Reliability assessment of interface debonding between <scp>CRTS II</scp> track slab and <scp>CA</scp> mortar

Abstract Interface debonding between the track slab and cement asphalt (CA) mortar layer is a major damage issue in China Railway Track System (CRTS) II slab ballastless track structure in service. This paper investigates the reliability of interface debonding under varying temperature conditions. A limit state function was formulated based on the interface debonding mechanism analysis. A finite element method (FEM) for the CRTS II slab track structure was developed, incorporating a bilinear cohesive zone model (CZM) to accurately represent the interface behavior. By combining the FEM with the univariate dimension reduction‐based point estimation method, the first four moments of the limit state function were obtained. Then, the interface debonding reliability index was calculated using the high‐order moment method. The study explored how this reliability varies with temperature gradients at different positions within the track slab. Finally, the overall debonding risk of the track structure was analyzed. Results show that overall temperature significantly affects the interface performance, though this influence weakens with increasing temperature gradients. Specifically, under overall temperature rise, increasing positive gradients reduce the interface debonding reliability, leading to greater susceptibility at slab centers. Whereas under overall temperature drop, increasing negative gradients result in higher debonding risk at slab corners. Notably, locations 500 mm from the slab centerline and edge exhibit higher interface debonding reliability indices than the points at the slab centerline and edge, respectively. In addition, evaluating only an individual failure mode may overestimate the interface performance. Consequently, the overall interface behavior must be considered for accurate assessment of structural safety.