| With the development of tunnel engineering in the direction of"deep,large,and long",high rock temperatures and heat damage occur frequently.The distribution of the temperature field in a high-rock temperature tunnel is one of the key factors in the design of tunnel engineering and the formulation of reasonable cooling measures.Therefore,it is important for engineering practice to master the distribution law of the tunnel temperature field.In this paper,a similar test method suitable for the study of the temperature field in a high-rock temperature tunnel is proposed by combining theoretical analysis,model testing,and numerical analysis.Based on the self-developed model test system of the temperature field of the tunnel with high rock temperature,the model test of the temperature field of the tunnel with high rock temperature was carried out,and the distribution characteristics and evolution law of the temperature field of the tunnel with high rock temperature were revealed.On the basis of the model test,the two-dimensional and three-dimensional unsteady conduction-convection coupling numerical models are established,respectively,and the reliability of the numerical models is verified by the model test results.Through numerical analysis,the distribution law of the tunnel temperature field under seasonal ventilation and different positions of ventilation pipes is further discussed.Based on the numerical model,the tunnel temperature field is analyzed by multiple factors,and the influence degree of each factor is ranked by grey relational analysis.The main research conclusions are as follows:(1)Based on the similarity theory,the similarity criterion of the temperature field in a high-rock temperature tunnel is deduced,and the similarity constant relation of the model test is obtained.The temperature field simulation test system for the high rock temperature tunnel was independently developed.The test system can simulate the initial temperature field of a high-rock temperature tunnel,different cooling measures during the construction period,ventilation cooling during the operation period,and other conditions.(2)The initial temperature field of a high rock temperature tunnel is studied experimentally,and the distribution law of the initial temperature field of a high rock temperature tunnel in a conductive geothermal field is revealed.Based on the model test,a two-dimensional finite difference equation for unsteady convective heat transfer is established,and the accuracy of the numerical model is verified by the test results.Taking Jiwoxiga Tunnel with its actual high rock temperature as an example,the initial temperature distribution is obtained by numerical analysis.The calculated results are basically consistent with the variation rules of the borehole data and the measured data after excavation,and the values are close to each other.(3)The experimental study on the temperature field of a high rock temperature tunnel during construction is carried out,and the temperature distribution law of the tunnel during construction is revealed under different cooling measures such as ventilation,placing ice cubes,and spraying.Before ventilation,the air temperature in the tunnel presents an uphill distribution from the entrance to the face of the palm,while after ventilation,the air temperature presents a high distribution in the middle and a low distribution at both ends.The relationship between dimensionless temperature and dimensionless time in the surrounding rock during construction is a logistic function(Θ=A+B/(1+CFo~D)).With the increase in wind speed and the decrease in wind temperature,the rate of decrease in temperature increases,and the decrease in surrounding rock temperature caused by the decrease in wind temperature is more obvious than that caused by the increase in wind speed.The cooling range and magnitude caused by the placement of ice cubes are small.The spray can quickly reduce the ambient temperature of the palm surface,but when the temperature drops by 42.27%,the humidity increases nearly twice as much.Under the comprehensive cooling measures of ventilation,spraying,and placing ice cubes,the air temperature measurement points all dropped below 28°C,and the relative humidity remained at about 60%.(4)The experimental study on the temperature field of the tunnel with high rock temperatures during the operating period is carried out,and the temperature distribution of the tunnel under different wind speeds and temperature conditions is revealed.After ventilation,the temperature in the cave increases linearly from the entrance section.The radius of the heat-regulating ring is different in different parts of the tunnel.The radius of the heat-regulating ring is the largest in the vault area,followed by the side wall area,and the minimum in the invert area.The influence of wind temperature on the heat-regulating ring of surrounding rock is less than that of wind speed.The relation between dimensionless temperature and dimensionless radius of surrounding rock in the tunnel arch area is a cubic polynomial,and the relation between side wall area and invert area is an exponential function.Based on the model test,a three-dimensional unsteady conduction-convection coupling numerical model is established,and the test results verify the reliability of the numerical model.Taking the actual tunnel as an example,the temperature distribution rule under seasonal ventilation conditions is obtained by numerical analysis.Under the condition of seasonal ventilation,the temperature near the measuring point outside the lining changes periodically with time.Within 1 year of ventilation,the rate of temperature decline is fast,and after 5 years,the trend tends to be stable,in which the radial depth range of 5 m has the most significant influence.(5)Through numerical analysis,the influence of different distances between the ventilation duct and the face on the air temperature distribution in the tunnel is discussed,and gray correlation analysis is carried out on the influence factors of the temperature in the tunnel surrounding rock during the operation period.Through calculation,it is found that when the distance between the ventilation duct and the palm surface is equal to 24 m,the cooling effect of the palm surface area is better.The air temperature at the bottom of the air duct is generally high.It is recommended to place ice or spray at the bottom of the air duct to reduce the temperature.Through grey relational analysis,it is concluded that the main factor affecting the surrounding rock temperature is the thermal conductivity of the lining;wind speed is the second factor;and the thermal conductivity of the surrounding rock is the third factor. |
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