Study On Interaction Between Frozen Soil And Pile Foundation

With the development of economic science and technology,and deep development of western development.At the same time,pile foundation become the first choice for cold area buildings because of many good characteristics,adaptability to the frozen soil and convenient construction.How to solve the problem of frozen soil and pile interaction is the focus and difficult of cold area construction.In this regard,many scholars at home and abroad have used theoretical methods and experimental methods to study the interaction between frozen soil and pile interaction in two directions,and have come to very valuable conclusions.This paper first focuses on the theory and experimental study on the interaction of frozen soil and pile foundation.Then,the physical and mechanical properties of frozen soils are introduced,and the relevant mechanisms of frost heaving and thawing are analyzed.In this paper,the interaction of frozen soil and single pile is studied from two aspects: include model test and numerical calculation and analysis.(1)Based on the self-designed frozen soil-single pile model test device,the interaction of the frozen soil and single pile was carried out under the one-way freezing condition.The force and deformation behavior of the model single pile under unidirectional freezing conditions was studied.First of all,soil samples was conducted geotechnical testing,including soil moisture content,liquid plastic limit,permeability coefficient and other basic physical parameters.The test in the same soil water content,three different freezing temperatures:-5?,-10? and-15? as the main factors.The changes of the temperature field,the displacement at the top of the pile and the friction resistance of the pile in the frozen soil are studied.It is found that the temperature in the unidirectional freezing process is a direct factor,which is a ladder-like distribution in the frozen soil,the upper part of the soil have lower temperature then the lower part.So there is a temperature gradient.At the same time,the soil will undergo frost heave deformation,which led to the uplift of the pile foundation.The entire uplift process consists of three stages: the pile foundation without obvious uplift phase,the vertical displacement of the rapid growth stage and gradually stable stage,which accounted for the second phase of the largest.At the same time,the pile foundation is uplifted,the soil will apply friction to the pile foundation,the overall law is increased first or slightly reduced after,and the friction to maintain a balance in the all pile length.(2)On the basis of isotropic layered soil,then an initial frost heave strain is applied,and a simplified model of layered frozen soil is established.With the fictitious pile method,the axial strain at the point of the fictitious pile is perpendicular to the corresponding position of the extended half space as the coordination condition.The Fredholm integral equation of the second kind of the frozen soil and single pile interaction is established.Then,the fundamental solutions of RTM under isotropic saturated soil are introduced,and the integral equation is solved by numerical method.The axial force,tangential frost heaving force and pile displacement are obtained.Similarly,a melt-strain strain is applied to the model of the layered saturated soil to simulate the permafrost or seasonal frozen soil which upper thawed.Based on the integral equation model established above,the frost heave strain is replaced by the melting strain,and the second kind Fredholm integral equation of the single pile under the upper melting condition is established.The axial force,negative friction resistance and displacement of the pile are numerically calculated.It is found that the tangential frost heave force of the pile foundation is mainly distributed in the freezing depth and it has a positive correlation with the freezing depth and frost heave strain,it will lead to tensile deformation of the pile foundation.Similarly,there is a positive correlation between the negative friction and the depth of settlement and the thaw settlement strain.And at the same time,it will lead to compression deformation of the pile foundation.A numerical comparison can be found that the frost heave effect of frozen soil is more serious to the pile foundation than the effect of settlement.