Deformation Monitoring And Numerical Simulation In Deep Foundation Pit Construction Of Subway Station

With the rapid development of my country’s rail transit engineering construction,deep foundation pit projects for subway stations are increasing.Excavation of deep foundation pits causes soil deformation.If the deformation is not controlled,instability accidents are very likely to occur.Studying the deformation law of deep foundation pit excavation is of great significance to deep foundation pit engineering.Based on the deep foundation pit of a metro station in Dalian,this paper carries out a numerical simulation analysis of the deep foundation pit excavation process.By changing the relevant parameters that affect the deformation of the foundation pit,the deformation law of the deep foundation pit under different conditions is studied.The comparison and analysis of the simulation data of excavation deformation and the actual monitoring data verifies the rationality of the built model,and hopes to provide technical support for the engineering design of this area in the future.The main research contents and results are as follows:(1)The deformation mechanism of deep foundation pit supporting structure system is analyzed.Through the analysis of the main deformation mechanism and calculation method in the process of deep foundation pit excavation,combined with the actual engineering based on this article,it is proposed that the foundation can be controlled by selecting the appropriate supporting structure system and real-time monitoring of the foundation pit excavation etc.(2)A simulation model for deep foundation pit excavation is established and the law of excavation deformation is analyzed.Firstly,build a simulation model of deep foundation pit excavation based on actual engineering.Then,the Moore Coulomb model was selected as the soil constitutive model through multi-factor comparison.Finally,the simulation data of the horizontal displacement of the enclosure structure,the surrounding ground settlement and the uplift of the bottom of the pit are obtained under various working conditions.(3)The influence of different parameters on the deformation of deep foundation pit excavation is studied.Firstly,the main factors that affect the deformation of the foundation pit are screened,and the deformation law and the dispersion coefficient of the foundation pit under different parameter conditions are calculated through numerical simulation.Then,the main application range of the model supporting structure system is analyzed.The calculation results show that the influence of soil elastic modulus,internal friction angle,cohesion and groundwater on the settlement of the surrounding soil is greater than the influence on the horizontal displacement of the retaining structure,the diameter of the retaining pile and the horizontal spacing of the supporting structure are opposite to it.The supporting structure system selected for this project is suitable for the range of 0.75 to 1.25 times of soil elastic modulus,0.75 to 1.5 times of internal friction angle and 0.75 to 1.5 times of cohesive force.The selection of the 1200 mm retaining pile diameter and the horizontal spacing of the internal supports of each layer not only meets the stability requirements of the foundation pit,but also reduces the construction cost and difficulty.The results calculated by the fluid-solid coupling model are closer to the actual situation,and the degree of deformation of the foundation pit without considering the groundwater exceeds 50%.(4)Monitoring data of deep foundation pit engineering of subway station is analyzed.Firstly,determine the actual construction monitoring plan and select deformation monitoring points.Then,sort out and analyze the deformation data under each working condition.It is found that the horizontal displacement deformation curve of the retaining structure is "bow" shape,and the maximum displacement value of ZQT11 pile is 12.80 mm,which occurs near the excavation depth of 11 m and does not reach the warning value of 30mm;The surface settlement curve of surrounding soil is parabolic,and the maximum settlement occurs at the settlement monitoring point about 5m away from the foundation pit.Finally,the comparative analysis of simulation and measured data verifies the rationality of the established simulation model,and provides certain technical support for future deep foundation pit excavation in this area.