Study On The Effects Of Nonlinear Changes In Permafrost Thermal Parameters And Water Migration On Temperature Fields

Thermal parameters such as the thermal conductivity,specific heat capacity,and latent heat of the frozen soil change nonlinearly under freezing.According to analyzing the development law of frozen soil thermal parameters under different temperature conditions,we can use the normalization method to obtain a function that can describe the change of thermal parameters of frozen soil and the degree of freezing of frozen soil.An empirical formula for the thermal parameters of frozen soil can be obtained through the function.At temperatures below 0 °C,moisture migration occurs within the soil,it causes redistribution of moisture and thermal parameters inside frozen soil,and also affects the development of temperature field in frozen soil.Considering the nonlinear changes of thermal parameters of frozen soil and the effects of water migration,use numerical simulation software ABAQUS to simulate the temperature field under two influence conditions.Comparative analysis with simulation results of traditional temperature field.Consider the impact of moisture migration,this article come up with a more realistic situation,and the calculation method of temperature field of frozen soil with smaller calculation error.This article does the following:(1)It is assumed that the soil particles are orthogonally arranged with each other,and the contact surface of the soil particles is the ball missing contact,thus establishing the soil skeleton model of the equivalent ball lack of contact.In negative temperature environment(T<0?),free water away from the surface of the soil particles first freezes into the ice core,and as the temperature decreases gradually,the ice core eventually develops into an ice skeleton.Based on the difference of the interface effect of heat transfer between soil-water-ice three-phase bodies,a composite thermal transfer physics model of heat transfer in frozen soil is proposed.A composite calculation model of frozen soil thermal conductivity is established according to the composite heat transfer model and soil skeleton model.(2)Based on the temperature parameters of the frozen soil under the test,the change rate of frozen soil thermal parameters under the unit temperature gradient is obtained by analyzing the change of the thermal parameters under different temperature conditions.The change rate of frozen soil thermal parameters is processed by the naturalization method,and the mathematical expression of the change of heat parameter is fitted.And through the function expression can be reversed to obtain the thermal parameters under different temperature conditions.(3)The driving force of water migration in frozen soil consists of the matrix suction of the warm soil and the force between ice water.The driving force of water migration in frozen soil can be solved by the soil-water characteristic curve and the broad Clapeyron equation of unsaturated soil,and the boundary conditions and balance conditions of frozen soil unfrozen water migration in frozen surface can be analyzed by static analysis,and a mathematical calculation to calculate the amount of water migration is established.The effect seamounts of moisture migration on frozen soil thermal conductivity,ratio heat tolerance and latent heat parameters are analyzed and calculated.(4)Based on the nonlinear change of thermal parameters and the effect of moisture migration on frozen soil heat parameters,the single-tube freezing test and the shaft excavation test are designed,and the effect of nonlinear change of thermal parameters and moisture migration on the freezing temperature field is analyzed according to the simulation results.On this basis,based on the effect of moisture migration on the frozen temperature field,the temperature field calculation is modified.