Research On The Mechanism Of Subgrade Settlement In Wukui Section Of Lanxin Line Under Speed Increase

In recent years,the scope of speed-up operation of existing railways in our country has been further expanded.The problem of subgrade settlement after speed-up operation of trains has become increasingly serious,which directly involves major issues such as whether the existing lines can maintain speed-up and trains run normally and smoothly.Therefore,it is very necessary to study the mechanism of the existing railway subgrade settlement under the condition of speed increase.In this paper,the main research background is the settlement of the Wukui section of the Lanxin Line under speed-up conditions.Based on the site investigation and test results,the numerical simulation method is used to realize the freeze-thaw simulation based on FLAC2 D.The settlement and deformation of the subgrade under speed-up conditions were studied,and the following contents were mainly completed:(1)Based on the site survey and test results,the basic situation of the diseased section of the Lanxin Line was summarized.The causes of the disease were poor filling properties of the subgrade,moisture migration due to freezing and thawing effects,and increased dynamic loads due to train speed increase.(2)According to the characteristics of the temperature unchanged during the phase transition and the unfrozen water-temperature empirical formula,the water-heat coupling equation is appropriately simplified.The water migration caused by freezing and thawing was realized based on FISH language,and the usability of the method was verified.(3)Analyze the influence of parameters on moisture migration under freezing and thawing,and discuss the effects of soil quality,initial moisture content and temperature difference on moisture migration in soil under freezing and thawing.An improved one-dimensional precipitation infiltration model was established to simulate the subgrade water infiltration under different rainfall intensities in Wukui area,and the changes in the moisture field of the Lanxin line caused by precipitation and freezing and thawing were analyzed.A two-dimensional subgrade model of the Lanxin Line was established,and the water-heat coupling method was applied to the simulation of freezing and thawing of the subgrade in the diseased section.The characteristics of moisture migration of the subgrade under the action of freezing and thawing were analyzed.(4)According to the calculation method of subgrade settlement,the calculation model of subgrade dynamic response was established,and the effects of train speed,subgrade status,subgrade freezing and thawing on subgrade settlement were discussed.On this basis,the foundation settlement of Lanxin line was calculated and analyzed under the condition of speed increase.(5)Summarize the existing subgrade reinforcement methods and give suggestions for the treatment of the settlement.