Three-field Coupled Numerical Model For Freezing And Thawing Settlement Of Frozen Soil And Its Engineering Application

In recent years,with the accelerated implementation of the western development and corresponding transportation infrastructure constru,ction,many frost damage problems ca-used by soil freezing and thawing have been encountered in the process of crossing tunnels in cold regions.Therefore,it is of great significance to study the relationship and interaction between the three fields of water,heat and force in frozen soil and to reveal the mechanism of frost damage.Frost heave and thaw settlement are very complex and comprehensive problems.After many years of research by many researchers,the theory of hydro-therrmal-mechanical coupling of frozen soil is relatively complete,and more calculation programs have been developed,but less attention has been paid to the melting process.In this paper,the theoretical framework of frozen soil is established,the appropriate frozen soil model and the calculation method of model parameters are selected.On this basis,the numerical model of frost heave and thaw settlement of frozen soil is established.The reliability of the numerical model is verified by laboratory tests.The numerical model is used to simulate the tunnel,and the stress response of the tunnel support structure is analyzed when the surrounding rock is frozen and thawed,and the sensitivity of several factors is analyzed.The main research results are as follows:(1)When establishing the frost heave numerical model,the equilibrium equation is established by the effective stress principle of frozen soil,the energy conservation equation is established by considering the heat conduction and convection in the freezing process,and the deformation field equation is established by deducing pore rate equation.(2)When establishing the numerical model of melting settlement,the mass conservation equation is established on the basis of neglecting the water migration in the melting process;combining with the mass conservation equation,the energy conservation equation expressed by porosity is establish ed,the location of isotherm is solved,and the range of melting zone is porosity is established,the location of isotherm is solved,and the range of melting zone is determined;and the deformation field equation is established on the basis of considering the decay of soil skeleton resistance to deformation during melting.(3)The reliability of numerical models for frost heave and thaw settlement is verified by laboratory tests.The effects of overlying load,temperature gradient,cooling rate and other factors on the final frost heave are calculated and analyzed.The influence of overlying load and initial water content on the deformation of soil during melting consolidation is analyzed.(4)Based on the background of a loess tunnel and a highway tunnel in cold region,the frost heave and thaw settlement of the tunnel are calculated by using the frost heave and thaw settlement numerical model established in this paper,and the stress response of the tunnel support structure is analyzed.The influence of tunnel burial depth,boundary temperature condition,lining thickness and permeability coefficient on lining in freeze-thaw process of surrounding rock are compared and analyzed.The analytical solution of frost heave force anisotropy of circular tunnel is derived.