| Under the implementation of the overall construction goals of"double carbon"and"pumped storage"in the 14th Five-Year Plan,the development of water conservancy and hydropower projects in China’s cold areas will usher in a new stage.The temperature change of hydraulic tunnel in cold area under ventilation condition is easy to cause freezing damage to the lining structure,which has adverse factors to the reliable operation of the project.It is necessary to optimize the lining structure of the tunnel to ensure the safety and stability of the hydraulic tunnel.Taking the hydraulic tunnel of Burenkou Hydropower Station in Xinjiang as the background,based on the relevant theories of heat transfer,thermodynamics and Mohr-Coulomb criterion,the convection-thermal coupling model and three-dimensional transient finite element numerical calculation model were established based on the relevant data of working conditions and other methods such as field monitoring,theoretical analysis and numerical simulation,and the temperature field of the lining structure at the entrance of the hydraulic tunnel was analyzed.Compared with the monitoring data,the model is proved to be reliable.Furthermore,the influence of temperature,stress and displacement of the lining structure of hydraulic tunnel in cold area on the above physical quantities under the coupled action of convection-thermal conductivity,as well as different laying positions and thicknesses of insulation layer were studied.Finally,the influence of frost heave on the temperature field,stress field,displacement field and plastic strain of the surrounding rock of the hydraulic tunnel is analyzed.The research results can provide theoretical reference for the optimization design of hydraulic tunnel lining structure in cold area.The main research work and conclusions are as follows:（1）Under the condition of ventilation,with the increase of radial and axial distance in the hydraulic tunnel,the influence of wind temperature and ventilation days（wind temperature）on the lining structure of the tunnel is gradually weakened.The temperature of the primary lining and secondary lining gradually increases,and the temperature of the secondary lining is lower than that of the primary lining,which shows the lag of radial heat conduction of the lining structure on the axial distance of the hydraulic tunnel.The temperature rise of primary lining and secondary lining decreased gradually,and the maximum temperature difference of primary lining and secondary lining was 8.400℃under different wind speed,which was basically consistent with the results of numerical analysis of temperature monitoring.（2）The maximum and minimum principal stresses of the primary and secondary lining are positively correlated with the temperature field above as the wind speed is constant.The maximum frost heave force was 1.535 MPa at the primary lining and 3.200 MPa at the secondary lining,both located at the arch waist.With the increase of wind speed,the stress values of the primary and secondary lining decreased gradually,and the reduction range decreased gradually,and the frost heave force increased gradually.The maximum frost heave force was located in the arch waist,and the primary lining was 1.281 MPa and the secondary lining was 3.866 MPa,both of which were the minimum principal stresses.The overall displacement of the primary and secondary lining is shrinkage in the transverse direction,and the upper and lower parts of the displacement are uplifted in the longitudinal direction.The horizontal contraction displacement of the primary lining is 0.3869 mm,and the upward uplift displacement is 1.380 mm caused by the frost heave.The frost heave of the secondary lining contracted horizontally by 0.3551 mm and lifted upward by 1.470mm.（3）Under the surface laying method,the frost heaving force on the lining decreases gradually with the increase of the thickness of the insulation layer.When the thickness reaches 0.06 m or above,the frost heaving force on the secondary lining changes into a certain compressive stress,and the temperature difference between the primary and secondary lining is the smallest.The transverse and longitudinal displacements of the primary and secondary lining no longer change and are close to the equilibrium value of in-situ stress,which is well verified with the analysis and prediction of the temperature field and stress field.The temperature of the secondary lining is negatively correlated with the thickness of the insulation layer.The frost heaving force increases gradually,and the compressive stress decreases gradually.The maximum principal stress changes from compressive stress to tensile stress.When the thickness is greater than 0.06 m,the maximum principal stress of primary lining is close to the maximum bearing strength.With the increase of insulation layer thickness,the transverse displacement difference of the primary and secondary lining increases by nearly 4 times,and the longitudinal displacement difference increases by more than 10 times.The surface laying method can effectively resist freezing damage,and the thickness of the insulation layer of the hydraulic tunnel is at least 0.06 m.（4）With the increase of ventilation time,the surrounding rock temperature decreases first and then increases.With the increase of wind speed,the surrounding rock temperature decreases gradually,and the temperature decreasing range decreases gradually.There is a negative correlation between the wind speed and the reduction of compressive stress of surrounding rock,and the maximum frost heave force of 0.7490MPa is located at the arch waist.Compared with the initial state,the surrounding rock as a whole is shrinkage in the horizontal direction and uplift in the vertical direction.The plastic strain of surrounding rock is up to 7.436×10-5 when the lining is frost heaved,which is more than 3 times of its initial value,and is positively correlated with wind speed and ventilation time. |
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