Effect Of Soil Heat And Moisture Transfer On Stray Current Distribution Of Urban Rail Transit In Lanzhou

Due to its advantages of fast speed,large passenger volume,high energy utilization rate and green environmental protection,urban rail transit can effectively alleviate urban traffic congestion and improve people’s travel efficiency.The stray currents generated during the operation of rail transit can corrode buried metals,pipelines and other facilities,which will become a huge hidden danger for the safe operation of trains.The formation structure and physical properties under the track are closely related to the distribution of stray currents,so studying the influence of heat and moisture transfer on the distribution of stray currents in the formation under the track under different climatic conditions has important engineering practical significance for ensuring the safe operation of trains.In this paper,experimental and numerical simulation methods were used to study the variation of stray current with soil heat and moisture transfer under different meteorological parameters in summer and winter.The main work is as follows:(1)A stray current experimental test platform was built to test the changes of stray current with soil temperature and humidity under three soil conditions of winter loam,sand and gravel soil.Subsequently,a three-dimensional model of the same scale was constructed based on the size of the experimental model to check the reliability of the COMSOL simulation calculation method.The results show that the average relative error and maximum relative error of soil moisture content are 2.93% and 4.43%,the average relative error and maximum relative error of soil temperature are 2.10% and 8.21%,and the average relative error and maximum relative error of stray current are 7.40% and 13.23%,respectively,and the analog values are in good agreement with the experimental values.Therefore,the results obtained by the above numerical calculation method are reliable and can be used for subsequent simulation analysis of layered soils.(2)Under the conditions of 9 soil temperatures and 4 moisture content,the resistivity of loam,sand and gravel soil was tested.The results show that the relationship between the resistivity of loam,sand and gravel is as follows: sand soil> sandy soil > loam.The resistivity of the three kinds of soil decreased with the increase of soil temperature and moisture content,among which,because the resistivity was mainly affected by the moisture content,the resistivity of sand and gravel soil increased most significantly with the decrease of moisture content.(3)Loam A,Sand B and Sand and gravel C were arranged from top to bottom,and the influence of soil heat and moisture transfer on stray current was numerically analyzed under summer and winter meteorological conditions.The results show that the soil stray current decreases with the decrease of moisture content in summer and winter,and the stray current increases slightly when the soil temperature increases greatly and the moisture content decreases smallly.Compared with summer,due to the small evaporation of soil liquid water in winter,the moisture content decreases less,resulting in the slowdown of soil stray current decline.In summer and winter,the stray currents of monolayer soil are as follows: A>B>C.Compared with single-layer soil,the type of soil in the lowest layer of double-layer soil changes,the value of stray current changes significantly,and with the increase of resistivity of the underlying soil,the stray current decreases.Compared with the double layer soil,the change of the type of the bottom soil of the third layer of soil has little effect on the stray current.Therefore,in practice,the corrosion degree of stray currents in the soil on buried metals can be reduced by increasing the resistivity of the lowest soil of the double-layer soil.(4)Under the meteorological conditions of summer and winter,the influence of heat and moisture transfer on current density of loam,sand,gravel soil and its layered soil at different depths was numerically studied.The results showed that the soil current density decreased with the increase of depth,and the decrease was obvious.When the soil depth reaches-30 cm,the current density value and fluctuation range are small.At different depths,the relative relationship between the current density of monolayer soil was A>B>C.At a depth of-10 cm,for double-layer soil,the change of resistivity of the lower soil in summer and winter had a greater effect on the current density value of the upper soil,and when the sand and gravel soil was the first layer,the change of the lower soil had little effect on the current density value of the upper soil due to its large resistivity.For three-layer soils,changing the type of the lowest soil had little effect on the current density value of the topmost soil.At depths of-20 cm and-30 cm,due to the change of soil type around this depth,soil resistivity changes,which directly affects the current density of double-layer and three-layer soil,so in summer and winter,the current density of three-layer soil is greatly affected by the soil type around this depth.(5)In order to explore the main factors affecting the current density,the entropy weight method was used to analyze the influence of temperature and moisture content on the current density of loam,sand,gravel soil and their layered soil at different depths in summer and winter.The results show that at a depth of-10 cm,the variation of summer moisture content is large,and the soil moisture content of different stratification types is the main influencing factor of current density,and the moisture content weight coefficient is the least 54%.The variation of moisture content in winter was small,and the influence of soil temperature on current density of different stratification types increased compared with summer,and the difference between influence weight and moisture content was small.With the increase of depth,its influence on the current density gradually decreases due to the decrease of the amplitude of the moisture content.At a depth of-20 cm,the influence of temperature on the magnitude of current density increases in winter and summer for all layered types of soils.When the depth of-30 cm is reached,the moisture content is basically unchanged,and the soil temperature is the main influencing factor of current density.The soil temperature and moisture content below-30 cm depth are almost unchanged,and the influence on the current density is very weak.