Model Tests On Stability Of Existing Building Pile Foundation Under The Condition Of Deep Excavation

With the deepening of the urbanization development in our country, subsurface development and utilization has aroused people’s great attention. Especially with the increases of private cars defects of use function are getting more and more obvious, of which the lacking of parking space in existing buildings. When the existing buildings construct additional underground space we need to use the original or addition new pile foundation to support the upper buildings, in order to excavate the soil beneath the buildings. Compared with the original pile foundations, the naked pile’s characteristics will change after the soil excavation, especially the plies bucking stability reducing. Therefore, the analysis of the existing buildings plies bucking stability reducing under excavation is necessary.This article of pile to soil under the condition of excavation unloading of steel pipe pile bucking stability were studied,by model experiment.(1)Obtained pile body stress and load variation under different excavation depth of pile foundation.(2)From the contrast testing results under various pile or soil materials slenderness ratio and embed proportion of pile shaft and the constraint conditions at the pile top or tip.The buckling failure mechanism of pile shaft are obtained in depth,which may be used to guide the study of pile group buckling.(3)Through pile buckling ultimate bearing capacity of the pile foundation of the further deduced under the condition of excavation stability coefficient and the coefficient of length.As can be seen from the results of the analysis,(1)Pile top load is far less than the buckling limit load, steel pipe pile body strain is linear increase with the increase of load,And when the pile top load close to the buckling limit load,Near the pile-soil interface of the pile body strain mutation.(2)The position of the pile buckling failure happens near the pile soil interface.(3) The ultimate bearing capacity of steel pipe pile buckling significantly decreased with the increase of excavation depth.(4) At the same time of pile soil excavation depth.Upper end articulated, bottom fixed edge coefficient of ultimate bearing capacity and stability of the steel pipe piles were significantly greater than both ends hinged steel pipe piles,The calculated length coefficient is less than two end hinged steel pipe piles.(5)The pile soil excavation ratio greater than 0.5,Radius of gyration greater stability coefficient of steel pipe pile is larger.Pile soil excavation ratio is less than 0.5, the radius of gyration greater stability coefficient of steel pipe pile is small.(6)Through setting levels respectively in the pile top and pile support,can obviously improve the pile ultimate bearing capacity and stability coefficient of test results for the pile foundation to support existing buildings provide theoretical support for the development of underground space.