Study On The Influence Of Aggregate Characteristics Of Truck Escape Ramp On The Stopping Process Of Uncontrolled Vehicles Based On Discrete Element Method

Truck escape ramp(TER)is important safety facilities for improving traffic safety on long downhill sections,with the most common being arrester bed type truck escape ramp.The key to their research lies in the design of arrester bed aggregates.Because of the relatively short introduction of the truck escape ramp in China,the research on the impact of aggregate characteristics on the stopping process of uncontrol vehicles is not yet in-depth.Therefore,this paper conducts a study on the impact of aggregate characteristics of the truck escape ramp on the stopping process of uncontrol vehicles based on the discrete element method.It is hoped that the research results can provide a theoretical basis for the design of the arrester bed aggregates and provide engineering application suggestions for aggregate drainage and accumulation.It is expected that the results of this study can provide engineering application suggestions for the later maintenance of aggregates.The specific research content and results are as follows:(1)A study on the impact of aggregate characteristics in the truck escape ramp on the stopping process of uncontrol vehicles under pollution-free conditions.Firstly,based on the analysis of the stopping process of uncontrol vehicles on the truck escape ramp,the discrete element method is used to establish a Discrete Element Model(EDM)for the stopping process of out of uncontrol vehicles in the absence of aggregate pollution;Secondly,conduct calibration tests on the characteristics of aggregates under pollution-free conditions,taking aggregates within the range of 0～40mm as the research object.Through the settlement test of aggregate pressure plates,study the relationship between vertical load and settlement of aggregates with different particle sizes and unevenness.Use the settlement test of aggregate pressure plates to calibrate the aggregate model.On this basis,carry out numerical simulation of the stopping process of uncontrol vehicles on aggregates with different particle sizes and unevenness.The numerical simulation conclusion shows that the stopping distance of uncontrol vehicles on aggregate PST1(Particle Size Test1),PST3,NCT2(Non-uniformity Coefficient Test2),and NCT3 differs from that of PST2 by 3%,36%,12%,and 35%,respectively.The smaller the aggregate particle size and non-uniformity coefficient,the better the blocking performance.Through comprehensive comparison,it is concluded that PST2 is the optimal aggregate grading.Finally,the constant head permeability test and direct shear test are carried out for PST2 aggregate,and according to the test results,the drainage and accumulation engineering application suggestions of aggregate under non pollution conditions are given respectively.Suggestion for the application of aggregate drainage engineering:There is no need to build an additional drainage channel in the middle of the arrester bed.To ensure that the rainwater discharged from the aggregate can be discharged beyond a safe distance,and to prevent rainwater around the truck escape ramp from carrying soil and other substances into the aggregate,the drainage channel should be set at the shoulder positions on both sides of the truck escape ramp;Suggestion for the application of aggregate stacking engineering: The maximum slope of the arrester bed in the truck escape ramp should be maintained within 20 °,and the aggregate PST2 can meet the stacking performance requirements.(2)Research on the impact of aggregate pollution characteristics on the stopping process of uncontrolled vehicles in truck escape ramp.Firstly,using silty cohesive soil as a typical pollutant,study the reasons for the pollution of the aggregate in the truck escape ramp.Secondly,establish a discrete element model of the runaway vehicle stopping process under the characteristics of aggregate pollution.The aggregate model was calibrated by biaxial compression test,real vehicle test and direct shear test.On the basis of calibration experiments,carry out numerical simulation of the stopping process of uncontrol vehicles on aggregates with different levels of pollution.The results indicate that the stopping distance of uncontrol vehicles increases with the increase of soil content in the contaminated aggregate.When the soil content in the contaminated aggregate is less than 15%,the increase in stopping distance of uncontrol vehicles is within 5%.When the soil content is between 20% ～25%,the increase in stopping distance of uncontrol vehicles exceeds 20%.When the soil content is between 30% ～35%,the increase in stopping distance of uncontrol vehicles exceeds 50%.Finally,based on the above research results,suggestions for the application of aggregate maintenance engineering in the later stage are given.When the soil content in the contaminated aggregate is between 0% ～15%,the aggregate is in good condition and does not require maintenance.When the soil content in the contaminated aggregate reaches 20% ～25%,in order to prevent further changes in the state of the aggregate,it is necessary to promptly loosen and renovate the aggregate at this time to avoid further degradation of the performance of the truck escape ramp.When the soil content in the contaminated aggregate reaches 30%～35%,It is recommended to screen out the aggregate or replace the new aggregate.