The Research On Bearing Capacity And Deformation Of Pile Group Foundation Under Vertical Load

With the acceleration of urbanization process, more and more high-rise buildingsappeared in China. As one of the main forms of foundation in the constructionengineering, the adoption rate of pile foundation is rapidly increasing. At present,there are many problems during the research of pile group foundation whether intheoretical analysis or engineering practice, so much work is needed for further study.The bearing capacity and settlement of single pile can be achieved through thepile static load test, but field static load test of pile group foundation is difficult tocarry out because the limitation of funds or equipments. At the same time, thebearing capacity mechanism of pile group foundation and interaction between pilesand soil is complex, there are still large gaps between the theory research andpractice. The development of computer technology and large advances inengineering analysis software provide a convenience for the study of pile groupbearing mechanism. A detailed calculation and analysis to the bearing capacitymechanism of pile group foundation and interaction between piles and soil undervertical load is carried in this paper, by the field static load test and numericalsimulation.The following conclusions may be arrived：(1) Compared the results of field static load test and numerical simulation,FLAC3D simulates the interaction between the soil and pile well, and the same toload transfer mechanism, by adopting reasonable geotechnical parameters especiallyparameters such as interface cohesive force and the friction angle.(2) Deformation modulus of soil play a leading role in the settlement of the pile,the influence of the internal friction angle, cohesive force is small; The main factorsinfluencing the interface bonding performance is cohesive force of the interface, theinfluence of the friction angle is small.(3) The difference of stress between piles in different positions will reduce whilethe pile spacing increases; stress distribution on the top of the pile tend to be uniformwith the increase of load, the impact on the pile bearing capacity can be ignoredwhen pile spacing Sa>6D. (4) The influences of soil characteristics on bearing capacity of pile group andsoil resistance value were significant. The bearing capacity of pile group and soilresistance value increased with the modulus of deformation increasing. But when themodulus of deformation reach a certain degree, the bearing capacity growth of pilegroup slows. So the bearing capacity of pile group can be increased by improvingthe modulus of deformation, but has a limit.(5) The proportion between pile compression and pile top settlement is verysmall for bored piles in addition to the super-long pile, longitudinal stiffness of thepile have little impact on bearing capacity, settlement and pile-soil load share ratio. soit’s enough to meet the requirement of the pile shaft when choosing pile material.Increase bearing capacity of pile group by improving elastic modulus of pile is not theright choice. The bearing capacity of pile group can significantly increase as pilelength increases, at the same time, cost control needs to be considered. The shaftfriction is full used when length-diameter ratio L/D=20～30, the specific length needsto be determined according to the engineering geology condition, the designrequirements of bearing capacity and settlement of pile group foundation.