| The thermo-hydro-mechanical multi-field coupling of unsaturated soil has important application value in many aspects such as deep geological disposal of nuclear waste,design of traffic geotechnical subgrade,and exploitation of geothermal resources.The basic theories involved include thermodynamics,hydrology,and geotechnical mechanics.It is of great scientific significance and engineering value to carry out relevant research work.In this paper,the classical theoretical model of soil water characteristic curve is modified by considering the influence of void ratio and temperature.Based on the law of energy conservation,mass conservation,and momentum conservation,a new thermo-hydro-mechanical coupling theoretical model of unsaturated soil is constructed.Based on the built-in module of the finite element numerical calculation platform COMSOL,the secondary development is carried out,and the coupling theory is embedded to complete its numerical implementation.The numerical calculation accuracy and reliability of the theoretical model are verified by experimental data.The coupling evolution process and internal coupling mechanism of unsaturated soil are revealed by coupling sensitivity analysis and coupling response characteristics under special temperature paths.Considering the theoretical model of material and energy exchange between complex atmospheric environment and soil system,the newly constructed thermo-hydro-mechanical coupling theoretical model is applied to an embankment engineering case in France,and its application and promotion in practical engineering are tried.The main research contents are as follows:(1)The influence of void ratio and temperature on the classical soil water characteristic curve(VG model)is studied by using the method of function shape comparison and parameter influence analysis.These two influencing factors are introduced into the classical VG model by power function and linear relationship respectively,and a modified VG model considering void ratio and temperature effect is obtained.The modified VG model was verified by the existing experimental data,and the effects of temperature and void ratio on the soil-water characteristic curve under different suction ranges were analyzed.Then,the modified VG model is applied to the analysis of unsaturated seepage problems,and the evolution and distribution of water in the ideal embankment under the actual temperature load and continuous rainfall are studied.(2)Considering the established modified VG model,based on the mixture theory and the theory of wet and thermal elasticity,starting from the mass conservation equation,energy conservation equation,and momentum conservation equation of unsaturated soil,combined with the relative velocity relationship,flux density equation,internal heat source constitutive equation,Fourier law,and effective stress principle,the expressions of seepage differential equation,heat transfer differential equation and stress equilibrium equation in unsaturated soil are obtained,and a new complete thermo-hydro-mechanical coupling theoretical model of unsaturated soil is constructed.(3)The finite element numerical analysis platform COMSOL is redeveloped to realize the embedding of the established thermo-hydro-mechanical coupling theory of unsaturated soil,and the numerical analysis program of thermo-hydro-mechanical coupling problem of unsaturated soil is obtained.The specific method is to select the built-in three interfaces of Darcy seepage,porous media heat transfer,and porous elasticity.By introducing parameters and modifying the underlying equation,the water field equation,temperature field equation,and displacement field equation are numerically implemented.The numerical simulation of the existing indoor test is carried out.The numerical solution is compared with the measured data and the average relative error analysis is carried out to verify the accuracy of the numerical prediction of the established thermo-hydro-mechanical coupling theoretical model and the reliability of the calculation process.The thermo-hydro-mechanical coupling response characteristics of unsaturated soil under the action of temperature load path are discussed,and the variation law and distribution characteristics of temperature,saturation,volumetric strain,and displacement are analyzed.(4)The coupling response characteristics of temperature field,moisture field,and displacement field of unsaturated soil under different initial saturation,initial temperature,temperature difference,and gravity effect(including gravity load and different vertical positions)are analyzed.The variation law of three fields under three temperature paths of sudden temperature load,sine function temperature load,and exponential function temperature load is studied,and the influence of different temperature loads on the same physical quantity is compared and analyzed.The relationship between the temperature load type and the soil thermo-hydro-mechanical coupling change is summarized.The sensitivity of specific saturation,temperature,and total displacement in the soil to initial saturation,initial temperature,and temperature difference is studied by the perturbation analysis method,and the sensitivity is sorted.(5)Considering the theoretical model of hydro-thermo exchange in the interaction between complex atmospheric environment and soil system,the newly constructed thermo-hydro-mechanical coupling theoretical model of unsaturated soil is used to calculate the in-situ test of an embankment project in France.The performance of the coupling theoretical model in engineering practice is verified by comparing the field-measured data with the numerical solution,so as to try its application and promotion in practical engineering.Based on the long-term statistical data of various meteorological data in Beijing,a numerical example is designed to analyze the thermo-hydro-mechanical coupling response characteristics of the unsaturated clay embankment under complex meteorological conditions.The research results can provide some theoretical support for the design,operation,and maintenance of transportation infrastructure for the coordinated development of the Beijing-Tianjin-Hebei region. |
