Study On Deformation Behavior And Its Impact Factors Of Deep Foundation Pit Supported By Pile Anchorage In Construction Cite Of Complicated Geological Conditions

The excavation of deep foundation pit, which is carried out in urban area withintensive buildings and complicated geological conditions, will surely have an impacton the surrounding buildings, underground pilelines and municipal facilities. In orderto reduce the influence of excavation on surrounding environment, the foundation pitmust be supported to control its deformation caused by the excavation. Especiallywhen the geological condition is complicated and the surrounding buildings allowlower deformation, to control the deformation of the foundation pit caused by theexcavation becomes more important. After doing sufficient investigation and study ofliterature, based on a deep foundation pit supporting by pile anchorage in Chongqingcity, combined with previous research, according to the control requirements ofdeformation caused by excavation, a systematic and profound study was done in thisthesis through theoretical analysis and by means of numerical simulation tool and fieldtest, which contains the deformation of the pile anchorage supporting system duringexcavation, the change of the surrounding soil, and the influence on the adjacent urbanroad and the existing pier. The main contents and results are as follows:①The pull-out test of tension dispersive anchorage cable was carried out in theconstruction site. The results show that the use of tension dispersive ahchorage cable inthis pit is suitable, the anchorage segment is able to provide requisite anchoragingforce when it is anchored in the silty clay of the construction site. The adhesivestrength was also obtained, which is required for numerical simulation analysis.②This thesis adopts the numerical analysis method, and the3D numericalanalysis model was created in this thesis. And then, the construction process issimulated according to the construction plan. The deformation of the supportingsystem and the surrounding stratum, caused by the excavation of the foundation pit,was made known. Result shows that the deformation of the north side of the pit, whichis close to the urban road, is a little greater. The maximum deformation appears nearthe boundary of the phase II and phase III, which is the most dangerous part of thefoundation pit. Results also show that the influence on the adjacent urban road and theexisiting pier, caused by the excavation of the foundation pit, is within the allowablevalue, the expected goal is achieved through present design of supporting system.③Through changing the parameters of supporing system, such as diameter of pile, angle of cable, pretension of cable, et al, this thesis presents the variation of theinfluence on the deformation of the foundation pit and the adjacent urban road, whichis caused by the change of the parameters of supporting system. Deformation of thefoundation pit and the supporting system under pile diameter of1.0m,1.2m,1.4m,1.6m and1.8m, cable angle of5o,15o,25o,35o and45o, cable pretension of50kN,150kN,250kN,350kN and450kN is obtained, and also the influence on the adjacenturban road.④The variation of influence on the deformation of foundation pit and supportingsystem was studied, which was caused by the change of thickness of the soil under thebottom of foundation pit. And the variation law and the influence on the adjacent urbanroad were obtained.