Study On Fire Safety Of Urban Tunnel-subway-pipe Gallery Integrated Structure

The extension of urban development to underground space has become a new choice for sustainable development to solve many issues caused by the rapid development of China’s national economy and the continuous urbanization,such as the shortage of urban land resources,traffic congestion,repeated excavation of the road and so on.Meanwhile,adopting integrated structures by the co-construction of multiple types of tunnel such as urban tunnels,rail transit,and pipe gallery,has also become a new trend of intensive and three-dimensional development of underground space in major cities.For such an integrated tunnel structure,the fire in a tunnel might adversely influence other adjacent tunnels,and further threaten the safety of the whole structure.Therefore,the fire resistance and safety of the integrated tunnel structure under fire has become a critical issue that needs to be addressed urgently.In the present study,the Shangcheng Avenue in Yiwu is adopted as the relying engineering to investigate the distribution of temperature field,the degree of local high temperature damage,and the fire safety of the whole tunnel structure under fire by literature survey,indoor test,theoretical analysis,and numerical simulation.The main achievements are as follows:1.The fire scenario of the tunnel structure is designed,and the relevant thermal performance parameters of the concrete are selected.And,the temperature distribution law of concrete composite components under fire is proved by indoor test,the temperature field distribution and theoretical calculation formula of tunnel structure under different fire modes are also obtained by numerical simulation.2.The main control mechanism of high-temperature spalling of ordinary concrete in the tunnel under fire are explored by the literature research,theoretical analysis and numerical simulation,and the influence degree of different moisture content on the high-temperature spalling of ordinary concrete is clarified.By introducing the concept of critical spalling temperature of concrete,a numerical fire damage model of the tunnel lining is developed based on the existing non-linear transient thermo-mechanical coupled finite element model and cyclic spalling algorithms of the concrete,and the high-temperature spalling depth of tunnel structure under different fire modes is obtained by using this model.3.According to the literature research,the performance-based fire protection design method is introduced to better evaluate the fire resistance of the integrated tunnel structure.Additionally,the influence of fire scale,fire duration,fire location,and thickness of fireretardant coating on the fire safety of integrated tunnel structure is studied by the thermomechanical coupled finite element model.Finally,the recommended thickness of fire-resistant coating meeting the fire resistance standards of integrated tunnel structures is given.The above research results will not only be applicable to the integrated section of Shangcheng Avenue in Yiwu,the relying engineering of this paper,but also provide significant references for the fire resistance performance research of other similar integrated tunnel structures.