Study On Mechanical Properties And Damage Laws Of Large Diameter Shield Tunnel Lining Under Fire Scenario

The lining of the most shield tunnel is a precast and assemblied reinforced concrete structure,which is a discontinuous hyper static structure,under the action of the fire,it will produce great thermal stress,and it's material properties is easy to deteriorate,so it's mechanical response is very complicated.In addition,due to a large number of joints,it is easy to generate stress concentration,which makes shield lining more easily damaged than integral lining under fire.Therefore,this paper takes the shield tunnel lining of Beijing Rail Underground Transit Line as an example,the mechanical properties and damage laws of the shield tunnel lining under fire are studied by means of protoype fire test and finite element numerical simulation.The main research works and achievements of this paper are as follows:(1)The tunnel fire scenario was analyzed from the heating process and the spatial temperature distribution of the fire,and the suitable heating curve was determined by comparison.According to the characteristics of the large diameter tunnel studied in this paper,two typical fire scenes were defined,which were non-uniform fire(the fire temperature is unevenly distributed on the tunnel cross section)and the uniform fire(the fire temperature is evenly distributed on the tunnel cross section).,setting and simulation methods of the fire scenes were proposed for different working conditions,which would provide a guidance for the fire test and numerical simulation analysis.(2)Based on the large diameter shield tunnel fire test platform built in this paper,the largest prototype fire test in China was carried out,and the mechanical properties and damage rules of lining under non-uniform fire condition were studied.First,the distributions of lining temperature and temperature gradient along with time and space during the fire were analyzed.Then,the physical damage forms(spalling,cracking and dehydration)and development laws of tunnel lining concrete under fire were analyzed,and the mechanism of burst of lining concrete under high temperature was explained from the point of view of energy.Finally,the deformation law of tunnel lining during the fire was analyzed,and the residual bearing capacity and the failure mode of the shield tunnel lining structure were expounded and analyzed through the ultimate failure test after the fire.(3)A three-dimensional finite element model for the thermal force coupling analysis of the shield tunnel lining was established,which took into account the cracking and crushing characteristics of the lining material under high temperature.By comparing with the results of the fire test,the temperature distribution law and the the deformation(radial and joint)law of the tunnel lining structure under the different fire conditions were studied.In addition,the change rules of force state(section stress,internal force and eccentricity)of tunnel lining under different fire conditions were studied emphatically,and the dangerous cross sections of tunnel lining corresponding to different scale fires were given.The above researches are helpful to correctly evaluate the working state of the shield tunnel lining under fire and the degree of damage after the fire.It can provide some basis and reference for tunnel fire safety design and post fire evaluation.