Abstract:

Bending failure is a normal damage model of pile foundation in earthquake. An important reason of this model is the deficiency of pile’s flexural stiffness. To a certain length, the flexural stiffness is immediately relate to pile’s slenderness ratio. But in the pile foundation criterion, there has no limitation for friction pile’s slenderness ratio like end bearing ones. On the base of structural dynamic model of saturated loess, the finite-infinite element model of single friction pile-soil-structure system and end-bearing pile-soil-structure in loess area are established by finite element program. The influence of slenderness ratio on the system’s dynamic characteristics was studied; and the regulations were as follows. Firstly, when other conditions are the same, no matter end bearing pile or friction ones, the slenderness ratio has a little influence on the distributions of pile section’s shearing stress and pile’s horizontal acceleration. But along with the increase of slenderness ratio, the shearing stress reduces while the horizontal acceleration increase. Secondly, along with the increase of slenderness ratio, the pile’s deformation type transits from normal flexure model to contraflexure model gradually. Accordingly, the pile’s damage model transits from shearing failure to bending failure. Thirdly, the end bearing pile’s deformation curve is more likely to behave as contraflexure model than friction ones. But when the slenderness ratio arrives at a certain value, the friction pile also can behave as contraflexure model. In the aspect of seismic resistance, the appropriate limitation of friction pile’s slenderness ratio is which can make the pile’s deformation curve behaves as normal flexure model. The conclusions can give instruction for engineering practice in the future.

Key words: saturated loess, structural dynamic stress-strain relationship, pile-soil-structure system, finite-infinite element, dynamic interaction, slenderness ratio