Experimental investigation of the heave behaviors of ballastless railways on expansive soil foundations

Ballastless railways constructed on expansive soils are susceptible to swelling-shrinkage deformation caused by variations in soil moisture, which poses a safety risk for train operations. However, limited investigation on integrated ballastless railway systems in previous studies has hindered the understanding of the heave performance of such railway systems. In this study, a comprehensive testing system at a 1:2 scale for a double-line ballastless railway was developed, encompassing the track slab, subgrade, and expansive soil foundation. A water immersion test was conducted to investigate the influence of foundation swelling on the heave response of the ballastless railway. The results revealed that the heave exhibited a transverse distribution resembling a groove shape, leading to noticeable tilting of the track slab, with a maximum angle of 0.34°, which far exceeded its allowable value. Therefore, it is crucial to pay attention not only to heave but also to track slab inclination when assessing the safety risks of ballastless railways. Furthermore, the underlying mechanisms related to railway heave attenuation and track slab inclination were discussed. During testing, the bulging of steel baffles on the test box induced lateral deformation within the foundation, reducing the swelling pressure and altering the rate of heave growth. By comparing the heave curves with and without the deformation release effect (DRE) defined in this study, it was observed that the DRE significantly mitigated both the heave and inclination of the track slab, with reductions of 18.1% and 26.3%, respectively. Therefore, uniformly distributing reduced-swelling holes within foundations is recommended as a potential measure for alleviating deformation issues associated with ballastless railways on expansive soils.