Study on damage propagation of CA mortar layer for CRTS II slab ballastless track under vehicle-induced hydrodynamic pressure

The interlayer damage propagation in ballastless tracks is a critical issue impacting the safety of high-speed railway operations and the maintenance strategies for track structures, making it a key focus of research in ballastless track systems. This study examines the characteristics of interlayer damage propagation in CRTS II slab ballastless tracks under train-induced hydrodynamic pressure. Material property tests were conducted to identify the key parameters of the bilinear cohesive zone model for CA mortar under tensile and shear conditions. A structural-damage-fluid–solid coupling dynamic simulation model was developed to assess the effects of void geometry and water filling levels in damaged areas on train-induced hydrodynamic pressures. Using the zero-thickness cohesive element approach, an analytical framework for evaluating damage propagation in CA mortar layers was established. Damage propagation indices were proposed, and the influence of initial crack conditions at void boundaries on damage propagation was systematically analyzed.The results demonstrate that the fracture behavior of CA mortar can be effectively described by the bilinear cohesive zone model. The maximum dynamic hydrodynamic pressure within voids caused by train loads increases exponentially with the water filling ratio in the damaged region. Dynamic hydrodynamic pressures are most significant near fastener positions where void dimensions approximate fastener spacing, reaching up to 5.45 MPa—exceeding the tensile fracture strength of CA mortar by 79.93 %. This pressure acts as a key driver of damage propagation. Additionally, the potential propagation of void-induced damage correlates positively with the initial crack configuration. The damage propagation state can be quantitatively characterized using indices such as the potential crack propagation length and the total crack propagation length.