Study On Setting Of Stress Release Holes For Pipe Piles Based On Excess Pore Water Pressure

Static pile can realize standardized production,good quality,high strength,short construction period,construction process has the advantages of low noise,no vibration,no impact force,and can be widely used in high-rise building foundation.However,as precast piles are extruded piles,the extruding effect generated in the process of pile sinking has great harm to the surrounding environment.Especially in pile group construction,the excess pore water pressure generated by pile sinking may have adverse effects on surrounding buildings and municipal pipelines,etc.,and the lateral stress generated by soil mass may also cause the pile body of adjacent piles to shift.With the continuous superposition of the excess pore water pressure,It may also lead to the increase of pile pressing force in subsequent pile sinking.Therefore,how to effectively reduce the excess pore water pressure generated by pile sinking and take corresponding construction measures are of great significance for site construction.This paper introduces the research status of the mechanism of static pressure pipe pile,analyzes the advantages and disadvantages of circular hole expansion method,strain path method and finite element method in calculating the generation and dissipation of excess pore water pressure,and puts forward the research method and technical route in this paper.Based on the analysis of the existing literature and the field measured data,the calculation formula and distribution rule of the initial excess pore water pressure in the process of pile driving in saturated soft soil are given,and the influencing factors are briefly analyzed,which provides a basis for the subsequent layout of stress release holes.The excess pore water pressure dissipates gradually with time after pile driving.According to Biot consolidation theory,the three-dimensional analytical solution of excess pore water pressure is obtained based on the dissipation of excess pore water pressure.This paper introduces the existing empirical formulas of pile driving resistance at home and abroad,analyzes the composition and influencing factors of the formulas,and puts forward the calculation formula of pile pressing force of static pile.Flac3 D finite element software was used to simulate the whole process of the generation and dissipation of excess pore water pressure.The calculation formula of pile pressing force based on excess pore water pressure was derived on the basis of the traditional formula,and the two formulas were compared.Aiming at the difficulty of pile group sinking,the method of setting stress release holes is adopted to reduce the pile pressing force of subsequent pile sinking.Combined with the actual plan,Flac3 D software is used to simulate the change of stress release holes under different combinations on the excess pore water pressure of subsequent pile sinking positions,and the influence of setting stress release holes with different hole depths and hole distances on the excess pore water pressure of subsequent pile sinking positions is analyzed.A reasonable combination of stress release holes can be obtained,and other construction measures can be combined with the setting of stress release holes.