Centrifugal model tests on failure mechanisms of embankments on soft ground reinforced by rigid piles

Centrifuge tests are carried out to study the embankment supported on the rigid pile composite ground. For all the test models, the upper layer of the ground is soft clay and the lower layer is stiff sand. The cases of using single-row piles and group piles are considered. The deformation behavior, load transfer and failure mechanisms of the piles and embankment are investigated with different pile bending stiffnesses and strengths, piles locations, pile spacings and embedded depth of pile toe into stiff stratum. The centrifuge tests show that in all the cases, the maximum bending moment of piles is located near the interface of soft and stiff strata. For the embankment on group piles, the closer to the embankment center the pile is, the smaller the bending moment is. When the piles have a high bending stiffness and strength, a large spacing, and a sufficient embedded depth into stiff stratum, soil may flow around the piles, which will lead to the overall failure of embankment. In contrast, for the single-row piles with a low bending stiffness and strength, the piles will fail firstly by bending failure mode at the interface of the soft and stiff strata, and then the secondary bending failure may occur at the upper part of the pile before the embankment failure. For the group piles with a low bending stiffness and strength, some piles near the embankment toe would also fail firstly by bending failure mode at the interface of the soft and stiff strata. Besides, the tensile failure may break the pile into two parts. In the final stage, the collapse failure or the secondary bending failure of the pile upper part will lead to the overall failure of embankment. According to the failure mechanisms of embankment, the embankment stability may be enhanced by the measures of increasing pile bending strength, decreasing pile spacing or increasing the embedded depth of pile toe into stiff stratum.