Research On Safety Risk Analysis And Control Of Foundation Pit Construction In Subway Station Based On Numerical Simulation

In the past two decades,the city scale of China has expanded rapidly,and the urbanization process has far exceeded the early planning which leads to the high concentration of urban core regional functions and population,traffic congestion has become a common phenomenon.The above-ground space in the city core area is limited,using the underground space to build rail transit has become an inevitable way to the development of urban transportation.Underground engineering construction itself is technically difficult and the engineering environment is complex,the interaction with existing high-rise buildings,bridges,underground engineering structures,etc.further increases the construction safety risks.Mastering the safety risk evolution rules of underground construction with dense buildings(structures),taking scientific and reasonable risk management measures to reduce the construction safety risks has a great significance to the healthy development of underground construction.This paper takes the deep foundation pit excavation project of Jie Daokou Station of Wuhan Metro Line 8 as the research object to study the safety risk and evolution of large ultra-deep subway station foundation pit under complex environment in the core area of the city.The main work and conclusions of this paper are as follows :(1)Combined with the subway construction safety risk theory and the actual situation of the project,systematically identified the safety risks existing in the construction of the station’s foundation pit,mainly including the foundation pit’s own structural risks,engineering and hydrogeological risks,surrounding environmental risks,construction and management risks;(2)FLAC numerical simulation software was used to build a simulation model which covered engineering geology,adjacent buildings(structures)(Fu Hua Building,viaduct),foundation pit supporting structure(enclosure pile,internal support).According to the model calculation results,this paper analyzed the deformation and destruction of surrounding rock during the excavation process,the deformation and internal force of the enclosing pile and internal support structure,and the deformation of adjacent buildings(structures)disturbed by the excavation of the foundation pit.Based on these analysis results,pointed out that the key stages of safety risk management are the 3rd,4th,and 5th stages of excavation.The key risk prevention and control positions include the bottom of the foundation pit,the side walls,the reserved core soil area,and the different settlement areas of Fu Hua Building,etc.Then put forward the corresponding safety protection points according to the actual situation.(3)The excavation sequence of the foundation pit,the diameter of the retaining piles and the unilateral load of the foundation pit have different influence on the stability and safety risk of the foundation pit.The results show that the asymmetric excavation of the foundation pit will increase the horizontal displacement of the retaining piles in the first excavation side and the displacement of the viaduct piles in the reserved soil area,which increases the construction safety risk.Expanding the diameter of the retaining piles will increase its ability to resist the deformation of surrounding rocks,but when the pile diameter increases to 1.6m,the effect of controlling deformation gradually decreases.When the load of Fu Hua Building increased,the horizontal displacement of the retaining pile increase in an opposite direction,and the uplift at the bottom of the foundation pit will also increase.(4)Based on the above safety risk analysis and conclusions of the influence factors of foundation pit stability research,this paper proposed some risk management and control countermeasures from the aspects of engineering geological risk management and control,deformation control of the foundation pit itself and surrounding buildings,construction management and emergency,etc.By using the numerical simulation method to analysis the safety risk evolution law of subway station open-cut construction under complex conditions,this paper has a great value for revealing the root cause of engineering risk and improving the scientificity of risk prevention and control technical measures and management countermeasures.