Research On The Influence Of Soil Temperature And Porosity On Stray Current Distribution Characteristics Of Urban Rail Transit

Due to its advantages of "convenience,speed,comfort and safety",urban rail transit has become an important mode of transportation in many large and medium-sized cities.However,while urban rail transit brings convenience,the stray current it generates will also bring huge security risks to the rail system and the safety of maintenance personnel.Aiming at the existing problems in the current research,a method combining experiment and simulation is proposed to study stray current variation trend under different soil temperatures and porosity in this thesis.On the basis of obtaining the influence laws of different soil temperature and porosity on stray current,an evaluation model for the DC interference range of stray currents is established to simulate and predict stray current corrosion.The main works of this thesis is as follows:(1)The stray current distribution model is established based on the traditional resistance distribution network.In the calculation,the analytical formula of the stray current in the soil is solved according to different soil resistivity.Secondly,the stray current experimental test circuit is built,and the experimental results of the two structures of the rail-earth and the rail-drainage network-earth under the single and bilateral power supply modes are compared with the analytical results.The feasibility and correctness of the experimental circuit are verified.(2)Several groups of experimental tests on the influence of soil temperature on stray current in the range of-15～70°C were carried out,and the results were compared with COMSOL simulation results.Under the same soil conditions of unilateral power supply mode,the stray current increases first and then decreases with the increase of temperature.At the same temperature,the stray current value is the largest in loam,followed by in sand,and the smallest in gravel soil.While the DC interference range of stray current in different soil temperatures is inversely correlated with the variation trend of stray current in soil,that is,the DC interference range of stray current decreases with the increase of stray current in soil.(3)The stray current experimental tests and COMSOL simulation of the combination of single-layer and multi-layer soil samples with different porosity are carried out,and the experimental test results and simulation results are compared and analyzed.In the single-layer soil experiment,under the same porosity,the stray current value in loam is the largest,followed by in sand,and the smallest in gravel soil.For the same soil,the stray current increases with the decrease of soil porosity.In the case of adding stones of different sizes,the stray current decreases with the increase of the size of the stones added.In the multi-layer soil experiment,under the same conditions such as temperature and water content,the magnitude of the stray current is mainly determined by the soil and porosity of the upper soil layer,and has an obvious increasing trend with the decrease of the upper layer soil porosity.With the decrease of the soil porosity in the lower layer,it showed a slow increasing trend.The DC interference range of stray current in different soil porosity is inversely correlated with the variation trend of stray current in soil.