Study Of Calculation Method Of Negative Skin Friction For A Single Pile In High Filled Compaction Embankment

With the development of exploitation in China west and city construction,more and more littoral and Mountainous cities take reclamation,mountain shaving and valley filling as an effective way to satisfy the requirement of construction land.Although the high filled embankment are compacted in layer,the settlement still remains.The influential factors leading settlement include:initial subgrade,kinds of filling,compaction method,degree of compaction and effect of drain etc..It's possible taking the compacted high filled embankment as subgrade directly when the structural can satisfy the magnitude of settlement.It's necessary installing piles in high filled embankment under the circumstances of the very high filling,greatly different of geological conditions in construction site,very heavy load in above structural,sensitive to settlement etc..The negative skin friction will be developed under the condition that the piles settle more than adjacent soil.The magnitude of negative skin friction on piles has indispensable effect in cost of construction and safety of structural,so the problem of compaction effect and negative skin friction on pile after compaction in high filled embankment become incredibly vital.There are two most important parameters in estimating negative skin friction in high filled embankment:1)the methods and effects of compaction and 2)the magnitude of adjacent soil.Therefore,the paper presents the study of above two most important parameters.The investigation is based on the project of constructing chemical plant in Nanchong,Sichuan province.There are two aspects in studying the research:1)design dynamic compaction parameters in order to reduce negative skin friction in high filled embankment,and optimize the parameters from design optimization via studying the relationship between dynamic compaction level and laboratory Compaction test for Optimum moisture content and construction optimization via the magnitude of settlement testing degree of compaction to control effect of dynamic compaction in order to guide the field construction,2)investigate the changing laws of negative skin friction in high compacted filled embankment via field and laboratory tests,deduce the calculation method of negative skin friction considering consolidation time via field tests and deduction,study the design method of controlling negative skin friction by controlling settlement via numerical simulation.Based on the analyses,there are following conclusions.(1)The number of hit of Compaction test has a great impact on Optimum moisture content,and the number of hit of Compaction test should be identified by the principle that single hit energy in field equals in laboratory.Using the fitting formula between magnitude of settlement ?h and degree of compaction ?c to control degree of soil,the mean error between the field degree of compaction and fitting formula is approximately 3.25%,which instructs it's feasible using the fitting formula to reckon degree of soil according to settlement.(2)The skin friction of three tested piles in untreated filled layer present the change law "negative-positive".The negative skin friction develops in untreated filled layer.The range of negative skin friction of end bearing pile is larger than friction pile.The adjacent soil supply approximately mean maximum negative friction is 9 kPa on friction piles and 3.9 kPa on end bearing pile in the depth of 7?11m.The maximum negative skin friction is 24.4 kPa on friction piles and 30.4 kPa on end bearing pile in the depth of 11?15 m.(3)The positive skin friction will translate into negative skin friction in untreated filled layer with the increasing of consolidation time.Therefore,it's vital to consider the adverse effect of negative skin friction induced by consolidation time in untreated filled layer for high filled embankment.(4)The dragload induced by negative skin friction increases with consolidation time,and the amplitude decreases gradually and tends to stable,and the dragload is larger about 41.2%?55.4%in end bearing pile than friction pile.Therefore,the friction pile can decrease adverse effects to bearing capacity of pile for high filled embankment.(5)According to load transfer method,acquire formula of calculating negative skin friction by theoretical deduction,and solve the formula by using finite difference method and get the value of negative skin friction.The tendency of skin friction from above formula is corresponding to the field test values,and the mean error of neutral point depth by calculating is approximately 12.9%comparing filed tests,which can satisfy the requirements of engineering basically.The negative skin friction by calculating is about 2 times than field tests,but requires more engineering to verify and takes the negative skin friction by calculating multiple reduction coefficient 0.6 when uses it in practice.(6)Build finite element pile model for high filled embankment using the software of MIDAS GTS NX,study the law of settlement of pile,adjacent soil under different thickness filling,pile axial force,negative skin friction,acquire rational,economic improving depth of filling,choose dynamic compaction level according to the improving depth of filling,build the design method of negative skin friction by controlling adjacent settlement.