The Research On Cracking Of Monolithic Track Bed Of High-speed Railaway And Carbonization Law Of Crack Site In Northwest China

With the rapid development of China Railway High-speed,railway infrastructure projects are continuing in various places in China.Most of the high-speed railways adopt ballastless track structure,replacing the original ballast track with monolithic ballast bed in our country.In the northwest of China,a part of monolithic ballast bed cracked,due to the bad weather environment.The cracks in monolithic ballast bed will not only destroy the integrity of its structure,but also make the CO₂ gas in the air enter its interior,which will case the concrete to carbonate and accelerate the corrosion of steel bars.Those problems will affect the bearing capacity and durability of the whole structure,and leave potential safety hazards for high-speed railway in the operation process.Therefore,this paper takes the cracking situation of the monolithic ballast bed as a main line in Northwest China,and mainly studies the following aspects:?1?Long-term observation,investigation and measurement of the cracking of the monolithic ballast bed in Northwest China are carried out.The distribution and location of the main cracks on the surface of the monolithic ballast bed are introduced,and the cracking width of the eight-shaped cracks is counted in detail.At the same time,the causes and mechanism of the cracking of the monolithic ballast bed are studied and analyzed.?2?In order to study the effect of crack width on the carbonization of crack sites,experiment is carried out to study the carbonization law of crack sites,those cracks possess different widths.In order to control the crack width accurately,the method of embedded copper sheet is used to prepare the specimens.In the process of specimen preparation,the pre-embedding methods of copper sheets with different thickness and the optimum time of pulling out the copper sheet are determined after repeated test and verification.Finally,in consideration of the test purpose and the situation cracks prefabrication in the test,the cracks width of 0.06mm,0.08mm,0.10mm,0.20mm and0.30mm are adopted.?3?By studying the carbonization status of the cracks after carbonization,the carbonization depths of the cracks at different depths were measured and the carbonization laws were summarized.At the same time,the influence of different crack width on the carbonization law of the crack region was studied.?4?In order to study the effect of different carbonization time on the carbonization law and carbonization depth of crack region,the carbonization status of cracks region was studied and analyzed after 7 days,14 days,21 days and 28 days of carbonization.The depth of carbonization on the surface at non-crack sites of specimens,the depth of carbonization at crack sites with the same width but different depths,and the depth of carbonization at the bottom of cracks were compared and analyzed,and the effect of different carbonization time on the carbonization at crack sites was summarized.?5?Based on the law of conservation of mass,the control equation of concrete carbonization is deduced,and the equation is similar to the heat conduction equation.By studying the meaning of each parameters and selecting reasonable parameters,and with the help of the thermal analysis module of ANSYS,a general finite element software,the carbonization of cracked specimens is modeled and analyzed.?6?According to the development of eight-shaped cracks in monolithic ballast bed at sleeper end,three kinds of crack prevention measures were put forward after theoretical analysis and experimental study,and some measures are applied to practical projects.By investigating the effect of those measures in practical engineering,the availability of crack prevention is affirmed.?7?Combining with the relevant provisions on the relationship between crack width and crack repair measures in the daily maintenance of monolithic ballast bed at the present stage,the concept of weighted total crack width is put forward and relevant research is carried out,which provides a theoretical basis for the further improvement of the evaluation criteria for cracks in monolithic ballast bed.