Research On The Prevention And Control Measures Of Frost Heave Flow And Heat Coupling Of Subgrade In Cold Regions

In China,the area of seasonal permafrost is about 5.13 million square meters,more than half of the land area,and a large number of national key projects are distributed here.Traditional measures to prevent and control seasonal subgrade diseases revolve around improving soil quality,controlling moisture,and improving ventilation,such as increasing the height of the stone layer,adding ventilation pipes,setting heat pipes,adding insulation layers,etc.,but due to the inability to isolate the impact of groundwater and atmospheric rainfall,such measures cannot solve the problem of heat balance,lack of active regulation of heat transfer,is a low-efficiency passive measure.Therefore,there is an urgent need for an effective prevention and control measure to solve the safety of frost heave in the roadbed.Based on the ground source heat pump technology,steam refrigeration cycle as the working principle,the use of shallow geothermal energy as a renewable energy,the development and design of a roadbed special heating device;and then with the Lanxin line as the research background,the COMSOL Multiphysics finite element software is used to realize the numerical simulation of the temperature change of the device and the surrounding soil.This paper yields the following research results:(1)Based on ground source heat pump technology and heating technology,a special device for heating permafrost roadbed is proposed.The maximum heat supply coefficient COP of the device can reach 2.8,the average heat supply coefficient COP is 1.1,and the optimal outer diameter of the heat supply pipe is d=31.317mm;on this basis,three directions for subsequent optimization of the device are further proposed: first,combine variables Δt and dimension l are the optimal calculation for the length of the coil in the heating section;the second is the optimization of the structure of the additional gas-liquid separator;the third is the setting of the intermittent mode of start and stop of the device.(2)The simulation results indicate that running under different frozen soil environment(-5 ° C,-15 ° C,-30 ° C),the instructor thawing radius is 4.1m,2m,1.8m,and the vertical thawing radius is 2m,1.3m and 0.7m,play a role in stabilizing the "heat source";the heat dissipation speed of the upper heating section is greater than the temperature absorption speed of the heating section,and the device is only applicable to the frozen soil environment with a freezing soil temperature of-30 ° C.It runs at the same frozen soil environment(-5 ° C),the maximum heating temperature of the device can reach 90 ° C,the average heating temperature is 70 ° C,and the heating section temperature decreases as the depth increases.The radial distance increases and decreases;the lower tube of the device is completed at 45 minutes.The first initial gasization is completed at 45 minutes.The minimum thermal set is-6 ° C,the average heat set temperature is-2 ° C,and the heating collection is heating.The vertical temperature of the section is roughly following the initial distribution temperature of geothermal geothermal,that is,increased with the increase of depth.(3)Simulation indicates that in the same frozen soil environment,when the working quality flow rate is 0.4m/s,0.8m/s,1m/s,2m/s,the soil thawing rate Increased,on the other hand,long-term maintenance of high flow rates will also increase the power consumption.(4)The simulation indicates that the gas liquid separator can be significantly separated after 20 s.In the later stage,it can be combined with the component to improve the heat dissipation efficiency of the second layer of the tube.