In this study, a novel method for analysing inter-layer defects in slab tracks was proposed, based on fatigue analysis and the extended finite element method. The inter-layer gap of China Railway Track System (CRTS) II slab tracks was analysed. First, a finite element model was established to analyse the stresses in mortar layer under train and temperature loading. Secondly, the results of the stress analysis of the mortar layer were assessed using a fatigue analysis software for calculating the fatigue life of the mortar layer and the areas that fail first. Finally, in an extended finite element analysis, an initial gap was applied over the area that fails first, as determined through the fatigue analysis of the mortar layer. The patterns of the gaps at the ends, in the central part of the edge, and at the corner of the inter-mortar layer were observed and compared. Results show that the new method, which combines fatigue analysis and the extended finite element method, can address the discontinuity problem of the inter-layer slab defects in ballastless tracks, enabling the development process to be simulated. The rate at which the area of gapping increases can be used to characterize the development of the inter-layer gap in slab tracks.

The problem of uneven frost heave deformation of high-speed railway subgrade in seasonal freezing areas seriously affects the service state and service life of slab track structures and threatens the safe operation of high-speed vehicles. Based on the damage plasticity theory of concrete, in this study, an analytical model is established for CRTSIII slab track with damage plasticity and reinforcement. The influences of various frost heaving parameters on track structure deformation, interlayer seam, as well as the stress and damage behaviors were analyzed in detail. The results show that, as compared with a linear elastic model, the damage plastic model better reflects the softening behavior and stress attenuation of track structure concrete after reaching its tensile strength. The deformation and the interlayer seam reach their maximum values when the frost heaving wave peak acts at the position that is one-sixth of the base length from the edge of the concrete base. When the frost heaving wave peak acts on grooves at the base center, initially, the track structure is seriously damaged. The interlayer seam and damage decrease with an increase in frost heaving wavelength and increase with an increase in frost heaving wave amplitude. The interlayer seam of the track structure is more sensitive to frost heave deformation having a wavelength of less than 10 m. The extent of damage to the concrete base gradually increases with a decrease in the wave/amplitude ratio. It undergoes three stages of damage evolution: (i) no damage, (ii) upper surface bending damage, (iii) reverse bending damage. In order to improve efficiency, it is recommended, during track maintenance, to focus on the position of the central groove of the base and the position that is one-sixth of the base length from the edge of the concrete base.