Effect Analysis Of Pile-soil Interface Characteristics On Bearing Capacity Behaviors For Nondisplacement Piles

In deep foundation engineering which including high-rise buildings, bridges,municipal engineering, ports and so on, one of the most common and economicalpile is nondisplacement piles, such as bored piles.The pile-soil interface’s contactcharacteristics of different drilling methods are quite different, the bored piles’carrying capacity is vary considerably. In this article,the pile-soil interface featuresrefer to relative stiffness, relative roughness, the contact surface deformationcharacteristics of soil which around the pile, the dilatancy and contractioncharacteristics of the soil which around the pile’s contact surface, pile diameter andsoil initial stress level, etc.This article focuses on the shear deformation characteristic of sand, especiallythe dilatancy or contraction characteristics under critical state. The scholars hadgeneralized、 calculated and analyzed the influence of shear deformation ofsoil-structure surface contact characteristics under the basis of soil-structure surfacecontact characteristic test and constitutive model. At the same time, they alwayscompared with other literature calculation results, and verified the correctness ofnumerical methods. The shear model of contact surface is a thin layer of critical statemodel (the layer thickness is namely the width of the shear), this paper makes itapplied to the nondisplacement pile. Under the foundation of the revise of transferfunction calculation method of pile load calculation, this paper analysis the influenceof the contact characteristics of pile-soil interface for pile bearing behavior, andreveals the relationship between side friction and the relative displacement of pile andsoil. At last, it also makes the pile bearing and settlement calculation much morecloser to the actual situation.The main achievements are as follows:(1) The interface constitutive model used in this paper have many modelparameters. It can describe soil-structure interface shear characteristics and reflectthe pile bearing capacity appropriately. (2) Using CNL and CNS two kinds of numerical experiments, and through theanalysis on relevant parameters influencing the shear characteristics of soil-structureinterface, we obtain: to the sandy soil, the smaller the initial pore space ratio is, thesmaller the confining pressure is; the thinner the contact surface thickness is, thesmaller the normal stiffness is; the sharper the dilatancy is, the weaker the shearcontraction is, and then the smaller the bulk strain it reaches the phase transition; tothe dense sand, the peak value of the shear stress intensity is influenced by therelative roughness of the contact surface, and the strain softening phenomenonbecomes more obvious, while, to the relative smooth contact surface, the shearcontraction characteristics is strong, the strain softening phenomenon is not obvious.(3) The distribution of nonlinear of side friction resistance of piles along thedepth is much more clearly and its peak much greater, as the relative rougher ofpile-soil contact surfaces, the increase of compaction of the soil, the greater of thevertical bearing capacity of single pile, while the playing of the pile’s lateral frictionof the need much greater pile soil relative displacement.(4) The soil around the pile experience appears contraction or dilatancyphenomenon after shearing because of the difference on the contact surface relativeroughness, the relationship between stress and strain takes on hardening or softeningcharacteristics.