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• Obtained the mechanism of pressure wave variation under different geothermal distributions. • Studied and summarized the influence of different geothermal distributions on the pressure wave peak. • Obtained the variation law of the dynamic temperature field in the tunnel. In this paper, experiments and numerical simulations are used to study the pressure wave transient laws, propagation characteristics and dynamic temperature field changes in tunnels located near geothermal hot springs. To simulate different temperature distributions, areas of 0–80 m, 80–160 m, 160–240 m and 270–350 m are heated, and the tunnel pressure wave peak value and train surface pressure wave peak value are studied accordingly. The research shows that when the heating zone is 0–80 m, the influence on the initial pressure wave is the greatest, the change rate is 8–10 %, and the initial expansion wave change rate is 5–10 %. When the heating zone is 80–160 m, there is little change in the pressure wave peak value in the first and second stages, and the expansion wave peak value is larger than the normal temperature in the third stage. When the heating zone is 160–240 m, the change rate of the pressure wave peak is small. When the heating zone is 270–350 m, there is a negligible change in the initial compression wave and expansion wave peaks in the first and second stages, and the change rate in the third stage is 2–4 %. Moreover, the heating zone located in front of the tunnel has a greater impact on the pressure at the tip of the train's nose, and the heating zones located in the middle and end of the tunnel have little effect on the initial positive peak value of the train pressure wave but a greater effect on the negative peak value. This study explores the influence mechanism of different geothermal distributions on pressure waves, which can provide more accurate boundary data for improving passenger comfort and the train thermal structural performance in high-temperature tunnels. [ABSTRACT FROM AUTHOR]

• Study the mitigation effect of pressure fluctuations caused by train intersection in a tunnel with the enlarged end. • Consider the effects of the total length of tunnels and unit number of trains on the optimal length of the enlarged section. • Analyse the mitigation principle of the pressure fluctuations impacted upon trains. • Obtain an optimal length coefficient to attain the maximum mitigation of the pressure fluctuations. Intense pressure fluctuations generated by the intersection of high-speed trains (HSTs) in a tunnel are unfavourable for the comfort of passengers and the safety of HSTs and tunnel facilities. This study numerically investigated the mitigation principle of the pressure fluctuation impacted upon HSTs using the enlarged tunnel end with taking into account the total tunnel length and the unit number of HSTs. Moving model tests were also performed to validate the numerical method based on the unsteady RANS equations and RNG k - ε turbulence model. The numerical results show that the enlarged end of a tunnel can manifestly alleviate the negative pressure induced by the train intersection and the length ratio of the optimal length of the enlarged section to the total length is in the range of 0.26–0.28. The optimal length of the enlarged section can be implemented by synchronising the contact of the derived waves with the train intersection. Moreover, the increase in the marshalling number of HST augments the mitigation effect of the enlarged section. This study gives insight into the mitigation of the pressure fluctuation in tunnels and can provide valuable data and a theoretical basis for the tunnel design when considering the aerodynamic effect of HST intersection. [ABSTRACT FROM AUTHOR]