Influence Of Unsteady Temperature Field On The Stress Field In An Underground Circular Tunnel

After the tunnel is excavated,the stress field of surrounding rock is not only affected by the in situ stress,but also by the temperature change of the tunnel.Assuming that under the action of a heat(cold)source in the tunnel,the temperature at each point on the inner boundary of the surrounding rock is equal and has nothing to do with time,and always keep constant.If this temperature is not equal to the original temperature of the surrounding rock,heat conduction will occur inside the surrounding rock.This temperature change will produce temperature stress.If the temperature change is large,the temperature stress will also be large.At this time,the influence of temperature change on the stress field of the surrounding rock cannot be ignored.When designing tunnel lining support,the influence of temperature changes on the support design must also be considered.In this paper,the deep buried circular tunnel is simplified into an infinite domain problem,and the solution of temperature can be reduced to the solution of the unsteady temperature field under the first type of boundary conditions.The Laplace transform method is used to obtain the distribution law of the temperature field inside the surrounding rock of the tunnel,and then the temperature stress field caused by the temperature change is calculated by the analytical function.By superposing this stress field and the surrounding rock stress field caused by the original in-situ stress,the total stress field inside the surrounding rock can be obtained.The research focus of this paper are temperature field and temperature stress field and the main research contents are as follows:(1)For tunnels without lining support,the Laplace transform method is used to obtain the temperature field distribution in the tunnel surrounding rock.Based on this,through the stress boundary conditions at tunnel boundary and zero displacement boundary conditions at infinity,the solution equations expressed by analytical functions are listed.Then power series method of the complex function method is used to obtain the analytical function to be solved,so that the temperature stress field caused by the temperature change can be calculated.(2)For tunnels with lining support,can use the Laplace transform and the continuous temperature conditions of the contact surface to obtain the distribution law of the temperature field inside the tunnel lining and surrounding rock.On this basis,through the stress boundary condition of the inner boundary of the lining,the continuous condition of the interface between the lining and the surrounding rock and the zero displacement boundary condition at infinity,solution equations expressed by the boundary values of the analytical functions is established.The obtained analytical functions can be used to calculate the temperature stresses caused by temperature changes.This article compares the analytical solutions with the numerical solutions obtained by ANSYS,it is found that when the time is small,the results of the two agree well,which can verify that the process deduced in this article is correct.Through the calculation examples,the influence law of temperature on the stresses of lining and surrounding rock is discussed in two cases of temperature decrease and increase in the tunnel.The results show:(1)For the temperature stress of the tunnel with lining support,when the temperature in the tunnel is lower(higher)than the initial temperature of the lining and surrounding rock,and in the lining and surrounding rock near the tunnel:The radial temperature stress and the tangential temperature stress are both tensile(compressive)stresses.In addition,in the lining,the tangential temperature tensile(compressive)stress is much greater than the radial temperature tensile(compressive)stress.For the same moment,the radial temperature stress increases first and then decreases as the radius increases,while the tangential temperature stress decreases as the radius increases.The maximum tensile(compressive)stress value is obtained at the inner boundary of the lining.For tunnels without lining support,the change trend of temperature stress is basically the same as that with lining support.(2)For the total stress of the tunnel with lining support,the temperature change has a great influence on the total stress field of the tunnel.When the temperature in the tunnel is lower than the initial temperature of the lining and surrounding rock and the temperature difference is not very large,the compressive stress of the radial and tangential compressive stress in the lining will decrease,and the maximum tangential compressive stress will decrease more So that the lining is not easily damaged by compression.However,if the temperature is greatly reduced,tensile stress will appear in the lining,if the lining is made of concrete,the lining is easily damaged.When the temperature in the tunnel is higher than the initial temperature of the lining and surrounding rock,the radial and tangential compressive stresses in the tunnel lining will increase,especially the increase in the tangential compressive stress is greater,according to the strength criterion of the material,the temperature difference will make the lining more prone to compression failure.Tunnels without lining support are more prone to damage.