Mechanical behavior of train-slab track coupled system under subgrade settlement and earthquake excitation

• Combined subgrade settlement and earthquake excitation significantly amplify dynamic responses of train-slab track systems compared to individual effects. • Short settlement wavelengths (10 m) are particularly critical, causing base-subgrade separation and heightened sensitivity of safety indexes. • Wheel unloading rate and derailment coefficient increase with earthquake intensity, with specific thresholds (0.17g and 0.29g) for a 10 m wavelength and 20 mm amplitude. • The refined numerical model provides a tool for assessing running safety under complex service conditions, aiding in design and maintenance of high-speed railways.