Research On The Wide-narrow Juncture Diseases Influence And Maintenance Of CRTS Ⅱ Slab Ballastless Track Under Complex Temperature

Ballastless track and Continuous Welded Rail (CWR) are the key techniques of high-speed railway in China. Among the various systems of ballastless track, CRTS Ⅱ slab ballastless track has been wildly used. Because of the vast area and extreme climate differences, the CRTS Ⅱ slab ballastless track and CWR are subject to complex temperature condition. Existing researches show that under the condition of complex temperature, CRTS Ⅱ slab ballastless track exists a variety of diseases, such as mortar de-bongding, buckling deformation of slab, drawing breakage in wide-narrow juncture, tension failure of supporting layer, especially wide-narrow diseases. Based on the study of CRTS Ⅱ slab ballastless track CWR stress and deformation laws, which under the condition of temperature, the reasons of drawing breakage and crushing on arch in wide-narrow juncture were deeply researched, the influences of two kinds diseases to track stress and deformation were analyzed. Specially, the effective maintenance time and measure were proposed. The main work contents are as follows:(1) Using the methods of birth-death element and restart analysis, on the basis of summarizing the track structure parameters,a good condition CRTS Ⅱ slab ballastless track CWR space fine coupling model is established by the finite element software ANSYS. And according to the diseases characteristics of cracks in joint of slabs and damages in wide-narrow juncture, the damage models of CRTS Ⅱ slab ballastless track structure are established.(2) Based on the track model in good condition, the mechanical properties of ballastless track and CWR are studied under temperature gradient, whole temperature, and even extreme temperature, respectively. The results show that the temperature gradient influences greatly on the vertical deformation of the track slab, but slightly on the stress of the track slab, the mortar layer, and the supporting layer. The overall temperature has great impact on the longitudinal stress of the track structure, while little impact on the vertical stress and the transverse stress. If the whole temperature difference is too large, the longitudinal stress of the slab will exceed the tensile strength of concrete and then the slab is tension failure. Under extreme high temperature, the longitudinal stress of the slab is 23.7MPa, close to the concrete compressive strength. Under extreme cold temperature, the longitudinal stress of the slab is 18.8MPa, exceeds the concrete tensile strength, and then the slab is broken. So the stress and deformation of track structure are so great that damages are possible under extreme temperature.(3) Based on the damage track model with the crack in wide-narrow juncture, impacts of the crack width and depth on track structure are studied under temperature gradient and temperature dropping condition. Results show that the crack depth has great influence, but the crack width had no obvious effects. Under temperature gradient, when the depth of crack is 0.15m, the longitudinal compress stress of the slab is 39.9MPa, exceeds the concrete compress strength. When the depth of crack is 0.2m, the longitudinal compress stress of mortar layer is 23.3MPa, exceeds the ultimate compress strength. Under temperature dropping condition, when the width of cracks is greater than or equal to 0.1mm, the slab and mortar are broken because of their longitudinal stress exceeding the ultimate strength. When the depth of cracks is greater than or equal to 0.06m, the slab and mortar is also broken. So this thesis suggests the depth of crack is used to be the control element, while its values is greater than or equal to 0.06m, the maintenance measure named low pressure injection should be taked in time.(4) Based on the track model with damage in wide-narrow juncture, the focuses are on the reasons of wide-narrow juncture crushing on arch and the influences of wide-narrow juncture damage under high temperature and continuous high temperature. Due to the damage of the wide-narrow juncture, the rail stress increases and deformation aggravates. And the rail vertical irregularity is obvious. Also, some other consequences are attributable to the damage, including the debonding between track slab and mortar layer, the appearance of arch on the track slab and arch spreading to the center plate under continuous high temperature, and the increasing displacement of arch. While the debonding length of totally-damaged wide juncture can reach 1.438m, and the debonding speed increases in the length of 0.87m, the displacement of arch can reach 0.612mm, the relative values for totally-damaged narrow juncture are 1.625m,0.65m, and 1.438mm. The longitudinal compressive stress of damaged wide-narrow juncture becomes larger. When it exceeds the concrete compressive strength, the concrete will be crushed and the damage will be more serious. Therefore, in order to avoid the diseases, the maintenance measures of chiseling and re-pouring concrete should be taked promptly before debonding length reaching 0.65m.