Behavior Characteristics Research On Tapered Pile In Soft Clay Foundation

Tapered pile was a good pile style due to its high bearing capacity per volume,and it originated from former USSR. Nowadays though the theory of tapered pile has been studied for almost 30 years,it is not universally used and aroused enough attention,which is due to the study on its bearing mechanism and characteristics have not deep understand as compared to the theory of uniform-section pile. In this thesis , the behavior characteristics of tapered pile in soft clay foundation are fully studied,and this research was supported by the National Natural Science Fund (50578169),and some achievements as follows:Pile foundation theory was introduced firstly,and current research and application situation about tapered pile at home and abroad are systemic summarized and analyzed. Then model tests on tapered pile and uniform-section pile are introduced. Based on the test results,a series of comparisons between tapered pile and uniform-section pile,for example, compaction effects of static piling, bearing behavior and load transfer law, etc.,are analyzed fully,and its primary factors of influencing behavior characteristics of tapered pile are also preliminarily studied. Additionally, mainly factors in influencing behavior characteristics of tapered pile were also studied.Based on two methods-cavity expansion theory integrated with load transfer method and load transfer method combining with increment method for nonlinear analysis,a nonlinear mechanical model and the interaction between tapered pile and pile-surrounding soil is established, respectively. A series of analytical formulae,for example,the relation between load and settlement,are obtained.Using the ADINA finite element software,model tests in-doors are simulated by three-dimensional numerical simulation. Based on numerical simulation result,bearing behaviors and load transfer laws are analyzed fully. Besides,the radial displacement of pile-surrounding soil and pile-tip soil are also studied.By a series of study,some conclusions are obtained as follows: 1 ) The earth's surface heave during static piling process of uniform-section pile. The place of maximal ground heave is 1~2 times of pile diameter apart from the pile axis,and the effective scale of ground heave is approximately 3~6 times of pile diameter;2)In the same geological condition,compacting effect caused by tapered pile is more obvious than that caused by uniform-section pile. The ground heave is more obvious as the diameter of pile-top enlarges,and maximal ground heave is 1~2 times of pile-top diameter apart from the pile axis,being 6 %~8 % of pile-top's diameter in heave value;3)Attenuation speed of ground heave surrounding tapered pile is quicker than that of uniform-section pile,when the distance from pile axial increases;4)In the same geological condition,the side friction of tapered pile is bigger than that of uniform-section pile;with increases of tapering angle, the side friction of pile increases and the bearing capacity per volume is also becoming higher;5)Under vertical load,both pile-surrounding soil and pile-tip soil of tapered pile cause radial displacement. The maximal radial displacement does not appear on the earth surface but at some depth under the surface,which would increases slightly as the taper angle increases.