The Analysis Method Of Settlement For Gravel Pile Composite Ground Under Flexible Foundation

As the highway network in soft soil area is improving day by day,gravel pilecomposite ground under flexible embankment load has been widely used in manyfields.The traditional analysis theory of deformation for composite ground,as themechanical model be simplified in many aspects,sometimes was not accurate with theactual situation,for example,the assumption"the pile and soil have the same strain" isout of work in the condition of pile piercing the upper cushion layer,not consideringthe soil around the pile under load "have the different settlement",ignoring theobjective existing relative slipping on the pile-soil interface,and ignoring the gravelpile in radial has larger abscesses displacement in the position with lower confiningpressure,etc.Therefore,in view of the deformation problems of gravel pile compositeground under flexible embankment load,the reasonable analysis method shouldconsider the influence of the relative slipping between pile and soil,as well as theinfluence of the radial abscesses displacement in gravel piles.The existing analysismethod almost ignored these two characteristics.Firstly,the emphasis in this paper is aimed at the analysis in failure mode anddeformation mechanism of gravel pile composite ground under the flexible foundation,and setting up the analysis model as a units;electing or setting up the displacementfunction for soils around the pile;considering the characteristics of sliding betweenpiles and soils,the chosen vertical displacement function should be reflecting theinfluence of sliding between piles and soils,and the hypothesis that the relationbetween slip on the pile-soil interface and their friction satisfying the idealelastic-plastic model should be setted up;According to that the gravel pile abscessesdisplacement cannot be neglected,the soil’s radial displacement function isestablished;And then, we can get the forces between piles and soils with consideringboth vertical displacement function and radial displacement function of soil,finallyobtain the compression deformation of reinforcement area in compound groundaccording to the principle of load transfer method.Secondly,according to the gravel pile’s abscesses displacement in shallowposition is more obviously in engineering,people often would like to package thegravel pile with geogrid in the depth of2to3times of pile diameter,then,the reinforceform processes the reinforced-gravel-pile composite ground.Based on the bearingfailure mode and the mechanism analysis in this kind of composite ground,the paper has done a deep research in analysis method for the reinforcement area compressionof reinforced gravel pile composite ground under flexible foundation.According tothat the stiffness in the area where piles reinforced with geogrid and the area wherepiles were unreinforced are different,and the relationship between the slip on thepile-soil interface and their interface’s friction will change in different areas too,wewill divide the reinforcement area into three parts such as the reinforced-gravel-pilezone,the unreinforced-gravel-pile plastic zone and the unreinforced-gravel-pile elasticzone.In reinforced-gravel-pile zone and the unreinforced-gravel-pile plastic zone,theanalysis models were based on the the principle of load transfer method,and in theunreinforced-gravel-pile elastic zone,the analysis models were based on the soil’svertical and radial displacement function.Then,we can get the pile and soil’scompression computational method in each section, and ultimately get the newanalysis method for computing the settlement of reinforced-gravel-pile compositeground under the flexible foundation.Finally, we analyze two engineering examples with two methods that has beendeduced above.The result by this paper’s method is closer to the measured value.Forcomparing with the other methods,it shows that there is feasibility and superiority inthe method proposed of this paper.And the new methods could provide some modelsand the reference for the resembled construction,for design or something else.