Deep undrained failure mechanism of high-fill slopes on saturated grounds: centrifuge tests versus finite element limit analysis

Abstract

The failure of high-fill slopes in the construction of airports, roads, and dam embankments may lead to significant human and economic losses. Rapid placement of fill with limited consolidation on saturated, low-permeability ground can trigger deep-seated landslides under undrained conditions. Prior studies on this deep undrained failure mechanism have primarily focused on low backfilled embankments. In cases with fill heights exceeding 20 m, it remains challenging to assess the stability of high-fill slopes on saturated grounds. To investigate the failure mechanism of the deep-seated landslides, a pair of centrifuge model tests based on the “modeling of models” method were conducted on a backfill slope over reconstituted saturated grounds. A similar failure mechanism of deep retrogressive flowslides was observed in both models. The landslides originated in the saturated ground beneath the slope face and foot, where increased gravity induced high excess pore water pressure, reducing the effective stress nearly to the level of static liquefaction. When these two plastic failure zones, located beneath the slope face and toe, merged into a deep flowslide surface, the deeply situated plastic failure caused the high backfills above to slide downward. Finite element limit analysis (FELA) and limit equilibrium method calculations, based on three undrained strength parameters obtained from soil mechanics laboratory and in situ miniature vane shear tests, were performed to validate the failure mechanism observed in the model tests. Finally, the failure assessment of a high-fill airport embankment was performed based on the validated FELA method. The results indicate a high risk of deep-seated undrained failure mechanisms in the original ground, with the depth of such failures closely related to the relative strength of the original ground compared with the backfills.