Floor heave failure mechanism of large-section tunnels in sandstone with shale stratum after construction: A case study

The floor heave in high-speed railway tunnels may cause trains to decelerate and even result in accidents. To prevent the occurrence of kickdrum disease, its mechanism first needs to be clarified. In this work, based on field monitoring data, the characteristics of floor heave were analysed, and the boundary conditions were determined experimentally. The effects of various weakening factors and depths on floor heave were analysed using numerical simulations, and the state was categorised into five grades. The results showed that the deformation pressure at the bottom of the tunnel was transmitted to the filling layer through the inverted arch structure, where the deformation pressure originated from the weakening of the surrounding rock. Furthermore, the filling layer was compressed at both ends and pushed toward the bottom, resulting in bending, deformation, and cracking. When the weakening factor was less than 0.5, the deformation and cracking of the filling layer were significant. Moreover, when the weakening depth exceeded the plastic zone, the change in the weakening depth had a weaker influence on floor heave.