Study Of Load-bearing Characteristics Of Super-long Large Diameter Bored Piles

Now, the economy of our country develops very rapid and violently, in order todeal with the complicated ground conditions, the pile obtained the more and morewidespread application. Especially as span Bridges, high-rise building loadincreasing, and coastal regions, the deep soft base area such as the widespreadadoption of bored piles, pile foundation to develop in the direction of large diameterand super-long pile. But for the load-bearing characteristics of super-long bored pilesis not distinct. By now, there is no method which agreed with practical situation. Thedesign method of large diameter pile in the applicable codes and standards cannotreflect the mechanism of load-bearing and deformation. In practice, the design ofsuper-long and large-diameter bored-piles based on codes which come from theconclusion of testing and researching short piles are not irrational, its makes the loadbearing of the piles have too large safety factor and differ from practice. Therefore,the study on the load-bearing properties of the large diameter pile is important tomeet the requirements of the theory and the reality.First of all, on the basis of a lot of reading related literature both at home andabroad, to summarize the advantages and disadvantages of bored piles. And summedup load-bearing characteristics of super-long pile and the influence factors of thebearing capacity of pile foundation, and summed up to determine several theoreticalmethods of large diameter single pile settlement and their applicability.Secondly, combining with the tianjin LNG storage tank engineering pile staticload test of pile foundation engineering site, sorting and analyzing test results, drawthe Q-s、s-�'t、s-�'Q curves, by means of FLAC3D numerical simulation software,reference to static load test results, adjust the contact parameters, complete model ofthe pile soil close to the scene of the project. Extract the axial force of pile, pile sideresistance, pile tip resistance and pile end settlement curve, to discuss theload-bearing characteristics and load transfer mechanism of super-long largediameter bored piles. Then from the Angle of pile diameter, pile length and pilemodulus of elasticity, to analyze its influence on pile foundation settlement. And bycontinuing to progressively load is applied to determine the ultimate bearing capacityof each test pile, and to determine its effective length.Then, using respectively the bridge pile foundation simplified method, the load transfer method, layered summation method and shear displacement method tocalculate the single pile top settlement, with reference to the static load test results, todiscuss and analyze the feasibility of the four methods of large diameter long pilesettlement calculation. Among them, the calculation results of the bridge pilefoundation simplified calculation method, layered summation method and the sheardisplacement method exists large errors, clearly incompatible with the measuredresults. But the load transfer method can well reflect the nonlinear between pile andsoil and the foundation soil layers, and the calculation results to converge with themeasured results, the error is small, and simple calculation. Therefore, using thismethod of large diameter bored piles in super-long pile top settlement is moreappropriate.