The Study Of Supporting Axial Force Of Effcet On The Safety Of Foundation Pit Crossing Engineering

In recent years, a lot of phenomena that projects under construction crossthrough existing projects are inevitably along with the construction of urban subway.Projects under construction in addition to keep its stability in construction process, butalso consider the safety of the existing project. In this paper, based on the expresswayconstruction engineering within satellite square node, the expressway excavationstability and deformation law of its own and main station structure are researchedthrough the theoretical analysis and field measurement data and numerical simulationmethods in view of the expressway across existing main station structure. The mainresearch contents and results are as follows：1.When active earth pressure behind the pile, passive earth pressure in thefoundation, additive axial force is simplified to concentration, the single pilehorizontal displacement in different additive axial force is calculated by using elastictheory method. As the additive axial force increases gradually, pile deformationpresents the "r" type deformation form then presents the "belly" form, eventuallypresents the "y" type deformation form.2.Expressway foundation pit was simulated according to the operation conditionof the asymmetrical excavation without additive axial force. Although expresswayfoundation pit has the effect of steel support, in the absence of additive under thecondition of axial force, expressway foundation pile horizontal displacement presentsthe form of upper large deformation lower small deformation towards the foundationpit. The midpoint of long side deformation is greater than the foundation of the shortedge points and the intersection point between the station structure and long side offoundation pit within the same foundation pit. Because of the difference of excavationsequence, pile horizontal displacements of foundation pit of first excavationis biggerthan the deformation of foundation pit after the excavation. Pile top horizontaldisplacement, pile top vertical displacement and ground surface settlement also had asimilar regularity, which shows that deformation of the retaining structure offoundation pit excavation is a host of other deformation.3.Pile horizontal displacement of main station structure general deviate from themain station structure, and is far less than expressway’s, which have experienced theprocess of toward a direction and springback. The deformation curve of horizontaldisplacement and vertical displacement of the wall shows obvious characteristics of rigidin each excavation stage.4.The measured axial force after set up support is far less than the designrequirements of pre axial force, which can’t effectively constrains upper deformationof pile in the early period, while cause pile upper large deformation lower smalldeformation. The first layer of steel support axial force increases gradually during theexcavation of foundation pit, finally maximum axial force is261kN, which just overthe design of200kN, and has a certain optimization space.5.Compared the measured data with the simulation results without additive axialasymmetric excavation, the scheme is optimized and simulated. The decrease of thepile top horizontal displacement deformation makes pile presents "big belly" forms,and pile maximum horizontal displacement reduced the6~8mm compared simulationresults with no additive axial asymmetric excavation. Other monitoring program ofthe simulation results are reduced, and ground surface settlement is within the scopeof control values which illustrate the application of the optimization of the scheme hasa certain value.