Investigation of Structural Behavior of Piles in Liquefiable Cohesionless Soils

Abstract

Piled foundation design and behaviour under static and dynamic loading (wave motion, earthquake, wind, vibration loadings of machinery) conditions are study subjects that are focus of interest recently in the geotechnical engineering applications. Liquefaction can be described as strength and stiffness loss of a loose, saturated non-cohesive soil under undrained cyclic loading as a result of increasing pore water pressures which reduce effective stress. Large deformations and lateral flow occurring in the layers of liquefied soil during earthquake could lead to strength and stiffness lose which may result with pile buckling and considerably increased earthquake damage on the superstructure. Predicting the bearing capacity and the deformation shape of the piled foundations during the earthquake is essential for the economy and the structural safety of the design. In this study model pile tests are conducted in uniform sandy soil and pile structural capacity is investigated under the effects of relative density and degree of saturation of surrounding soil, and pile embedment depth. Steel rods were used to represent the piles in the model tests. Sand soil was placed in a cylindirical tank at different thicknesses to provide for different pile embedment depths. Soils were compacted at four different compaction level to provide relative densities in the range of 45-80%. Static incremental load has been applied on the upper plate of the pile system in the tests. While the increase in the relative density affects the structural capacity of the piles positively, surrounding soil being saturated has resulted with capacity losses. Experimental results show that there is a consistency between our experimental findings and literature about deformation shape and buckling length of piles in liquified soils.