Study on the mitigation effect of a new type of connected structure on micro-pressure waves around 400 km/h railway tunnel exit

This paper aims to study a new connected structure composed of parallel headings and cross passages, mitigating micro-pressure waves (MPWs) at the 400 km/h railway tunnel exit. The numerical method based on the sliding mesh method with the RNG k-ε turbulence model is utilized to simulate the relative motion of the train and tunnel, of which the accuracy of the method is verified by moving model tests. Then, the paper analyzes the effects of the distance of cross passage to tunnel entrance (l1), length of cross passage (l2), number of cross passages (n), spacing of cross passages (l3), and layout location on MPWs. For one cross passage, as the increase of l1, MPWs gradually decrease, reaching an optimal value at l1 = 25 m, but as the increase of l2, MPWs gradually increase. When l1 = 25 m, l2 = 10 m, MPWs are reduced by about 34.4%. For multiple cross passages, when n = 2, the reduction rate of MPWs reaches a stable level of about 40%. l3 does not significantly affect MPWs. The connected structure placed at the tunnel entrance is more effective in mitigating MPWs. In addition, we find that the combination of the connected structure and a hat oblique tunnel portal can reduce MPWs by 52%. This study makes reasonable use of the parallel heading left by the tunnel construction to significantly alleviate MPWs without increasing the construction cost.