Research On Risk Assessment And Control Technology Of Adjacent Structures By Deep Foundation Pit Excavation

With the rapid development of urban construction,urban land is increasingly tense.In order to improve the land utilization,there are a large number of high-rise buildings and underground projects,so there are more and more deep foundation pit projects.Most of the deep foundation pit projects are located in the downtown area of the city,the surrounding environment is complex,and there are many buildings close to the foundation pit,which leads to the difficulty of deep foundation pit construction is also increasing.During the excavation of deep foundation pit,it is necessary not only to ensure the safety of its own structure,but also to ensure that the impact on adjacent structures is within the safe range.Therefore,it is of great practical significance to comprehensively analyze the risk factors of deep foundation pit engineering system and take scientific and reasonable control measures to reduce the deformation of its own structure and adjacent structures.Based on a deep foundation pit project in Chongqing,the main research contents are as follows:(1)Combined with the actual project,this paper summarizes the common risk sources in the construction process of the deep foundation pit project adjacent to the existing structures,and on this basis,constructs the fault tree model based on Bayesian network,carries on the risk assessment of the deep foundation pit project,analyzes and obtains the accident probability of the deep foundation pit project adjacent to the existing structures and the importance of each risk source,And take control measures to the important risk sources to reduce the probability of foundation pit accidents.The application of fault tree analysis based on Bayesian network in practical engineering is studied.(2)By using MIDAS GTS / NX finite element software,a three-dimensional model including foundation pit engineering,adjacent structures and surrounding soil is established.Three different layered excavation sequences are simulated.The deformation laws of foundation pit supporting structure,surrounding ground settlement and adjacent structures are obtained,and the deformation characteristics of adjacent structures under different construction conditions are summarized.(3)The detailed monitoring scheme is prepared to monitor the top horizontal displacement of the supporting structure,the deep horizontal displacement of the supporting structure,the settlement of the surrounding surface and the settlement of the adjacent structures in real time during the construction of the deep foundation pit.The deformation law of each monitoring object is obtained by analyzing the monitoring results.By comparing the monitoring data with the numerical simulation results,the reliability of the numerical simulation results is verified.(4)Based on numerical simulation,the influence of diaphragm wall thickness and ground overload on the deformation of adjacent structures is studied.By changing the parameters of diaphragm wall and ground overload,the influence law of various factors on adjacent structures is found,and then the measures to control the deformation of foundation pit and reduce the settlement of adjacent structures are found.According to the analysis results,the measures to control the deformation of adjacent structures are proposed from three aspects of source control,path partition and object protection.