Study On The Degenerate Mechanism Of Pile-Soil Interface Under Cyclic Loading

The degenerate mechanism of pile-soil interface is the primary theory for for bearing capacity of pile under cyclic loading.The degenerate effects of pile-soil interface under cyclic loading consist of degenerate shear stress,degenerate normal stress,and the breakage mechanism of sand particle.All of these effects interact with each other,controlling the bearing capacity of pile-soil interface.A comprehensive research program,involving a constant normal stiffness cyclic shear test of pile-soil interface and numerical simulation of particle flow,was conducted to reveal the influence of different influencing factors on the degenerate mechanism of pile-soil interface under cyclic loading.This study includes the conclusions as follows:(1)It reveals an approximately logarithmic set-up on the degeneration of shear stress and normal stress with the increase of the cyclic number from the constant normal stiffness cyclic shear test of pile-soil interface.The degeneration of shear stress occurs mainly in the first 5 cycles,and the attenuation amplitude reaches 50% after 20 cyclic shear test.The rate of degeneration increases with the increase of the initial normal stress,the amplitude of shear displacement and the interface roughness.(2)The interfacial friction angle of concrete is greater than that of steel plate in CNS cyclic shearing test.The internal friction angle of the sand sample decreases by 10% ~ 17% compared with the original sand.The range of the median diameter of the shear bands in the interface between concrete and steel plate is 0.16mm~0.19 mm,0.19mm~0.21 mm,which are smaller than the median diameter of the original sand whose median diameter is 0.34 mm.(3)There exists the critical state friction coefficient in numerical simulation of particle flow.When the interfacial friction coefficient is less than ?cr,the thickness of shear band increases with the increase of the friction coefficient.When the interfacial friction coefficient is larger than ?cr,the thickness of shear band changes very little.The shear band thickness increases with the increasing of the initial normal stress in the same bonding force between particles.The shear band thickness decays with the increasing of the bonding force between particles in the same initial normal stress.Proposing the empirical formula of the shear degenerate factor and the normla degenerate factor by using the normalization principle.(4)In the numerical simulation of particle flow,the degeneration rate of the shear stress and the normal stress increases with the increasing of the amplitude of shear displacement in interfacial friction coefficient and the same bonding force between particles.The degeneration rate of the shear stress and the normal stress decays with the increasing of the bonding force between particles in the same interfacial friction coefficient and the amplitude of shear displacement.