| The freezing course of the permafrost sub-grade synthesizes heat exchanging, physical chemistry and mechanics, which is concerned with the complicated interacting process of the temperature field, moisture field and stress field. Both the condition of the heat, the moisture of the subgrade, their changing law and the stress distributing are the key factors to cause the frost damages. Accurately understanding the characteristics of the permafrost, forecasting the heat stabilization status, punishing the frost damage by disposing and improving the moisture, heat condition of the frost, and preventing the damage of the Non-uniform deformation and longitudinal crack guarantee the constructing and developing of the permafrost engineering. First the dissertation generally analyses the developing history of the temperature field, moisture field, stress field and their coupling. Based on the shortcoming that the study on only one of the temperature field, moisture field, stress field is difficult to reveal thoroughly the law of the freezing damage of the subgrade, and to explain rationally the deep reason of all the damages, the research are as follows:1. Aiming at the difference between the permafrost subgrade and the common subgrade, this dissertation formulates the control equation of the non-steady temperature field with phase changing of the permafrost based on the traditional equation. Then the dissertation solves the partial differential equation of the control equation by Galerkin method, analyses the equation with the finite element method by adopting the grid segmentation of the mixture cell in space domain and format segmentation in time domain by the mixture solution of the finite difference.2. This dissertation puts forward an innovation, which is to adopt the large-scale inside test of the temperature field of the permafrost subgrade to simulate the field real environment. At the same time the innovation is validated by the control equation of the non-steady temperature field with phase changing of the permafrost, further the accuracy of the model of the temperature field and the feasibility of the innovation are verified.3. Thinking about the phenomenon that the heat stream and temperature distribution of the permafrost subgrade arise the change of the moving parameter of the moisture in soil, this dissertation introduces the non-isotherm model of the spread flow equation on the basis of the traditional isotherm model of the moisture in soil. Considering that the temperature grads that are consisted of temperature differenceconduces the flow and phase change of the moisture, this dissertation gives out the finite element control equation of the moisture transfer in the permafrost subgrade. At the same time, the dissertation does some research on the law of moisture transfer by the finite element numerical resolution.4. Through the dynamic observation on both the temperature field and the moisture field of the inside soil specimen, this dissertation concludes that the temperature grads is crucial to induce the moisture transfer. Applying the coupling model of the moisture and heat field, the dissertation numerically simulates the temperature field and moisture field of the soil specimen. The simulation validates therationality of the moisture difrusivity concept DT, which is introduced in the controlequation of the moisture transfer in permafrost subgrade. Further the dissertation demonstrates the accuracy of the numerical coupling model of the moisture and heat field.5. According to both the non-stationary phase change temperature field control equation and the moisture transfer control equation in the permafrost subgrade underthe first bound limitation, this dissertation calculates the temperature and moisture field of the section of Qinghai-Tibet highway k3363+800. The compare of the real test values and the calculation proves the preciseness of the coupling model of the heat and moisture field.6. Based on the elasticity theory, the dissertation...
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