Stress Characteristics and Failure Mechanisms of Plain Concrete Piles of Composite Foundation under Embankment

In order to reasonably analyze the stability of embankment supported on composite foundation with plain concrete piles in soft clay area, centrifugal model tests and simulation analyses were conducted to study the stress characteristics of the piles with different spacings under embankment, and a one-by-one exiting method of piles due to rupture breaking was introduced to investigate the failure modes of the piles. The results show that the stress characteristics and failure modes of the piles under embankment self-weight and train load have significant pile spacing effect. While the ratios of the pile spacing to the pile diameter are 4 and 6 respectively, rupture occurs to the first column and the first and second columns of the plain concrete piles close to the embankment toe. With a constant pile spacing, the maximum bending moment and shearing force of the piles increase with an increase in the upper load. When train loads are applied on the embankment surface, piles bear a larger maximum bending moment and shearing force with a closer distance to the embankment toe. When the pile spacing increases from 3 to 6 times the pile diameter, the maximum bending moment of piles increase from 172.9 to 601.0 kN•m, much larger than the ultimate bending moment value calibrated by test; meanwhile, the maximumshearing force of piles increase from 89.4 to 249.1 kN, much less than the ultimate shearing force value. This indicates that the plain concrete piles of composite foundation under embankment in the centrifugal model are governed by bending failure other than shear failure, tension failure or compression failure. Therefore, the piles closest to the embankment toe fail first; then, failure developing towards the embankment center, piles fail one by one in bending failure mode.