Study On Low Temperature Response Of Asphalt Concrete Structure Under CRTs ? Type Ballastless Track

Dense gradated asphalt concrete as the waterproof seal layer of ballastless track has the characteristics of waterproofing,damping,vibration absorption,deformation adaptation and construction convenience,etc.The current research on railway asphalt concrete substructure focuses on the mechanical response under load and the effectiveness of waterproofing and drainage.And,asphalt concrete presents the brittle characteristics in low temperature environment so that it is easy to appear crack phenomenon.Therefore,to provide theoretical support for structural design optimization,it's necessary for the structure to study the distribution of temperature field and temperature stress field in cold weather.First of all,based on the theory of temperature field,this paper determined the boundary conditions of temperature field of the track structure.And combined with the feature of track structure of Beijing-Zhangjiakou High-speed Railway,this paper used ABAQUS finite element software to set up field numerical analysis model of the track structure.And this paper used the tested temperature monitoring data of XuzhouLanzhou High-speed Railway in the test section of asphalt concrete to verify the reliability of the temperature field model.Secondly,based on the historical meteorological data of the area where the BeijingZhangjiakou High-speed Railway is located,the temperature field distribution law of the structure under cold weather was analyzed by using the temperature field model of the track structure.And the influence of different solar radiation,different wind speed and different weather seasons on the track temperature field was considered.Finally,based on the thermal-structure coupling method,the thermal stress field numerical analysis model of track structure was established.And the strain distribution law of asphalt concrete covered by the base plate under the most unfavorable negative temperature gradient was analyzed.Then,the influence of different thickness of asphalt concrete layer,different linear shrinkage coefficient and the setting of different length "sliding zone" between base plate and asphalt concrete layer on the strain distribution of asphalt concrete layer was considered.At the end,this paper put forward some suggestions for the design of the track structure.The surface strain values of asphalt concrete layer under different factors was fitted by the orthogonal method.The results show that it is reliable to use finite element software to simulate the temperature field of the structure.In the low temperature environment,the temperature variation of shoulders and middle part of asphalt concrete layer is similar to that of air temperature,while the temperature variation under the base plate is not obvious.And the influence of the environment change on the structure temperature in a single day is mainly within the range of 0.4m depth.Solar radiation and wind speed mainly affect the temperature of shoulders and middle part of asphalt concrete layer,but have little effect on the part under the base plate.Under the most unfavorable negative temperature gradient,the upper track structure will be warped and deformed.So that part of the asphalt concrete layer under the base plate exists ‘strain concentration' at the expansion joints of the base plate,which is the weak link of the structure.The thickness of asphalt concrete layer and the change of linear shrinkage coefficient have little effect on the attenuation of concentrated strain,while the setting of "smooth zone" has a significant attenuation effect on the concentrated strain.In this paper,it is suggested to set 1-2m geosynthetic materials or stress absorption layers on both sides of the expansion joints of the base plate.