ON THE DRIVING BEHAVIOR，VARIABLE－DIAMETEREFFECT AND BEAKING CAPACITY OF DRIVENCAST－IN－SITU PILE WITHFLAT

ON THE DRIVING BEHAVIOR,VARIABLE-DIAMETER EFFECT AND BEAKING CAPACITY OF DKIVEN CAST-IN-SITU PILE WITH FLAT OVERSIZE TIP

ＯＮＴＨＥＤＲＩＶＩＮＧＢＥＨＡＶＩＯＲ，ＶＡＲＩＡＢＬＥ－ＤＩＡＭＥＴＥＲＥＦＦＥＣＴＡＮＤＢＥＡＫＩＮＧＣＡＰＡＣＩＴＹＯＦＤＫＩＶＥＮＣＡＳＴ－ＩＮ－ＳＩＴＵＰＩＬＥＷＩＴＨＦＬＡＴＯＶＥＲＳＩＺＥＴＩＰＳｈｉＰｅｉｄｏｎｇ，ＦｕＺｈｅｎｑｉｕ...

he paper reviews the results of series of field and laboratory tests as well as ten odd years engineering experi-ences of using the innovation by the first author of the precast concrete FLAT OVERSIZE TIP in driven cast-in- situ pile to replace the conventional conical tip.It is presented that flat oversize tipped pile is suitable for subsoil conditions having shallow firm bearing stratum and easily to be driven into required penetration,while details of construction technology remain the same as those of conical tipped pile. In case of layered soil deposit a VARI-ABLE-DIAMETER EFFECT has been found of the flat oversize tipped pile,which results in nodular projections in stiffer soil layers along pile shaft,meanwhile the enlarged end portion in bearing stratum forms a composite base enlar gement with the precast tip.So,much higher bearing capacity is usually achieved of the flat oversize tipped pile. In bearing stratum of silty and fine sand it is twice that of conical tipped pile,and in clayey soils it reaches140% of that of conical tipped pile. Since the 1980s flat oversize tipped piles have been successfully applied to buildings up to l5 storeis in Zhejing and Jiangsu Provinces etc. in China,Besides,water towers,chimney stalks and other tall struct ures are founded on flat oversize tipped piles,Such buildings and structures as completed amount to some hundred thousand quare meters. Averagely speaking l/3 or l/2 numbers of piles compared with that of conical tipped type are saved. Due to slight group action,settlements of buildings and structures on flat oversize tipped piles are usually as small as l0～15 mm in one year after completion and they stabilize soon.Flat oversize tipped pile has recently been adopted in China National Proffessional Standard-Technical Code for Building Pile Foundation JGJ 94 94.This paper is dedicated for designers' and contractors′ reference in selecting proper safe and economical type of pile for their project according to their geologyical conditions etc