The Study On Anti-liquefaction Of Composite Foundation With The Open-hole Pipe Piles

In recent years,more and more attention has been paid to the problem of liquefaction of foundation under strong dynamic loads,so it is of practical significance to find a feasible method to deal with liquefiable foundation.Firstly,this paper introduces a kind of multipurpose perforated pipe pile invented by our research group,which has anti-liquefaction capability and can be used as engineering pile at the same time and carries out analysis and comparison of stress concentration and failure modes under static and dynamic loads.Then,through numerical simulation,the distribution of pore pressure field and settlement of natural foundation and composite foundation are explored.After that,the empirical formulas are adopted.Finally,characteristics of pore pressure dissipation of composite foundation with perforated pipe piles are explored by numerical simulation.The main research work is as follows:(1)The model of perforated pipe pile is established by numerical simulation,dynamic load and plastic damage model of concrete is applied to explore the change of stress concentration phenomenon and failure characteristics of perforated pipe pile under dynamic pressure,and compared with the corresponding characteristics under static pressure.It is found that the stress concentration in small holes is related to the change of dynamic load..The main damage reason of perforated pipe pile is caused by the interconnection of the plasticity region around the perforated pipe pile.(2)The distribution of pore pressure field of natural foundation and composite foundation with drainage body under seismic load is studied.It is found that pore pressure is related to the distance between pore pressure and dynamic load source..The drainage body has the ability to dissipate pore pressure,but the influence range is limited.In addition,the settlement of the two kinds of foundations under dynamic loads is qualitatively discussed.(3)Based on the assumption that the liquid flow in the hole of the perforated pipe pile satisfies the Poiseuille equation and the assumption that the equal strain is established,modificating pile modulus considering penetration of pile tip and top,the analytical solution of the vertical and radial combined pore pressure of the foundation under time-varying loads is derived in combination with the phenomenon of stress concentration in the composite foundation of the perforated pipe pile.Considering the accumulation of pore pressure under cyclic loading,the empirical model of pore pressure development is further used to improve the analytical solution.On the basis of this analytical solution,the development of pore pressure of perforated pipe pile,gravel pile,undrained pile and natural foundation is analyzed and compared,especially the factors affecting the dissipation of pore pressure of perforated pipe pile are analyzed.(4)The development of pore pressure of composite foundation with perforated pipe piles under dynamic loads is simulated numerically.The influence of pile-soil modulus ratio,load amplitude,load frequency,area ratio of opening and permeability coefficient of soil on the development of pore pressure is explored.In addition,the composite foundation with perforated pipe piles also has strong liquefaction resistance under multi-directional seismic loading.(5)Open-hole pile is a very effective measure to treat liquefiable foundation.On the one hand,it can dissipate the excess pore pressure generated during pile sinking and make the soil dense.On the other hand,when seismic load acts on the foundation,the excess pore pressure can also be discharged through drainage channel.That is,it can be used as a pretreatment means and act as a real-time drainage channel.