Abstract
Drying-induced cracks are an important issue for bi-block ballastless track system consisting of foundation, precast sleepers, and cast-in-place track slab, which not only significantly affects the comfortableness and safety of rapid transit railway but also reduces the service life of ballastless track. In order to explore its damage mechanism, this work presents an evolution model of relative humidity (RH) in the CRTS I bi-block ballastless track system by considering the actual construction sequence and environmental conditions to simulate the crack propagation induced by nonuniform RH field. Firstly, based on the node coupling technique, a three-step transfer process of RH is designed to separately investigate the influence of the construction sequence on the early humidity field in the foundation, sleepers, and cast-in-place track slab, and then the nonuniform distribution of early humidity field in the ballastless track system is determined. Subsequently, the formation mechanism of shrinkage crack in the system is analyzed, and the crack propagation path is predicted by using the mixed-mode fracture criterion. The results show that the maximum relative humidity gradient (RHG) appears at the interface between the track slab and the sleeper after concreting the cast-in-place track slab, which causes the maximum principal stress due to the drying shrinkage property of concrete materials. When the maximum principal stress exceeds the tensile strength of the interface, an interface crack will be generated and converted to a splayed crack with an initial angle of about 45° at the sleeper corner, which will be further propagated under the action of drying shrinkage deformation and finally forms a transverse through-wall crack in the track slab. The simulated crack propagation path agrees with the observed one at the site well, and thus the results are beneficial to understand the formation mechanism of through-wall crack in the track slab and further guide the construction design of the bi-block ballastless track system.
Highlights
Since the operation of Beijing-Tianjin intercity high speed railway in 2008, Chinese rapid transit railway has made a rapid development and remarkable achievement [1]
According to the difference of structures built on the subgrade, bridge, and tunnel, the CRTS I biblock ballastless track can be divided into three types. e schematic diagram of CRTS I bi-block ballastless track in tunnel is shown in Figure 1, which consists of rail, fastener, sleeper, track slab, and tunnel foundation [5]
When the maximum principal stress exceeds the tensile strength of the track slab, the splayed crack with an initial angle of about 45° will be generated at the sleeper corner
Summary
Since the operation of Beijing-Tianjin intercity high speed railway in 2008, Chinese rapid transit railway has made a rapid development and remarkable achievement [1]. To realize the early humidity analysis of the bi-block ballastless track, the following obstacles need to be resolved firstly: (1) after concreting the track slab, the three separated layers of bi-block ballastless track bond to adjacent layers, (2) affected by the construction sequence, the initial humidity field of each layer is inconsistent, and (3) the initial humidity conditions of sleepers and foundation are unknown. En according to the construction sequence, the early humidity field of each layer of bi-block ballastless track was analyzed, and the effects of controlling parameters related to external ambient air drying, internal hydration selfdesiccation, and local wetting time on early humidity distribution in ballastless track were analyzed. E research results can provide theoretical basis for optimizing track structure design and improving track construction technology
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