Study On The Deformation And Corner Effect Of Pit-in-Pit Deep Foundation Pit Adjacent To Buildings

With the advancement of urbanization process in China,the contradiction between urban people and land is becoming increasingly prominent,high-rise buildings and underground spaces are developing rapidly,and deep foundation pit projects of adjacent buildings are increasing.Due to the functional requirements of building,it is necessary to excavate small pit in deep foundation pit,that is,pit-in-pit deep foundation pits.And the corner effect of deep foundation pit can restrain the soil stress and displacement.Therefore,in the design process of deep foundation pit,the influence of surrounding buildings and pit-in-pit excavation,as well as the effect of corner effect,not only ensure the safety and stability of foundation pit engineering,but also reduce the project cost.Based on the background of foundation pit project of a building in Wuhan,this dissertation uses MIDAS GTS\NX finite element analysis software,using the control variable method,analyzes the influence of various factors of adjacent buildings on the deep foundation pit retaining structure;compares the influence with the pit-in-pit deep foundation pit of adjacent buildings,obtains the influence of pit-in-pit excavation on the effect of adjacent buildings;respectively studies the deformation of retaining structure near internal corner and external corner in corner effect,and the influence is obtained.The main contents and achievements are as follows:(1)The factors affect the deformation of the retaining structure of the deep foundation pit are summarized: this dissertation introduces in detail the action principle and influence of various factors on the deformation of retaining structure in the excavation of adjacent buildings and pit-in-pit excavation,and analyzes the phenomenon of corner effect and its causes.(2)Based on the background of foundation pit project of a building in Wuhan,a three-dimensional model of pit-in-pit deep foundation pit excavation under the influence of adjacent buildings is established.The feasibility of the model is determined by comparing the field measured data with the model calculation results.The horizontal displacement of retaining structure and surface settlement in each stage of foundation pit excavation are analyzed,and the change laws of them with the excavation depth are obtained.(3)This dissertation studies the influence of adjacent buildings on the deformation of deep foundation pit retaining structure: by changing the horizontal distance B between the building and the long side of the foundation pit,the soil stress p of the foundation soil of the building,and the form of the building foundation structure,the influence of various factors on the horizontal displacement of the retaining structure of the foundation pit are obtained.(4)In order to counter the influence of adjacent buildings on the deformation of retaining structure of pit-in-pit deep foundation pit,three different excavation models are established: deep foundation pit model(excavation to-19m),pit-in-pit deep foundation pit model(excavation to-19 m,pit-in-pit excavation to-26m)and foundation pit model(excavation to-26m),the influence of pit-in-pit excavation on the deformation of retaining structure of foundation pit is obtained;according to the calculation results of pit-in-pit deep foundation pit model,the influence of adjacent buildings on the deformation of retaining structure in the pit-in-pit deep foundation pit model is analyzed.(5)By analyzing the deformation of the foundation pit retaining structure without the adjacent buildings,the influence of the corner effect at the internal corner and external corner is obtained;introduced the function of adjacent buildings into the model,and apply the buildings near the internal corner and external corner,and change the distance D between the building and the corner,the influence of adjacent buildings near the external corner and the internal corner on the deformation of the retaining structure under the corner effect is obtained;the limit value of 5.0% displacement difference between no building and adjacent building foundation pit retaining structure is proposed to determine the influence range of adjacent buildings on the horizontal displacement of retaining structure,and the development law of influence range of buildings under the influence of corner effect is obtained.