Researchon Thermal-mechanical Coupling Mechanism And Stability Analysis Of Immersed Tube Tunnel Concrete Subjected To Fire Accident

Since the beginning of the 21 st century,China’s national economy has continued to develop,and exchanges in various regions of the world have become more and more frequent.Therefore,many famous underwater immersed tunnels have been built one after another.Shenzhen-zhongshan immersed tube tunnel adopts a rectangular frame structure with two holes and a corridor.The standard pipe section has a cross-section width of46 m,a maximum cross-section width of 55.47 m,a maximum tube bottom burial depth of 38 m,and a pipe backfill covered with backfill.Due to its narrow and long structure,small space,and poor ventilation conditions,the consequences of fire in the tunnel will be very serious.In addition to causing damage to people,it will also cause cracking of concrete and deterioration of structural performance due to high temperature.As a result,the bearing capacity of the structure will also be greatly reduced,resulting in damage to the structure.Considering the above characteristics,it is particularly important to carry out the research of immersed tube tunnel under temperature-stress coupling.Relying on Shenzhen-zhongshan immersed tube tunnel project,this paper studies the thermodynamic properties of the concrete structure of the immersed tunnel,and establishes the temperature-stress coupling model of the immersed tube tunnel.The specific contents are as follows:(1)The three-dimensional thermal expansion strain and three-dimensional thermal expansion stress of concrete structure at 600℃ are obtained by carrying out the thermal expansion test of concrete under three-dimensional stress state,and the law of thermal expansion coefficient of concrete structure changing with temperature under three-dimensional stress state is obtained.(2)By carrying out triaxial tests of concrete under high temperature,the laws of the mechanical properties of concrete changing with temperature are analyzed,and the thermal parameters of materials changing with temperature are determined to prepare for the calculation of the immersed tube tunnel model.(3)Based on the theory of thermoelasticity,the finite element analysis software COMSOL is used to establish the temperature-stress coupling model of the immersed tube tunnel.According to different fire conditions,the corresponding temperature load is applied to the structure boundary;according to the geological environment of the immersed tube tunnel,corresponding stress load is applied to the exterior of the structure.The internal stress and total displacement of the structure using thermal expansion coefficient under the three-dimensional stress condition and free-stress condition were compared.