Risk modelling and simulation of thermal safety in underground railway tunnel surrounding.

The temperature of surrounding rock of the underground railway tunnel is increasing year by year. This slowly changing thermal hazard not only has a prominent impact on the stability of tunnel surrounding structures, but also deteriorates the tunnel thermal environment, so the formation of the thermal hazard should be investigated. In this work, the thermal hazard model of tunnel surrounding rock was established under the superposition of ground atmospheric temperature wave and tunnel wind flow temperature wave. The corresponding simulation software was developed to estimate the thermal hazards. This dual periodic temperature boundary model (DPTB) was also investigated in comparison with the single periodic temperature boundary (SPTB) model that simplified the periodic ground atmospheric temperature to a constant. The results show that the overlying rock layer of the tunnel is more affected by the superposition of double periodic temperature waves, and its temperature will be significantly higher in autumn. For the calculation example, the average annual heat storage in the surrounding rock under the DPTB is 41,775 kJ/m2, reduced by 432 kJ/m2 compared to the SPTB. The average temperature rise in the shallow surface surrounding rock over 25 years under the DPTB is about 2.04 °C, which is 0.48 °C lower than that of the SPTB. These calculation results provide a reference for the thermal hazards control in underground railway tunnels.