Numerical Simulationanalysis Of Pile Foundation Deformation And Negative Friction

With the rapid development of engineering construction,pile foundation hadbeen used more and more widely. At present, the design and calculation of pilefoundation theory development was still far behind the engineering practice,especially for the compressive pile design calculation theory. The design of pilefoundation under the conditions of deep foundation pit excavation and the heap loadunder the design of pile foundation should pay great attention to the impact ofdeformation of the pile body and pile side friction.Combining with the engineering example,in this paper,by using FLAC3D finitedifference software,we simulate the axial force of pile, negative frictional resistanceand deformation rule under the conditions of deep foundation pit excavation and theheap load under the design of pile foundation.in the simulationthe above twocondition,we did a lot of simulation calculation to the value of pile soil contactsurface parameters and settings,we got the curves ofcontact surface parameters whichinfluence on simulation results.In the analysis of effects on foundation pit excavationto the bottom pile,we discussed the spacing between adjacent piles,postlength,diameter of pile and parameter value of soil calculations’ impact on pilefoundation in its excavation stage,then we obtained the variation of xial force, uppack rate,and shaft resistance in different parameters.On the other hand,when weanalysised the large-scale heaped load for the pile foundation,we took loadingsequence,loadingarea,load size,load on pile topsize,the diameter of the pile and thestiffness and strength of pile tip and pile shaft to pile foundation into consideration,sothat we got the axial force of pile body curve and the side resistance curve of pileunder different parameters,and we analysised of the changes in position of the neutralpoint and the pile tip penetration, in the end,we got the side resistance curve of pileby analysised unilateral load size, location, area and the influence of the loadingsequence on law of pile lateral extrusion,got the following main research results:(1) In parameters of contact surface of between pile and soil, lateral contactstiffness,the pile endcontact stiffness and the cohesion of pile side surface had greatinfluence on the axial force of pile and the negative skin friction of pile shaft,whilethe friction angle in the contact plane and the pile end contact surface cohesion didn’t play a so big role.(2)Pile foundation had certain restrictions to the bottom soil resilience.springback amount of pile top, the pile body tensile value,the maximum axialforcevalue and the springback of soil were Significantly increase with the increase of pilespacing.When the pile spacing is larger than8D, can did not consider the pile groupseffect;With the increase of pile length, bottom upheaval value and pile top rise weredecreased,But the pile body tensile capacity and the maximum axial force wereincreased;With the increase of pile diameter, elastic bottom soil, pile axial force andpile bottom up rate were be decreased, but the pile bending moment were increasedobviously.(3)In the given range of parameters,the bottom soil resilience is sensitive to thechange of sum.expansion line slope is sensitive to the change of pile topspringback.so the specific parameter sensitivity sequence was: expansion line slope ismore then poisson’s ratio,void ratio,initial consolidation line slope,consolidationcoefficient, cohesion and critical state parameters.combined with the third chapter ’sproject，analysis and comparison of the simulation results when soil parameters wereincreased by10%we knew that,Pile top rise would influence ranking orderparameters：degree of consolidation is more then poisson’s ratio,angle of internalfriction,void ratio,consolidation line slope,cohesion and critical state parameters。Soilresilience would influence ranking order parameters：poisson’s ratio is more thenangle of internal friction,degree of consolidation void ratio,consolidation lineslope,cohesion and critical state parameters。(4)Under the different loading sequence, the depth of pile neutraldifference,under the same load conditions, and worked in advance under anapplied,The axial force of pile, and the settlement of the pile top is the largest.As themost unfavorable condition,in the project it should be avoided. In engineering weshould first applied surcharge load,then the applied load on pile top,The settlementamount of piletop was relevant with the sequence of the pile of heaped load andthe loading of pile top.The final settlement of pile top was not simple superposited bythe load on pile top and settlement of pile top which was produced under The pile ofloading.The settlementcaused by negative skin frictionis composed of two parts,onepart was purely caused by negative skin frictionis, the other part was the subsidence caused by the pile segment shortening under the influence of negative skinfriction,when the load on pile top moved down to the location of neutral point.(5)The time when the pile had large area loading,if we did piles static loadingtest immediately,without considering the time effect of negative skin frictionresistance,test data obtained value would be bigger,this might overestimate thevertical ultimate bearing capacity of single pile,which should be paid more attentionin the detection of pile foundation.in addition also reflects the certain defectexistsnegative under friction of pile foundation detection.In piles static loadingtest,we were more error prone to detect the value of ultimate bearing capacity ofpile.As a result,when we did piles static loading test,we should be timely monitoringof pile top elevation,as the pile was made into.So in the field static load test,we alsoshould be based on the settlement of pile foundation as the initial static load testvalue.