CRTS Ⅲ slab ballastless track is a high-speed railway track structure with completely independent intellectual property rights in China. The use of this type of track structure reduces the risk of high-temperature seam disease at the weak position of the track–interlayer interface to a certain extent. Because of the objective difference between the initial state and the design theory state of the ballastless track structure after construction, the influence of the initial state difference change on the service performance of the interface between the layers of the track structure during the operating period needs to be investigated.

Based on the concrete rebound test, the mechanical state of each layer of the CRTS Ⅲ slab ballastless track was tested. Based on the measured values of the concrete strength of each component of the track structure, the initial difference deviation of the track structure is quantified. Based on the initial difference quantitative data of the track structure and the high-temperature monitoring data of the track slab surface, combined with the ANSYS general finite element software, the spatial simulation analysis model test of the CRTS Ⅲ slab ballastless track was designed. Moreover, the influence of the initial state difference change on the service performance of the track–interlayer interface of the track structure during the operating period was analyzed.

The sampling test results of the initial mechanical state of each layer of the track structure after construction showed that, on the new unoperated line, the measured values of the concrete strength of the track slab and the self-compacting concrete layer have an initial difference deviation of −1.30%–7.42% and −9.98%–2.79%, respectively, compared with the design values. Combined with the initial difference quantitative data, the spatial simulation analysis test model of the CRTS Ⅲ slab ballastless track is established. The analysis results showed a deviation from the original design intention, which will not be conducive to the bonding of the interface. Especially when the strength of the self-compacting concrete is high, the transfer of interlayer temperature force is limited, and the interface damage area increases by 95.65% under adverse load.

The deviation between the initial state of the track structure after construction and the original intention of the design cannot be avoided, which leads to the unfavorable bonding of the interface. The high strength of the self-compacting concrete should be avoided during construction, and different from other ballastless track structures, gap disease at the edge of the slab can be easily induced. For the maintenance and repair work of the CRTS Ⅲ slab ballastless track during the operating period, the idea should be adjusted to supplement and check the service status of the track–interlayer interface corresponding to the limit block.

A ballastless track slab in service is repeatedly subjected to multiple cyclic loads, thereby becoming prone to issues such as decreased structural load-bearing capacity and fatigue failure under such conditions. These problems can seriously endanger the safety of train operations. Therefore, the remaining load-bearing capacity of track panels must be quantitatively characterized under service conditions.

Based on the theory of concrete plastic damage, experiments and analyses were conducted to assess the actual damage to track slabs. Using the temperature field of the track slab and the monitoring data of the wheel-rail force, a load spectrum was fitted to design a fatigue test under the coupling effect of temperature and dynamic load. A rigid cushion block with reasonable stiffness was arranged at the lower end of a prefabricated steel beam according to load requirements, which was used to ensure that the vertical load of the testing machine could be evenly distributed to the point of action of the track slab. Four-point bending and tensile tests were conducted on the track slab to obtain residual deformation and mid-span deflection at different stages. The evolution characteristics of plastic damage and bending bearing capacity under fatigue loads were quantified.

The study found that multifield coupled fatigue effects cause plastic damage to the ballastless track slab, leading to continuous deterioration in its bending bearing capacity. After unloading, the mid-span of the track slab could not return to its original position, indicating some residual deformation. As the number of coupled load cycles increased, both the residual deformation and mid-span deflection of the track slab showed an upward trend. This indicates that internal damage within the track slab is gradually intensifying, leading to a decrease in overall bending resistance. After coupling with cyclic loads, the residual deformation of the track slab at mid-span increased from 0.048 mm to 0.051 mm, marking a 6.25% increase compared to the initial residual deformation. The mid-span deflection of the track plate increased from 1.645 mm to 1.766 mm, which is a 7.36% increase compared to the initial displacement. These changes indicate a 6.85% decrease in the overall bending bearing capacity of the track slab.

The residual plastic deformation of the track slab serves as a macroscopic characterization of internal damage. The gradual increase in plastic deformation with the number of load cycles indicates a deterioration in the actual load-bearing performance of the track slab. The increasing mid-span deflection further confirms the degradation of the actual bending bearing capacity. The overall performance deterioration of the track slab under service conditions would inevitably lead to changes in structural stress and deformation characteristics. In actual maintenance and repair, special attention should be paid to the actual state of weak positions in the ballastless track slab, and reasonable reinforcement measures should be adopted.