A new approach in calculation of heat release during high geothermal tunnels construction considering ventilation time effect

Tunnels with surrounding rock temperatures exceeding 28 degrees C are called high geothermal tunnels. During the construction of high geothermal tunnels, construction personnel health, machine operation efficiency and second lining safety are affected by the heat tunnel. Therefore, calculating the precise heat release characteristics of high-geothermal temperature tunnels is a prerequisite for ensuring the smooth passage of the tunnel. The guideline that states that the wall temperature is constant in the longitudinal direction of the tunnel is not realistic. This constant temperature results in large heat release calculations and leads to increased energy wastage while cooling high geothermal tunnels. Therefore, a method is proposed for calculating the heat release along the longitudinal direction of a tunnel based on a three-dimensional implicit finite-difference technique considering the ventilation time and average wind speed. This calculation method is used to determine the heat release values of the surrounding rock, initial support and second lining and to compare these findings with the guideline algorithm. The results show that the difference between the internal surrounding rock temperature calculated by the three-dimensional implicit finite-difference method and the measured value is 0.94 degrees C, verifying the theory accuracy. The heat release of the initial support section is much higher than that of the surrounding rock and the second lining; all heat release values are smaller than the normative heat release. This method of calculating heat release is more realistic and can effectively lay the foundations for high geothermal tunnel cooling while saving costs. Therefore, the heat release calculation method should be extended and used as a basis for calculating ventilation and cooling in other high geothermal tunnel construction projects.