Study On Hydro-thermal Characteristics Of Engineering Ground In Cold Region Based On Equivalent Boundary Conditions

The study on hydro-thermal characteristics of engineering ground in cold region is the basis for revealing the mechanism of freezing damage and controlling freezing damage.Reasonable selection of boundary conditions is an important prerequisite for accurate and efficient calculation of hydro-thermal field of frozen ground.In this paper,the variable separation method is used to solve the problem of heat conduction in finite media under periodic boundary conditions,the equivalent relationship of boundary conditions is established,and the selection of boundary conditions in calculation is simplified.Rely on the actual project,the distribution rule and influencing factors of water and heat of ground in cold region are analyzed,and the key influencing factors on the hydro-thermal characteristics of frozen soil ground are explored.Finally,the hydro-thermal characteristics of frozen subgrade in road reconstruction projects are studied.The main conclusions are as follows: First,the equivalent principle of boundary conditions proposed can be applied to the determination of boundary conditions in the thermal calculation process of ground in cold region.Secondly,due to the existence of latent heat of phase transformation,the ground temperature at different depths of frozen soil ground changes with time in a sine-like function;Under the same periodic boundary conditions,the temperature gradient and amplitude decrease more rapidly along the depth direction and the influence range of temperature fluctuation is smaller than that without phase change;When the temperature gradually decreases to around freezing temperature,the unfrozen water content will undergo a transitional decrease,but will not decrease to zero.Thirdly,When the surface wind speed varies in the range of 0～5m/s,the maximum melting depth of the frozen soil ground varies greatly;Seasonal surface snow cover will significantly raise the lowest temperature in the annual cycle at the surface boundary,increase the maximum melting depth of the frozen soil ground,and even cause the disappearance of the permafrost underlying the ground.Fourthly,affected by road reconstruction,frost heaving at shoulder position on one side of original subgrade reconstruction will be significantly reduced and water accumulation at each boundary will be more obvious;Affected by the extreme snowfall climate,the frost heaviness of the shoulder position on the reconstructed side will be further increased after the road is reconstructed.