Experimental And Numerical Simulation Study On Bearing Capacity Of Pile Group Foundation Under Vertical Load

With the implementation of infrastructure construction in a large scale in China,construction of high-rise buildings and large bridges are developing rapidly, these structureshave very high requirements for settlement control and bearing capacity, traditional types offoundation cannot meet these requirements, so the pile group foundation has emerged anddeveloped rapidly as a typical type of deep foundation. Being different from the traditionalshallow foundation that bears the structure load directly by foundation soil, hard rock layer isusually chosen as the bearing layer of pile group foundation, and the load is transferred to thedeep soil with relative high concentration, it is particularly suitable for soft soil of highcompressibility, characteristics of the reinforced zone is in line with the characteristics ofstress field and displacement field of foundation, it has been proven to be a economical andeffective kind of foundation in improving safety and reducing the settlement of foundation.This paper firstly reviews the general researching situation of single pile, pile groupfoundation, pile cap and the soil around pile at home and abroad, on the basis of which, theworking properties and calculation methods of the bearing capacity of pile group foundationunder vertical load are expounded, two conventional calculation methods of the settlement ofpile group are introduced and analyzed, the scope of application is also discussed.Relevant physical parameters are determined through laboratory soil test, on the basis ofwhich, indoor model experiments of the bearing capacity of single pile and pile groupfoundation under vertical load are designed and conducted. By measuring the strain along thepile and the settlement of the top of single pile and pile cap of pile group foundation, bearingcapacity and settlement character of single pile and pile group foundation of two differentcorner-pile spacing are studied and analyzed. On the basis of model experiments, finiteelement software Midas/GTS is used to conduct the numerical simulation of the bearingcapacity of quincunx pile group foundation under conditions of five different corner-pilespacing, changing rule of the bearing capacity of pile group like settlement, axial force alongthe pile body, axial force at the top of pile and pile tip resistance are analyzed. Through themodel experiments and numerical simulation, the following conclusions are acquired：(1) Load-settlement curve of single pile and pile group is respectively steeply and slowlychanged, with the spacing of corner-pile increases from2.5D to6D, settlement of pile groupfoundation decreases, but when it increases to8D, the settlement becomes larger, so considering from the angle of controlling settlement, the spacing of corner-pile is better to beset as6D.(2) Axial force of single pile and pile group decreases nonlinearly along the depth, withthe increase of loading, the decreasing rate of axial force becomes bigger, axial force at thetop of corner-pile is larger than that of central pile, but the gap decreases with the increase ofcorner-pile spacing; there are two peak values of side friction in single pile and pile group inthe range of depth, side friction of each pile in pile group presents a “B” shape along thedepth, and the maximum value appears at the position of one third along the pile body.(3) When the net area of pile cap is constant, the load sharing amount of pile capapproximately increases linearly with the increase of load, load sharing ratio of pile capdecreases with the increase of corner-pile spacing; tip resistance of each pile increases withthe increase of load, but decreases with the increase of corner-pile spacing, tip resistance ofcorner-pile is larger than that of central pile, but the gap decreases with the increase ofcorner-pile spacing, and when the corner-pile spacing increases to8D, the gap is significantlyreduced, the sharing ratio of tip resistance to axial force at the top of corner-pile and centralpile presents a trend like this: decreases firstly, then gradually increase and comes to a stablesituation at the end.