Study On THM Coupling Theory Of Soil Freezing And Application

In frozen soil engineering,the freezing of soil often leads to the destruction of roadbeds in cold region and the fracture of deep shaft freezing pipes.During the freezing process,phenomena such as heat transfer,pore water migration and phase change,deformation and failure occurred in the soil,and the water migration is affected by the pore structure characteristics of the soil.Therefore,combining the soil structure characteristics to establish a multi-field coupling theory model of soil freezing can accurately reveal the law of water migration during the freezing process,which has important scientific significance and engineering value.This article comprehensively uses experimental testing,theoretical analysis,and numerical simulation research methods to study the freezing process of soils,and thoroughly explores the thermalhydro-mechanical(THM)coupling mechanism in the freezing process of soils.The ice separation criterion THM coupling model and the dual-porous medium THM coupling model were established to provide better theoretical guidance for frozen soil engineering.The following results have been achieved through the research of this study:(1)The soil samples were subjected to freezing experiments at different freezing temperatures,and the frozen soil samples were subjected to MIP test and SEM test.The experimental results show that the lower the freezing temperature,the higher the porosity of the frozen clay;the pore structure of frozen clay presents the characteristics of double pore distribution,and the decrease of freezing temperature promotes this pore characteristic of clay,and the fractal dimension of pores is also larger;the lowering of the freezing temperature makes the cemented microparticles within the clay aggregates separate from each other,and the internal pores of the aggregates are more abundant.(2)According to the pore ice pressure criterion,a new criterion for the formation of segregated ice is established;a THM coupled freezing theory model based on the criterion of soil ice separation is established,and the model is verified by experimental results and numerical calculation results.The model is used to study the influence of soil characteristic parameters(initial porosity,hydraulic conductivity,thermal conductivity of soil particles)on the freezing process,The results show that the amount of frost heave when the soil is frozen increases with the increase in hydraulic conductivity and thermal conductivity,and the final freezing depth is mainly affected by the temperature at both ends of the soil;the slower the soil freezing rate and the higher the hydraulic conductivity,the easier it is for pore water to accumulate and the formation of ice lenses.(3)Based on the characteristics of soil microscopic pore structure,a dual-porous medium THM coupling freezing model was established,and the model was verified by experimental results and numerical calculation results.The simulation results of the freezing wall show that the area of middle circle where the freezing pipes are arranged densely first forms a closed freezing circle.However,due to insufficient pore water supply,the water content at this area after freezing is lower than that of the inner and outer circle pipes area.After the frozen wall is formed,it thickens at a uniform rate as the freezing progresses.During the freezing process,frost heave occurs due to the migration and phase change of water,and the freezing pipe has a radial displacement outward,and continues to increase at a slow speed after the formation of the freezing wall.(4)The influence of ground parameters,freezing pipe layout and freezing temperature on the freezing pipe subjected to ground shear was studied.The results show that the shear stress on the frozen pipe increases linearly and exponentially with the linear increase of the difference in permeability and thermal conductivity between grounds.At the same time,reducing the number of single-circle freezing pipes and increasing the arrangement of the ring can reduce the shear stress of the freezing pipes due to the difference in soil layers.The paper has 48 figures,16 tables and 113 references.