Research On Soil Foundation Consolidation Of Single Permeable Pipe Pile With Considering Disturbance Effect

During the installation process of precast pipe piles in soft soil foundation(with high moisture content,high compressibility and low permeability),the installation often cause soil squeezing and corresponding excess pore water pressure.The excess pore water pressure in soft soil foundation dissipates slowly,which leads to a reduction in the rate of soil consolidation and affects the performance of pile capacity and the construction progress of sinking piles,ultimately cause economic loss.Therefore,how to accelerate the dissipation of excess pore water pressure is a problem that can’t be ignored.The permeable pipe pile technology proposed by research team can solve the former problem well.In addition,the disturbance effect caused by the pile installation has a reduction on the dissipation rate of the excess pore water pressure.Therefore,it is necessary to conduct research on the soil consolidation of permeable pipe pile that considers the disturbance effect.Based on the existing research method of permeable pipe pile consolidation characteristic,soil consolidation around a permeable pipe pile with considering disturbance effect is investigated in the current study through model test,theory analysis and numerical calculation.The main research and conclusion are as follow:(1)The model test of the permeable pipe pile is carried out,which researches the influence of disturbance effect on soil consolidation of permeable pipe pile after the pile installation.The dissipation of excess pore water pressure with time and location,the superposition displacement of soil surface are analyzed.The results show that the excess pore water pressure increases with the depth of soil and decreases with the radial distance.Under the same conditions,the disturbance effect of the permeable pipe pile is smaller than that of the normal pile.The disturbance range has the characteristic of increasing with the depth of the sinking pile.Compared with normal pipe pile,the performance of permeable pipe pile in reducing the excess pore water pressure is obvious.The displacement of soil surface near the pile side is the largest,which decreases with the radial distance.When the radial distance increases,the vertical displacement gradually changes from settlement to heave.It demonstrates the mechanism of the disturbance effect influence on the soil consolidation around the permeable pipe pile and lays a scientific foundation for the construction technical specification for permeable pipe piles.(2)The consolidation theory of permeable pile foundation with considering disturbance effect and interface parameter is derived.The influence of parameters(i.e.,radial distance r,vertical depth z,permeability coefficient ratio kh/kd,radius ratio of disturbance rd/rw and the interface parameter μ)on the excess pore water pressure are analyzed.The theoretical solution is combined with the results of the model test for comparative analysis.The results show that without considering disturbance effect,the dissipation rate of the excess pore water pressure would be overestimated,and thus capacity of pile would be also overestimated.The dissipation rate of the excess pore water increases with the permeability coefficient ratio and the interface parameter of pile-soil interface.Therefore,it’s a reasonable and effective theoretical method for studying about the working characteristics of permeable pipe piles.(3)The numerical simulation of the soil consolidation around permeable pipe pile with considering disturbance effect and variation of radial permeability coefficient are carried out.The excess pore water pressure around a permeable pipe pile under different opening parameters(i.e.,the opening ratio η,opening pattern,opening number of single-layer n)are analyzed.The results show that the dissipation rate of excess pore water pressure around permeable pipe increases with opening rate.When the rest opening parameters remain the same,the dissipation rate of the excess pore water pressure increases with the opening number of single-layer opening decreases.In the same pattern of opening,the disturbance effect has a significant influence on the dissipation rate of the excess pore water pressure under different opening rate and number of single-layer.For different patterns of variation of radial permeability coefficient,the dissipation rate of the excess pore water pressure is the fastest when the variation of radial permeability coefficient is nonlinear in the whole effecting area.For patterns 1～4(a constant changed permeability coefficient within the disturbed soil zone,a linearly changed permeability coefficient within the disturbed soil zone,a nonlinearly changed permeability coefficient within the disturbed soil zone and a linearly changed permeability coefficient within the whole influence zone),the average excess pore water pressure dissipation rate near the pile side decreases gradually with the increase of the disturbance radius and permeability of disturbance soil.The variations of disturbance radius and the permeability of disturbance soil are not important factor to the average excess pore water pressure dissipation near the pile side under pattern 5(a nonlinearly changed permeability coefficient within the whole influence zone).It provides a scientific basis for the popularization and application of permeable pipe pile.