Study on generation and evolution of base voids in heavy-haul railway tunnels using particle flow method

Most existing freight railway tunnels have experienced basement cracking, damage, and even mud-pumping after a certain period of operation. For heavy-haul railway tunnels with high traffic densities, large capacities, and large axle loads, this situation will be more serious. This paper establishes a simplified model of a single-track heavy-haul railway tunnel using the two-dimensional particle discrete element method. The meso-evolution process of the concrete structure and surrounding rock void at the bottom of the tunnel is studied in the later stages of repeated loading by heavy-haul trains. The difference in the base void between waterless and watersaturated bases is compared. The cracks in the surrounding rock are first generated at the lowest position of the invert center, and run from the middle to the sides and from the top to the bottom. The terminal cracks return to the free surface, exhibiting a parabolic shape that opens upward. There are more cracks in the middle and fewer at the sides. The asynchronous deformation of the surrounding rock and the inverted arch is positively correlated with the number of cracks. The voiding process under water-saturated conditions is similar to that without water, but the depth and width over which the rock mass is crushed and the range of voiding increase exponentially in the water-saturated case, and the void appears earlier. It is anticipated that these research results will contribute to the structural design and operational safety of heavy-haul railway tunnels.