Study On Characteristics Of Pile-Soil Interface Based On Thin-Layer Bounding Surface Model Under Axially Cyclic Loading

The behavior ofpile-soil thin-layer interface have a significant effect on pile-soilinteraction under axially cyclic loads, the interaction of pile and soil is fundamentallyattributed to soil-structure interaction analysis which is one of the key issues ingeotechnical domain. Comprehensively and accurately reflecting the complexmechanics properties and volume change of the interface under cyclic loads is vitallyimportant for interaction of soil and structure. A more accurate interface constitutivemodel can be more helpful for illustrating the stress-strain characteristics of a pilefoundation.In this paper, the existing thin-layer bounding surface model was modified inorder to describe the strain hardening and softening characteristics either in loading orunloading process. An implicit iterative algorithm was established based on themodified thin-layer bounding surface model. Thereafter the numerical shear tests ofsand under monotonic and cyclic loading considering CNL and CNS boundaryconditions would be established. By using a modified thin-layer bounding surfacemodel as load transfer function and establishing a simple numerical model for singlepile, the bearing characteristics of pile foundation under axially cyclic load would beanalyzed. Preliminary tries would be made to realize the finite element analysisconsidering thin-layer bounding surface model under axially cyclic load. Theapplicability of using a subroutine, UINTER, on the basis of ABAQUS to write animplicit iterative procedure, would be discussed. According to the comparativeanalysis of Goodman element and Coulomb contact model, a further illustration forthe model characteristics would be given.The main conclusions can be drawn as follows:(1)The modified thin-layer bounding surface model based on the critical state ofsoil can describe the relationship between stress and strain on soil-structure interfaceconsidering hardening and softening characteristics as well as the couplingcharacteristic in normal and tangential directions under cyclic loading. (2)In general, cyclic shear stress of soil-structure interface under cyclic loadingdecreases while increasing the number of cycles and finally tends to be stable.Cumulative volume deformation increases while increasing the number of cycles, butthe growth rate decreases. Compaction and dilation occur alternately after each cycle.In the meantime, the relative trend of volume change would be affected by variousfactors.(3)The mechanical properties and volume change of pile-soil interface aresimilar to that of soil-structure interface. The degradation of pile lateral frictionresistance is largely determined by the cyclic load level, normal stress, initial voidratio and roughness etc. Cyclic loading history would change the initial state of thesoil and therefore the bearing capacities.(4)With the utilization of UINTER from ABAQUS, the FEA analysis of aconstitutive model with customized contact surface can be realized. The defaultCoulomb contact model in ABAQUS cannot accurately describe the relationshipbetween friction resistance and displacement.