Temperature Field Of The Surrounding Rock And Air Temperature Distribution In Tunnels With High Geothermal Temperature

In the context of the rapid development of railway tunnels in recent years,the high geothermal problem caused by deep buried long tunnels has attracted special attention from the tunnel community domestic and overseas.An important prerequisite to deal with the problem of high geothermal temperature is to master the basic law of the surrounding rock temperature field and the air temperature in the tunnel,especially to predict the air temperature under the condition of unexcavated tunnels,and the results can provide reference and guidance for the cooling scheme of actual engineering with high geothermal temperature.(1)Based on the basic steady-state heat transfer equation of surrounding rock and air,the third type of boundary conditions for heat exchange between air and inner wall is used to solve the temperature of surrounding rock and air simultaneously.Through detailed derivation,the analytical solution of the surrounding rock temperature and air temperature of the tunnel suitable for high geothermal temperature engineering is obtained.Applying the analysis solution to compare the data reported in the literature and the actual measured data,the results show that the overall temperature difference is within 1.0? and 0.5?,and the change trend of temperature is basically consistent.(2)The analysis solution of the surrounding rock temperature through the tunnel in this paper is applied to predict the surrounding rock temperature in both radial and axial directions,and the cooling effect of the insulation layer with different laying modes on the lining is quantitatively analyzed.The analysis shows that the increase in the thickness of the control heat circle and the heat flux density on the inner wall are respectively proportional to the decrease in air temperature in the tunnel by taking cooling measures.The temperature of the inner wall of the tunnel varies significantly within about 25 m at both ends of the entrance and exit.When the convective heat transfer coefficient is large,the effect of decreasing the thermal conductivity of the thermal insulation layer on reducing the temperature of the lining is weakened.When the thermal conductivity of the thermal insulation layer and the thickness of the material are used to define the thermal insulation layer's ability to lower the temperature of the lining,the influence of the convection heat transfer coefficient must be considered at the same time.(3)The air temperature at the location of the fan and near the working face under the condition of the construction tunnels with high geothermal temperature to be excavated with recirculation systems is predicted by applying the analysis solution of air temperature in the both through tunnel and construction tunnel.It is calculated that the air temperature at the location of the fan is 27.73? when the outside temperature achieves 27?.It is predicted that the highest air temperature of different excavation faces of the construction tunnel reaches 34.48?,35.67?,32.02? and 32.72? respectively,which all fail to meet the standard requirements of 28?.(4)Applying the analysis solution of air temperature in the construction tunnel,the maximum temperature within 100 m near the excavation surface at different wind velocities in the construction tunnel is calculated.According to the analysis,the maximum temperature near the excavation face decreases rapidly with the increase of wind velocity and then decreases slowly until it is stable.For example,in the case of tunnel construction with high geothermal temperature in this paper,from the perspective of ventilation and cooling effect,the wind speed should be controlled within the range of 0.5 m/s to 1.85 m/s as far as possible.(5)Combined with the analysis solution of air temperature in the through tunnel and construction tunnel,the maximum temperature near the working surface of the construction tunnel with high geothermal temperature under different outside air temperature and wind velocities conditions is predicted.Results show that for the high-temperature construction tunnels using double slopes with recirculation system,the air temperature near the working surface is affected by both the outside temperature and the wind velocity in the tunnel.Under the condition of a certain wind velocity,the critical value of the outside temperature that can determine whether the mechanical cooling equipment needs to be operated could be predicted.For example,in this paper,the wind velocity is taken to be 1.0 m/s while the tunnel is adopted by 3700 m-long double slopes with recirculation system,the critical temperature of the slopes entrance is 11? correspondingly.