Abstract: The dynamic response characteristics and cumulative damage characteristics of the base structure under 40 t axle load had not been considered in existing research results in China and abroad, hence, a twodimensional numerical model of tunnelsurrounding rock coupling is established by using software ABAQUS. Based on the cumulative damage mechanism of the surrounding rock and the damage plasticity of the concrete structure at the bottom of the tunnel, the main design parameters of the lining structure at the bottom of the singletrack ballasted tunnel under the load of heavyhaul train with the traveling speed of 120 km/h and 40 t axle load are studied. The results show that: (1) With the increase of train axle load, the surrounding rock at the bottom of tunnel is gradually damaged, especially when the axle load reaches 40 t, the damage effect of tunnel bottom structure is obvious. (2) The variations of the spantospan ratio and the thickness of the filling layer affect the vertical displacement of the inverted arch little; with the decrease of the spantospan ratio, the tensile stress of the inverted arch structure continues increases, and when the spantospan ratios are less than 1∶6 and 1∶7, respectively, the tensile stress of the inverted arch structure increases significantly. (3) With the increase of the thickness of the filling layer, the tensile stress of the inverted arch structure of the tunnel continuously decreases, and when the thickness of the filling layer is greater than 1.3 m, the decreasing trend gradually slows down. (4) Under the condition of recommended key parameters, the fatigue life of the tunnel bottom lining structure can meet relevant requirements.

Key words: heavyhaul railway, 40 t axle load, tunnel bottom structure, dynamic response, damage plasticity