Study On Variation Characteristics Of Surface Temperature And Heat Flow Of Embankment In Permafrost Regions

With the continued advancement of the“Western Development”strategy and the implementation of“the Belt and Road”strategy,a large number of major projects in permafrost areas such as the Qinghai-Tibet highway are gradually being put on the construction schedule.Therefore,it is urgent to study the balance of surface heat flow and periodic changes in temperature in permafrost regions,reveal the law of the synergistic influence of surface heat parameters and meteorological parameters on the ground temperature,and provide a theoretical basis for scientific regulation of surface heat parameters to reduce ground temperature.The thesis is divided into three parts to study the characteristics of the surface temperature and heat flow of the embankment in permafrost regions.First of all,around the theory of solar radiation absorption,a refined model of the radiation absorption of embankments in permafrost regions was established,which solved the problem of quantitative evaluation of the surface radiation of embankments.Secondly,focusing on the distribution of surface heat flow,a numerical model of heat flow boundary for predicting the temperature of permafrost was created,which can be used to analyze the distribution of typical daily and annual average heat flow on the embankment surface.Finally,it explored the variation law of the hysteresis effect between the surface temperature of the embankment on a typical day and throughout the year and the hysteresis effect of the heat storage G and the surface temperature T_s.It is committed to eliminating the problem of the sunny-shady slope effect and clarified the theory and technology that the sun-slope of the roadbed coated with high reflectivity can eliminate the sunny-shady slope effect of subgrade.Based on these research work,the following three findings have been obtained:（1）The embankment surface solar radiation absorption model solves the problem of quantifying the radiation absorption of the embankment surface in permafrost regions;the macroscopic reflectivity of the simulated solar radiation absorption on the embankment surface is more consistent with the measured value,which verifies the reliability and accuracy of the proposed model.The simulation results indicate that the multiple reflection effects of the embankment slope and the adjacent ground can make the embankment absorb more solar radiation,resulting in macroscopic solar radiation absorption rate of the slope being about 0.01～0.03 higher than the microscopic absorption rate.In addition,even when the surface temperature is close to the phase transition point of frozen soil,the heat flow boundary conditions can well simulate the temperature of the formation.Therefore,compared with the temperature boundary condition,the heat flow boundary condition can more accurately predict the temperature change of the frozen soil layer under the embankment in the permafrost area.（2）Through the numerical simulation of the heat flow distribution process on the embankment surface,it is found that from the typical day and the whole year,the net radiation R_n on the east-west embankment surface lags behind the heat storage G;the annual radiation absorption I,net radiation R_n and convective heat transfer H are similar It has a sinusoidal distribution,and the long-wave radiation L and the heat storage G have small fluctuations.There are obvious hysteresis effects in the heat storage G on the road surface and the slopes on both sides of the southern and northern sides on a typical day and throughout the year.The difference is that the typical day tends to fit the hysteresis curve,and the annual heat storage G is approximately linearly fitted.Through the regulation mechanism of the hysteresis effect between ground heat storage and net radiation,it provides thinking for regulating and controlling the embankment heat storage G.（3）Derived from the hysteresis effect formula,it is found that the heat storage G is affected by the embankment surface reflectivity R,the emissivityε,the sunrise and sunset time difference t_s-t_r,and the maximum solar radiation I₀on the day of t_a,which cools the frozen soil beneath the embankment Temperature provides scientific basis.The temperature change of the embankment surface on a typical day is approximately normally distributed with time,which is consistent with the distribution of heat flow on the embankment surface.However,the time of the temperature peak is later than the heat flow peak,indicating that the influence of the heat storage G on the surface temperature after the heat flow distribution requires a process of transfer and transformation.From the relationship between the heat storage G and the surface temperature T_s,it is found that there is a hysteresis effect on the embankment surface temperature T_s on a typical day and throughout the year.Different from the hysteresis effect of thermal storage G and net radiation R_n,thermal storage G and surface temperature T_s are counterclockwise.It can be seen that the hysteresis model captures the two-way mode of the hysteresis loop obtained by the numerical simulation well.The temperature of the frozen soil under the embankment is mainly controlled by the reflectivity of the ground surface,and other factors only play a minor role.Increasing the reflectivity of the southern side slope of the embankment can effectively alleviate or even eliminate the shady and sunny slope effect of the embankment in permafrost regions.