Study On Deformation Mechanism Of Foundation Pit In Soil-rock Composite Formation

In order to solve the problem of land use shortage and traffic congestion,Qingdao began to develop rail transit.The construction of rail transit will inevitably require the excavation of some pits.Most of the foundation pits in urban areas are in closely connected buildings and municipal facilities.If improper control over precipitation and excavation,the surrounding buildings may sink or tilt,endangering the safe use of buildings,and even incalculable.Therefore,it is very important to study the surrounding ground and support system for excavation of foundation pits in Qingdao rail transit project.This paper relies on the foundation pit project of Zhangcun Station on the No.11line of Qingdao Rail Transit.Through on-site measurement and numerical simulation analysis,the ground settlement,displacement of the retaining structure,and the axial force of the anchor bolt during the excavation of the foundation pit are performed.The main research contents and achievements of the dissertation include:?1?Consult the relevant literatures to summarize the research status of the influence of excavation and precipitation on the surrounding surface stability.?2?Collect and sort the monitoring data of foundation pits.The main monitoring data includes deep horizontal displacement of retaining piles,surface settlement,groundwater level,axial force of anchors,and so on.?3?Using FLAC^3D finite difference software to establish a three-dimensional model,the deep horizontal displacement value,surface settlement value,anchor axial force of the retaining pile during the excavation of the foundation pit are calculated.?4?The deformation law of the retaining pile in the excavation process was analyzed.The deformation characteristics of the retaining pile is that the middle deformation value of the pile is larger,and the deformation value of the bottom and the bottom of the foundation pit is relatively small.As the excavation depth increases,the active earth pressure on the retaining pile will increase,and the passive earth pressure will decrease.The horizontal displacement of the retaining pile will increase as the excavation depth of the foundation pit increases.The maximum horizontal displacement during excavation of the pit often occurs at 1/2 to 2/3 of the excavation depth of the pit.?5?The analysis of the change curve of the surface settlement with excavation depth shows that when the foundation pit retaining structure has large rigidity and reliable construction quality,the surface settlement curve outside the foundation pit shows a“concave”groove distribution,and the maximum surface settlement value occurs at the distance from the foundation pit.At 10 meters,the maximum settlement is 15.42 mm.In the excavation of composite foundation deep foundation pit in Qingdao area,it is very important to ensure the construction quality of the envelope structure.?6?The simulation results of the surface settlement,deep horizontal displacement of the retaining pile and the axial force of the anchor bolt were compared with the actual monitoring values.The results show that the excavation of the foundation pit considering rainfall can more accurately reflect the deformation of the actual soil and the envelope structure.?7?Under consideration of precipitation conditions,the three-dimensional model was used to calculate and analyze the design parameters such as the design parameters of the retaining piles,the impact of construction methods,ground overload,and the influence of anchor dip angle on the deformation of the foundation pit.According to the law,the measures and methods for controlling the deformation of the foundation pit are proposed to guide the design and construction of the foundation pit project.