| The pile-soil interaction in negative skin friction (NSF) pile is very complicated. Although researches on NSF of pile lasted about seventy years, many important aspects on NSF in piles should be studied. Based on former researches on NSF behavior of pile at home and abroad, works in this dissertation is completed combined with the research project supported by Hunan Provincial Natural Science Fund and Hunan Province Construction Department. By means of combination of the theoretical analysis, the field test and numerical simulation, the main original work includes;1. Actual loading sequence of NSF in pile is analyzed, loading sequence is defined into two condition: soil surrounding the pile subside first, working load applied after settlement of soil stabilized and working load applied first, soil subside after settlement of pile stabilized. Based on loading sequence definition and shear-deformation method, proposes the relative calculation method for NSF pile taking working load and loading sequence for load-transfer analysis into account for the first time. Compared with the result of finite element method analysis, it is proved that this method is reliable theoretically.2. Movement rules of NSF of pile change as changes of working load and consolidation time of soil surround pile can be obtained by not only theoretical analysis in this thesis, but also the field test and finite element analysis.â‘ Settlement of pile is least, downdrag caused by NSF is supreme, the location of neutral point is lowest without working load. Settlement increase, downdrag decrease and the location of neutral point move up evidently while working load acting upon the pile. The difference of these indexes increases as working load increase.â‘¡In the initial stages of consolidation, location of neutral point of pile with working load change from shallow to the deep position, neutral point of pile without working load change from deep to shallow position. Working load applied on the pile postpone appearance of NSF, reduce the additional axial force caused by negative friction and increase additional settlement.3. The parameters that affect the NSF behavior of pile are analyzed and discussed by Finite Element Method, following conclusions on load-transfer mechanism of NSF pile are found:â‘ Changes of loading sequence would induce the difference result. When negative skin friction appears first, additional settlement and downdrag are smaller, position of neutral point is lower, compared with that of working load applied first. The differences of these parameters increase as working load increasing.â‘¡Elastic module of pile is an important factor that affect NSF behavior of pile. Elastic module of pile that affects NSF character exist the critical value. Influences of Elastic module of pile on NSF behavior may be neglected when module of pile is greater than critical value. Compression deformation of pile increases while module of pile is lower than critical value. It makes neutral point move upwards and maximum additional stress in pile play down.â‘¢Working load applied to the pile also change the NSF behavior of end-bearing pile, but it is regarded as that the NSF behavior of end-bearing pile is hardly changed formerly. Compared with that without working load, effect of load applied to the pile make additional settlement increase, downdrag decrease and position of neutral point move upwards. The differences of these parameters increase as working load increasing.4) The NSF behavior of reinforced pile in composite foundation is analyzed by Finite Element Method under the condition of groundwater descending, following conclusions are found:The NSF in reinforced pile of composite foundation is much more evident while groundwater descending, settlement of reinforced pile and foundation, axial force in reinforced pile and pile-soil stress ratio increase in evidence. Both composite foundation with and without cushion behave similar situation while groundwater descending. In composite foundation, the disadvantageous effect of NSF induced by groundwater descending is greater than that in general use in reinforced pile.
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