Research on the matching of tunnel-hoods of high-speed railway tunnels for different lengths at speeds of 400 km/h

The micro pressure wave (MPW) generated by high-speed train at the tunnel exit will produce a certain intensity effect due to the tunnel length ( L t ) raising, which will affect the lives of the residents in the vicinity and the safety of the buildings. In this study, a sliding grid method is utilized to research the MPW generated by a 400 km/h high-speed train through tunnels with different L t . Corresponding tunnel-hoods are tailored to these tunnels, and the computational methodology is validated through field tests. The results show that as the L t increases, the amplitude of the MPW increases first and then decreases, and the intensification rate reaches the maximum when L t is 12 km. The amplitude of the MPW measured 20 m away from the tunnel exit increases by 47.3% compared to the result of a 500 m tunnel; To mitigate MPW of long tunnels, this study proposes tailored tunnel-hood designs for different L t . When L t < 2 km, implementing a equal cross-section hat oblique open-hole tunnel-hood achieves a 67.5% mitigation in the amplitude of MPW; When 2 km < L t < 5 km, adopting an enlarged hat oblique open-hole tunnel-hood can reduce the amplitude of MPW by 70.7%. When L t > 8 km, a combined tunnel-hood with an equal cross-section open-hole and enlarged hat oblique open-hole tunnel-hood effectively mitigates MPW. When 8 km < L t < 12 km, a combined tunnel-hood with an optimized opening rate can be used to mitigate MPW. The results of the study not only provide a reference for the design of tunnel-hood, but also provide new strategies for mitigation of MPW in tunnels of different lengths.