Study On Distribution Of Material Softening About Double-block Ballastless Track Under Water Environment

During long-term service of double-block ballastless track,the track structure inevitably shows the problem of separation between layers.In the areas with rich rainfall or improper drainage,the long-term soaking of water will change the mechanical properties of cementitious composites,seriously weakening the integrity and stability of the track structure.Therefore,to study the distribution of moisture field and the microscopic analysis of the material properties about the double-block ballastless track under water environment,and to explore the cause and degree of the material softening phenomenon are of great significance for clarifying the development mechanism of the water-induced damage of the ballastless track and perfecting the ballastless track design theory and maintenance method.This thesis presents a series of theoretical derivation and model calculation for the softening of double-block ballastless tracks under water environment.The main research contents and results are as follows:(1)Basing on inducing and classifying the on-site investigation results of existing railroad,the damage mechanism of water-induced damage about ballastless track is further clarified.At the same time,the formation process and damage of each damage are analyzed.(2)The similarity between wet diffusion and heat conduction is verified.The main functions and basic principles of ANSYS thermal analysis are introduced.By establishing the humidity field model of the concrete specimen,a finite element analysis method of concrete humidity field is proposed.(3)Through the calculation and study of the humidity field in the section of CRTSI double-block ballastless track with inter-layer crack on the subgrade,it is found that there are obvious moisture gradients inside the track structure,and the humidity distribution is uneven.The time to increase the internal humidity of structure has a certain lag to the submerged surface.Short time immersion will only affect the surface of concrete materials.With the increase of soaking days,the influence scope will gradually expand to the interior,but it will have little effect on the main structure.The boundary condition plays a decisive role in the humidity distribution of track structure.Inter-layer cracks greatly increase theinfluence range of the submersion,and the crack depth influences the structural humidity field more than the opening amount.(4)The relationship between porosity and the effective tensile strength of wet concrete is deduced from a point of microscopic view,and the influence of the presence of water environment on the structural porosity is explored from two aspects: the dynamic model of porosity change in porous media and the material erosion.