| The short maintenance intervals and high maintenance costs of ballasted track have led to the emergence of stabilized ballast bed as a relatively inexpensive alternative maintenance solution.The stabilized ballast bed is formed by the solidification of the bulk bed with the infusion or spraying of curing material.Currently,the commonly used polyurethane-stabilized ballast bed has high permanent deformation and poor durability.Semi-flexible material,with open-graded matrix asphalt mixture(void ratio is 20–25%)filled with special cement grouting materials.With high load-bearing capacity and excellent rutting resistance,it has been used in a large number of special road sections such as intersections,bus shelters,parking lots,and gas stations.Due to the excellent resistance to permanent deformation of semi-flexible materials,domestic researchers want to promote the material to be used in stabilized ballast bed,that is,semi-flexible stabilized ballast bed..However,the cracking problem of semi-flexible materials leads to the need to clarify the force characteristics of semi-flexible materials when used in stabilized ballast bed and to conduct targeted research on the mechanical characteristics of semiflexible materials.At the same time,considering the large stiffness of the semi-flexible material,the fastener stiffness needs to be adjusted to make the support stiffness of the semi-flexible stabilized ballast bed in a reasonable range.Firstly,This paper simulates the support stiffness,transverse resistance,and longitudinal resistance of the stabilized ballast bed,and determines the support stiffness of the semi-flexible stabilized ballast bed,and calculates the matching fastener stiffness.A three-dimensional finite element simulation of the cured bed was established to calculate the mechanical response of the track structure under the axle load of the train and to analyze the effect of the curing material,axis distance,and number of axles on the displacement and deformation of the track structure.It was finally determined that the bottom of the semi-flexible curing block was subjected to bending and tensile action.On this basis,this paper focuses on the mesoscopic test and mesoscopic model study for semi-flexible materials and provides guidance for material optimization design of semi-flexible curing roadbeds through sensitivity analysis of different parameters.Secondly,the three-point bending test of semi-flexible materials was conducted,and the whole test process was recorded by the digital camera,and the locations where cracks appeared in all the small beam specimens were counted,and study the crack expansion law of semiflexible materials.The results showed that the most likely location for cracking was the aggregate-asphalt interface,followed by the interior of cement mortar,and the aggregatecement mortar interface,cement mortar-asphalt interface,and asphalt mastic were not easily cracked.Moreover,a mesoscopic heterogeneous model of the semi-flexible material was established to simulate the three-point bending test.The test results were compared with the simulation results to study the influence of the fracture parameters of the components of the semi-flexible material on the overall crack resistance performance.The results show that the higher fracture strength of the asphalt mortar ensures that the semi-flexible material can withstand greater loads as well as loading displacements before fracture.However,after reaching the peak load,the load decreases at a faster rate for smaller beams with higher cracking strengths,indicating that the increase in strength of the asphalt mortar causes the rate of crack expansion to increase.Finally,a method of constructing a mesoscopic heterogeneous model of semi-flexible materials based on random placement and cohesion model is proposed to study the effects of aggregate angularity,aggregate spatial distribution,and porosity on the crack resistance of semi-flexible materials.The results show that the angularity of coarse aggregate affects the crack emergence,evolution,and expansion direction in the local area of the semi-flexible material but has less influence on the overall crack expansion direction.Under the same loading displacement conditions,the maximum tensile stress of the semi-flexible beam containing hexagonal aggregate is greater than that of the semi-flexible beam containing circular aggregate;the semi-flexible mixture with better angularity is more likely to produce stress concentration;therefore,the angularity of the aggregate should not be pursued excessively in the design of semi-flexible materials.The crack expansion path is very sensitive to the spatial distribution of coarse aggregates;Pores in semi-flexible materials have a greater influence on the direction of crack expansion,compared with the aggregate-asphalt mastic interface,the pores in semiflexible materials are weaker,and cracks tend to expand more toward the pores.In addition,porosity has a greater effect on the peak load,the greater the porosity the lower the peak load,3% porosity compared to 7% porosity,the peak load of the small beam increased by 32%;In addition,porosity also has an effect on the displacement to peak load,3% porosity compared to 7% porosity,the displacement to peak load of the small beam increased from 2.0mm to2.4mm.Thus,increasing the grouting rate of semi-flexible materials is particularly important to improve the crack resistance of semi-flexible materials. |
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