Research On Temperature And Thermal Stress Field Of High Geothermal Tunnel Retaining Structure And Its Surrounding Rock

In recent years,the economic construction has developed rapidly,and a modern,high-quality national comprehensive three-dimensional transportation network is being established.The overall scale of railways and highways is also growing rapidly,and the construction of the tunnels involved has gradually entered the stage of deep-buried and grown-up.During the construction and operation of deep-buried long and large tunnels,they are often affected by high geothermal and high geostress.The issue of high geothermal and high geostress has attracted widespread attention from domestic and foreign scholars.In order to deal with the problem of "two-high",it is required to master the basic laws of temperature and thermal stress distribution of tunnel surroundrock and retaining structure,so as to provide reference for the design and construction of actual deep-buried long tunnel engineering.The convective heat transfer between the air in the tunnel and the inner wall of the tunnel has been considered in this paper.And based on the two-dimensional steady-state heat conduction equation of the surroundrock and retaining structure of the tunnel,and the analysis solution has been derived which is suitable for the temperature distribution of the two-layer surroundrock and the retaining structure of the tunneln;on this basis,simultaneous stress geometric equations,thermoelastic stress-strain constitutive equations,and equilibrium differential equations are derived to derive an analytical solution for the thermal stress distribution of the two-layer surroundrock and retaining structure of the tunnel with high geothermal.The temperature and stress distribution of surroundrock and retaining structure;the factors affecting the temperature and thermal stress of the surroundrock and retaining structure of the tunnel under high geothermal and high in-situ stress are analyzed,and the important factors affecting the stability of surroundrock and retaining structure are summarized.Taking the Dali-Ruili Railway Gaoligong Mountain Crossing Section Railway Tunnel Project as an engineering example,select the third type of heat transfer boundary conditions between the air in the tunnel and the inner wall of the tunnel,and apply the obtained analytical solution to calculate the two-layer surroundrock and support The temperature and thermal stress distribution of the protective structure,the following main conclusions are drawn:Ⅰ.The analytical solution of the temperature and thermal stress distribution of the tunnel supporting structure and surrounding rock has been derived.The calculation results of the analytical solution are compared with the data in the literature,and the results show that the error of the temperature field and thermal stress field is within 5%,and the change trend is consistent;Ⅱ.The axial temperature distribution results of the tunnel supporting structure and surrounding rock show that the axial temperature of the supporting structure and surrounding rock remains basically unchanged in the axial depth,which verifies the rationality of taking it as an assumption in general calculations;From the entrance of the tunnel,the axial temperature gradually increases inward from the value close to the outside air temperature,and tends to a certain stable value.The ratio of the length of the tunnel to the radius is about 9.0.Ⅲ.The radial temperature distribution results of the tunnel supporting structure and surrounding rock show that the temperature gradient in the supporting structure increases with the decrease of its thermal conductivity,and the temperature gradient in the surrounding rock is significantly smaller than the temperature gradient in the supporting structure;There is a relatively obvious temperature increase process at the interface between the supporting structure and the surrounding rock.Due to the differences in the thermal properties of the materials,the temperature transitions on both sides of the supporting structure.As the thermal conductivity of the supporting structure increases,both sides of the supporting structure The temperature difference decreases;Ⅳ.The calculation results of the tunnel support structure and the surrounding rock thermal stress field show that the analytical solution correctly describes the change law of the tunnel support structure and the radial thermal stress of the surrounding rock.“As the radius of the surrounding rock gradually increases,the The radial stress of the surrounding rock in and around it has changed significantly.In the deep part of the surrounding rock,the change of radial stress gradually slows down and approaches the original in-situ stress of the rock formation".The thermal stress of the tunnel support structure and the surrounding rock turns at the interface,and tensile stress appears near the side of the surrounding rock at the interface between the tunnel support structure and the surrounding rock.The radial thermal stress between the tunnel supporting structure and surrounding rock reaches a maximum value at about 3 times of the tunnel radius,then decreases and gradually approaches the original surrounding rock stress.The maximum stress here is 14.1% higher than when the temperature load is neglected.