The Finite Element Analysis Of The Mechanical Properties Of CFG Pile Composite Foundation With Small Diameter

With the development of civil engineering construction, the foundation of high-risebuildings along with the increasing of the height of the upper structure, have importantresearch significance. The research of small diameter of CFG pile composite foundation isone of the important content of a number of researches about foundation. First using thetheory of CFG pile composite foundation design method and the calculation data ofpractical engineering, design and verify the rationality of the design of practicalengineering foundation.When this paper introduces the existing research theory, it illustrates the settings ofthe cushion, as well as to define the replacement ratio of composite foundation, the stressratio between pile and soil, and the load share ratio between pile and soil. Secondly, in themechanics performance of soil, it mainly introduces the method for calculating the ultimatebearing capacity of foundation, used the Rankine theory formula; In the Settlementcalculation method of soil, it mainly introduces the initial settlement calculation formula.Pile mechanical performance include: the calculation method about the ultimate shaftresistance of a single pile and the calculation method about the ultimate tip resistance inpile foundation, provides the basis for the following analysis about the ultimate bearingcapacity of the pile in pile group composite foundation. It also introduces the failure modeof the pile group and the different methods about determining the limit load of two stressof pile.On the basis of predecessors’ research about the CFG pile composite foundation,setting up the finite element numerical model, the results show that:(1) through theanalysis of the stress ratio between pile and soil and the pile-soil deformation data underdifferent thickness of cushion, draw the conclusion: when thickness of cushion is250mm,the effect about adjustment the load share ratio between pile and soil is best. Cushion is outof step with its thickness, exist reasonable thickness of cushion in the actual design.(2) byanalyzing the data about the deformation of piles and soil, draw the conclusion: thesettlement of numerical calculation value on the bottom of foundation is closed to the valueof settlement according to the rules, which shows the rationality of the numericalsimulation of the model. The ability about pile bearing the upper load is strong in themiddle of foundation. The ability about pile bearing the upper load is bigger in the sidethen in the middle.(3) by analyzing the formation process of pile body compression bulgearea changing with load time, it knows that the CFG pile by pile side friction effect bearing the upper load. The function of the shaft resistance is obvious under the range of thecompression bulge area, the role is very small when exceed the range.(4) the numericalanalysis results of the edge load action show that: the edge load action can improve thebearing capacity of composite foundation. Settlement value of the edge load state isrelatively large under the same load. By edge load compressing the soil outside thefoundation, the settlement value of pile is bigger than the condition about no edge load.The edge load action can improve the bearing capacity of soil between piles, the settlementcompared with the boundless load conditions which haven’t changed much.(5) within therange of the bearing capacity characteristic value of soil between piles and under thecontrol of composite foundation settlement, composite foundation bearing capacity ofextreme value is about1200kPa, which shows that the actual project can be optimizeddesign on the basis of the original design.(6) It put forward two kinds of optimizationdesign, reducing the pile length and increasing pile spacing. The numerical analysis resultsshow that, the increasing pile spacing method is more safe and reliable under600kPaupper load. The settlement numerical value of reducing pile length method is bigger thanthe settlement value of increasing pile spacing. Under the condition of requiring smallersettlement value, the increasing of pile spacing method is more reasonable.Through finite element simulation of small diameter of CFG pile compositefoundation mechanical properties under bearing capacity limit state, optimization design isput forward. In the part of the numerical analysis of optimization design, this paperconfirms that the increasing of pile spacing method is feasible. In order to improve theeconomic benefits of engineering, it has important practical significance.