Research Of Friction And End-bearing Piles On Composite Pile Foundation

The pile foundation of building penetrating through overlying stratum down tothe bedrock (the distance that the pile penetrate into the unweathered rock is morethan 0.5 meter) is called the pile penetrating into the bedrock. The pile penetrates intothe bedrock with a high bearing capacity due to the high strength and lowcompressibility of bedrock. Meanwhile, the value of settlement is so small that thesettlement of buildings can finish during the construction. In virtue of this merits, it isused widely in engineering design, especially for high-rise buildings and large-scaleconstructions. In the practice of project, some designers consider that piles penetrating into thebedrock are all end-bearing piles, they are only have tip resistance ignoring the lateralresistance of soil layer. However, this calculational model is not conformed to theactual conditions of many projects. In fact, the pile penetrating into the bedrock havedifferent performance of bearing according to the different condition of engineeringgeology, geometrical dimension of piles and means of producing piles. It is proved bymany site-test results that lateral resistance of piles can not be ignored in manysituations. Such as, the pile whose tip bears on the bedrock, piles penetrating into thebedrock that the strength of their surrounding soil is high and the ratio of pile lengthto diameter not less than 35.A method of design has been put forward for composite pile foundation that thebearing capacity depending on friction between soil layer and pile, end-bearing of pile.This method of design is that piles are concentrated located under shear wall orcolumn and flexible cushions with a given thickness or special deforming devices areinstalled between the top of pile and raft foundation (bearing board). The soil betweenpiles carries the preload by compelling the soil between piles to settle earlier than thetop of pile. Subsequently, the pile and soil work together to bear the load. Theeconomic benefits of this method is better than that routine pile foundation andcomposite foundation because it can full use of the bearing capacity of foundation soil,reduce largely the amount of pile and steel and the thickness of raft foundation.Through the elementary research of it's bearing mechanics and the characteristic ofdeformation, the formula used to calculate approximately the bearing capacity andsettlement bas been obtained. It has gained good economic benefits with it usedsuccessfully to actual projects.