| With the development of civil engineering construction,the urban land resource is increasingly nervous,building continuously build to the top or underground development.The construction of foundation pit excavation on the surrounding environment influence gradually aroused people’s concern, especially the nearby excavation of foundation pit of existing buildings.Excavation of foundation pit in a newly built building, the soil outside the excavation pit caused by the displacement of the adjacent pile foundation may cause additional displacement and bending moment. when reaching a certain degree, it will make the pile foundation damage, then affect the stability of the main building of the upper.The excavation will cause disturbance in the pit surface, and also increase the main body construction produce uneven settlement, then the upper structure wall crack, structure column buckling. People on how to predict and analyze the influence of excavation on adjacent buildings pile foundation and take the necessary protection measures to reduce the impact this hot topic to do a lot of research.CFG pile as its good economic performance, technical performance and environmental protection, can be used widely in our country. This article will first to introduce the CFG pile composite foundation and foundation pit engineering, mainly analyzes the current research status of foundation pit engineering. Second is to introduce relevant theory of foundation pit excavation.Then analyze from theoretical how the lateral soil and ground settlement caused by excavation will make effects on the surrounding environment. Read the related research methods, the commonly used are: the model based on Winkler foundation reaction method, the elastic theory method and finite element analysis method, etc. This article will use the finite element method, by using the finite element analysis software ABAQUS combined with the actual case to establish three dimensional numerical model for analysis of foundation pit excavation on adjacent buildings impact of CFG pile composite foundation. This article will introduce the modeling process, and where need to pay attention to each function module. Operating model then read the relevant data, using the form of a chart,etc,make comparing analysis, the conclusion is as follows:(1)By using the finite element analysis software ABAQUS to establish 5x5 model simplification of CFG pile composite foundation, two meter far from the center of the side away from the edge of the pile dig the eight meter deep underground garage foundation pit excavation,simulate the actual foundation pit construction process. According to the standard to calculate the final settlement of composite foundation deformation value for reference. Through the comparison and analysis can be concluded: Before excavation, read the foundation settlement value along the established path.We will find the value similarly. Due to the effect of wind load, lee to the side of the foundation numerical slightly larger,but all ciose to the theoretical value. After excavation, the subsidence value as the excavation depth increases,but growth is not big. A side close to the foundation pit degree of the affected than the other side. It also illustrates the excavation caused the foundation uneven settlement of adjacent buildings. The foundation settlement is controlled within the specification requirements before and after the excavation.(2)Excavation depth effect on the adjacent CFG pile mainly aimed at the influence of the stress and deformation performance. Choose five object for analysis: Pile lateral, settlement of pile, pile axial force, bending moment of pile and pile side resistance,to make a detailed research respectively. Selection of the foundation pit in the middle of the nearest pile of 15# pile,show the various values in the form of graphs respectively before the excavation,after four meter and eight meter excavation. The result show that, Pile lateral and settlement of pile body increase as the excavation depth increase. After excavation, the whole pile body tilt to the excavation, and the tilt rate increase as the excavation depth increase. The pile body tilt as well as increase the settlement of pile body. Following the excavation pile axial force increase, pile bending moment to the side of foundation pit excavation of variations is also increasing.But the pile side resistance is being reduced. This shows that when the pile and foundation pit spacing unchanged, the greater the excavation depth, the greater the stress and deformation of neighboring CFG pile composite foundation performance impact.(3)Research that center of the CFG pile spacing from foundation pit, also choose five object for analysis: Pile lateral, settlement of pile, pile axial force, bending moment of pile and pile side resistance. Selection of the foundation pit in the middle of a row of piles of 11#~15#,show the various values in the form of graphs respectively before the excavation,after four meter and eight meter excavation.The result show that, the same excavation depth, the 15# pile nearest the foundation pit is affected the most obvious. With the increase of the distance between center distance of pile foundation pit, pile lateral displacement and settlement of pile body and pile axial force decreases gradually, while the pile side resistance increases gradually, the extent of the pile bending moment to the side of foundation pit excavation change also gradually reduced. The deeper the foundation pit excavate, the more obvious of the impact. This shows that in the same excavation depth, the nearer spacing distance foundation pit, the more affect on the piles.Through the numerical simulation analysis of the actual project, we summarized the main factors that affect the CFG pile composite foundation excavation on adjacent buildings:the excavation depth and the center of pile spacing from foundation pit. To effectively reduce excavation causing adverse effects and provides practical significance in the future similar projects. |
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