Research On Bearing Characteristic Of Composite Foundation With Lateral Restriction And Reinforced By Geocell And Rammed Tapered Cement-soil Column

With the rapid development of China’s highway construction,all kinds of soft soil problems encountered increasingly prominent,a variety of ground treatment technologies are emerging,including for the development of composite foundation technology is more prominent.Based on the research and analysis of rammed tapered cement-soil column composite foundation,composite foundation with reinforced cushion and the lateral restraint technology,our team creatively put forward a fresh technology,composite foundation with bidirectionally reinforced by geocell and rammed tapered cement-soil column in lateral restraint,to reinforce highway soft foundation.This paper adopt a combination method,which include laboratory soil test,laboratory model test,FLAC3 D numerical simulation and summary.And systematically analyse the conditions that the settlement characteristics of composite foundation with bidirectionally reinforced by geocell and rammed tapered cement-soil column in lateral restraint,lateral displacement rule of constraint structure,the evolution rule of column-soil stress ratio,the distribution law of pile axial force and some others working characteristics under the vertical load.The main research work include follows,First,in view of the reinforced effect of geocell reinforced cushion,this paper take a method that combine laboratory model test,FLAC3 D numerical simulation together and analyse the working characteristics of pure cushion and reinforced cushion on natural ground.The conclusion indicates that gravel cushion shows better regulating capacity than coarse sand cushion.Lay of geocell in gravel cushion can effectively improve the mechanical properties of cushion,enhance the integrality of cushion and makes cushion work as a plate structure with large rigidity,which can be better homogenize the upper load to ground surface so as to reduce the harm of partial stress concentration in soft soil foundation.Second,based on the similarity theory,6 groups model designed in composite foundation with bidirectionally reinforced in lateral restraint and respectively carry out the composite foundation load tests,carry out the contrast analysis of the lateral restraint,geocell reinforced cushion,wedge angle and some other factors infecting the bearing behavior of rammed tapered cement-soil column composite foundation.The conclusion indicates that: 1)The pile-soil load contribution regularity of rammed tapered cement-soil column composite foundation has some certain similarities.However,the settlement of edge column,central column and angle column shows obviously difference.When on the same conditions,the central column gets the largest settlement,then the edge column and the last is angle column;2)Lateral restraint structure shows resist and hijack action to the soft soil in reinforced area,which can effectively reduce the settlement of composite foundation and strengthen the column-soil interaction as composite foundation.;3)Composite foundation with bidirectionally reinforced by geocell and rammed tapered cement-soil column can effectively improve the bearing capacity of foundation and decrease the uneven settlement;4)Under the same loads,the settlement of rammed tapered cement-soil column is obviously smaller than rammed soil-cement cylindrical columns composite foundation.Last,based on the large scale model test results and the FLAC3 D used for three dimensional numerical analysis,the influence parameters including cushion,lateral restraint,wedge angle,column space and several others are comprehensively discussed for the load bearing characteristics of rammed cement-soil column composite foundation.The conclusion indicates that: 1)The bearing characteristics of composite foundation is much related with parameters like column spacing,geocell reinforced cushion,wedge angle and lateral restraint,and most important factor is column spacing;2)The increased extent increases with the increase of wedge angle while in a small range(the wedge angle is ranged about 0.7°~1.7°);3)While the column space is less than 4DZ(DZ means the average diameter of a total taper column),rammed tapered cementsoil column and restrained column show intense hijack action to soil between columns,and column-soil stress ratio will increased with the decrease of column space,and more eventually reaches a certain value.In the condition of lateral restraint,the most optimum column space of geocell and rammed tapered cement-soil column composite foundation is about 2~3D_Z.