بررسي عملكرد ميكروشمع ها تحت اثر بار ديناميكي با به كارگيري مدل سطح مرزي براي شبيه سازي رفتار خاك

چكيده انگليسي :

Micropiles Behavior under Dynamic Loading Using a Bounding Surface Constitutive Model for Soil Matrix Neda Motamedi neda motamedi@cv iut ac ir Date of Submission 2011 06 14 Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Amir M Halabian mahdi@cc iut ac irAbstractMicropiles are generally described as small diameter maximum 300mm drilled and grouted piles They canwithstand axial and lateral loads while they can work as a component in a composite soil pile mass or as asubstitute for conventional piles Due to their geometry the load transfer mechanism for micropiles is mainlygoverned by shaft resistance rather than end bearing Micropiles are being increasingly used in somestructures which are subjected to different type of dynamic loadings Dynamic loadings are often variable innature in terms of amplitude and frequency that could result differing types of micropile behavior leading tovariably failure mechanisms This research aims to numerically investigate micropiles dynamic behaviorunder axial cyclic loading Having a constitutive model that can simulate soil matrix behavior under differentstress paths utilized in a given numerical technique is an essential task For cohesionless soils stress dilatancy and cyclic behavior are among the important aspects of soil behavior states that should beaccounted for in the constitutive model A constitutive model based on the bounding surface plasticityoriginally proposed by Manzari and Dafalias 1997 was adopted in this research to simulate the dynamicbehavior of the soil matrix The model combines bounding surface plasticity and Row s dilatancy theorywithin critical state concepts Dilatancy is modeled by choosing a proper function for cohesionless soils Onecan name some distinct features of the model as its capabilities to describe the principle aspects ofcohesionless soils such as mean stress and loading path dependent dilatancy hardening and softening aswell as initial and induced anisotropy The effect of fabric formation on the unloading response of saturatedsand was also taken into account having a fabric tensor incorporated into the dilatancy formulation Themodel requires a unique set of material constants for a particular soil at a given density and confiningpressure A semi implicit stress point algorithm was used for the integration of the constitutive stress strainrate equations The proposed numerical scheme was coded in FORTRAN and used to simulate a variablymonotonic and cyclic soil experiments for verification purposes The same numerical algorithm was alsocommanded as a VUMAT file in a commercial FEM code ABAQUS Different numerical models for soil micropile systems using ABAQUS Explicit were developed to study the effect of parameters such as theamplitude and frequency of dynamic loading magnitude of initial static loading and different states of sandysoil matrix on dynamic response of micropiles The results indicated that loading frequency has importantrole in the microplies induced displacements In addition having the initial static load increased moredisplacement will occur under dynamic loading Keywords Micropiles Dynamic loading Bounding surface model Numerical implementation Cutting plane method

معتمدي، ندا

بررسي عملكرد ميكروشمع ها تحت اثر بار ديناميكي با به كارگيري مدل سطح مرزي براي شبيه سازي رفتار خاك

پياده سازي عددي , روش صفحه برشي