governing equations on results are studied by solving the problem in COMSOL. Finally, the wave equations for saturated soil are established on basis of THMD equations. By solving wave equations with numerical approach, the phase velocities and the attenuations of P1-wave, P2-wave and T-wave, and the effects of relevant parameters on wave phase velocities of three compressional waves are investigated.