A grading evaluation for transverse interlayer gaps in CRTS III slab tracks based on multivariate indicators

Transverse interlayer gaps in CRTS III slab tracks impair performance and pose significant risks to train safety. It is therefore essential that a reliable evaluation method be established and that targeted maintenance strategies be developed based on defect severity. However, existing classification criteria are often empirical and inconsistent. Numerous and non-uniform evaluation indicators are used, leading to inconsistent grade assessments that hinder effective maintenance decisions. To address this issue, twenty-one potential indicators and their respective limit values were first selected from existing standards for vehicle and track dynamic performance. Subsequently, a dynamic finite element model of the coupled vehicle-track-subgrade system was developed. Through a sensitivity analysis conducted with this model, three indicators—vertical rail displacement, vertical track slab displacement, and tensile stress of the track slab—were identified as the most suitable for damage classification. The effects of gap size and train speed on these key indicators were then systematically analyzed. Based on this analysis, quantitative size limits were established in accordance with a proposed three-grade damage classification principle. To precisely define the control boundaries for each classification grade, fitted function expressions were also developed. Ultimately, this study provides a framework for the maintenance of high-speed railway infrastructure, contributing to improved decision-making and long-term track stability.