Study On The Working Characteristics Of PHC Pipe Pile Internal Bracing In Deep Soft Soil Area

In recent years,prestressed high strength concrete pipe pile(PHC pipe pile for short)is more and more used as engineering pile;At the same time,because of its reliable quality,fast construction speed,good environmental protection and other advantages,PHC is also increasingly used as the foundation pit supporting structure.Compared with large-size cast-in-place piles,PHC piles are usually smaller in section size and have poor flexural and shear resistance.Therefore,PHC piles are mainly used in deep soft soil foundation pit supporting engineering with small depth at present,and are often used in combination with internal support.Strengthening the research on the working characteristics of PHC pipe pile internal bracing supporting structure is conducive to revealing the mechanism of PHC pipe pile internal bracing supporting structure system,thus providing theoretical guidance for the popularization and application of PHC pipe pile internal bracing supporting structure.In this paper,taking a deep soft guangdong foshan Tu Guan pile supporting foundation pit support engineering as a case,using the method of finite element numerical simulation and actual monitoring analysis method,the study of the supporting system without considering groundwater pipe pile brace support working traits and to optimize the design of the support structure,considering the groundwater seepage in support work character of two kinds of situation.The results show that:(1)The results show that the settlement of the road around the foundation pit is U-shaped.The horizontal displacement of the deep layer of soil presents a parabolic distribution,and the maximum value is always near the excavation face.In deep soft soil area,the pipe pile and pile under the condition of same combined bolting,pipe pile and pile deformation trend is the same,but the deformation of piles as a whole are smaller than that of PHC pipe pile,both in a safe range,so the PHC pipe pile instead of filling pile in the deep soft soil area is safe,for later in the design of foundation pit in the region provide a more economic and environmental protection pile type selection;The position of internal support has two inflection points for the variation trend of pipe pile deformation and surrounding soil settlement.At the first inflection point,the displacement of pile top and the maximum displacement of pile body increase first and then decrease.At the second inflection point,the displacement of pile top,the maximum displacement of pile body and the trend of road settlement decrease first and then increase.When the inner support moves down within a certain range,it will significantly reduce the deformation of pipe pile and road settlement,and the effect will be reduced if the inner support moves down within a certain range.Increasing the stiffness of the internal support can significantly reduce the pile displacement and surrounding road settlement in a certain range,but the effect will be significantly reduced beyond this range.(2)The distribution of pore water pressure and the size and direction of seepage velocity generated by the foundation pit are studied with the consideration of groundwater.In the process of the rise of groundwater level,the displacement of pile head and pile body increases continuously,and the maximum increase range is from-3.0m to-1.5m in the groundwater.In the process of groundwater level rising,the settlement of surrounding roads is decreasing.The research results of this paper can be used as a reference for the design of pipe pile internal bracing system in deep soft soil area.