Discrete element modeling of a cross-river tunnel under subway train operation during peak and off-peak periods

In China, a large number of passengers during peak period are a key problem issue that results in a peak load on the subway tunnel. The irregular vibration due to the overloading of train will cause critical damage to rail track and foundations. Due to the lack of field monitoring data, the effects of trainload-induced irregular vibration to the stability of concrete foundation and surrounding area remain a crucial scientific challenge. In current study, a cross-river tunnel in Wuhan subway 2nd line was selected as a case study. The numerical model was developed by using the discrete element method with the consideration of rail track, sleeper, concrete lining, and surrounding strata. Irregular vibration levels induced by train operation with different loads, which included the normal load and peak load, were applied to the rail. Stress, vertical and radial displacement, and particle acceleration in the rail, sleeper, concrete lining, and surroundings were calculated during the numerical simulation. The results revealed that with the increasing of trainload, the settlement of the rail track increases linearly. The symmetrical position on both sides of the concrete lining was compared and showed that the radial displacement and hoop stress of the particles are evenly distributed. The vibrational frequency of the concrete lining was closely associated with the load frequency. The symmetrical trend of radial displacement of particles in the surroundings showed that the value decreased with increasing distance from the outer edge of the lining. The effective distance of train irregular vibration load in the horizontal path is more than 4.0m, which should be considered when an adjacent tunnel is constructed simultaneously.