Study On The Single Pile’s Load Bearing Behavior Of Precast Prestressed Spun Concrete Square Piles

In 2003,Precast prestressed spun concrete square piles(short for:hollow square pile)as a new type pile was developmented by China Academy of Building Research(CABR),it is development on the basis of prefabricated square-pile and prestressed pipe pile.For the pile body,the section shape is square,the internal hollow section shape is circular;the steel skeleton is compose of prestressed steel casted in internal concrete and spiral hoop winded in prestressed steel,two pieces square steel plate are respectively fixed and connected to the pile ends,and there are some anchorage holes used to anchor prestressed steel in the square steel.After pretensioning prestressed,centrifugal shaping,high pressure steam keeping and other production process,the precast prestressed spun concrete square piles was produced as a kind of prestressed concrete memberssquare.Which external is square and internal is circular;it has equal and hollow section.Hollow square pile has some characteristics,such as large bearing capacity of single pile,excellent pile quality,good integrity,transportation and construction is convenient,low breakage rate of pile construction,good seismic performance,flexible making mode and so on,it is a new and excellent type pile,which is better replacement of pipe sinking cast-in-place pile,hollow pile,prestressed concrete pipe pile,part of bored pile,at the same time,the kind of pile can reduce weight,saving materials,raise economic benefits because of its hollow structure.At present,hollow square pile is popularization and application in practical engineering,in contrast,the research on the bearing behavior of hollow square single pile is little in the domestic,there are still some urgent problems need to be solved in the field of technique promotion,popularize and application of hollow square pile,for example,the theoretical depth is not enough,design based is imperfect,some properties just like loading transfer behavior,settlement and failure characteristics are not fully determine.Based on the static load test of hollow square pile and prestressed pipe pile,in this paper,the hollow square pile’s bearing behavior is analysis through using theoretical analysis and numerical calculation,the main contents are as follows:(1)Through comparative analysis the results of the static load test and high strain test about hollow square pile and prestressed pipe pile under same soil condition,ii show that,hollow square pile Q-s curve is relatively flatter,latter pressure bearing capacity is stronger,ultimate bearing capacity increased by 10%,moreover,the resull of high strain dynamic test and test values are almost consistent,it can be used in engineering practice.(2)The load transfer model of hollow square pile and prestressed pipe pile is established by using load transfer function method,meanwhile,related parameters of the model are calculated and selected,the Q-s curve and axial force of two type pile are calculated by advanced programme language,compare the calculation and static loading test results,it shows,the method is reasonable and feasible,which can partly or totally replace the static load test.(3)Using the MIDAS/GTS to stimulated and analyzed,the result compare to the test and calculation results,shows,the simulation values are almost same with test values and calculation values,moreover,the effect on the soil around hollow square pile is more significant,the deep and wide range of influence of funnel type pile is larger and deeper.(4)Economic analysis shows that:the cost of hollow square pile reduce 10%,the cost of hollow square pile cap reduce 10%.