Base liquefaction: a mechanism for shear-induced failure of loose granular slopes

For the deviatoric strain-softening associated with static liquefaction to occur in a landslide, the soil must be contractile, be subjected to a monotonic loading trigger, and be sufficiently saturated to permit the generation of excess pore-water pressures upon loading. It is hypothesized in this paper that static liquefaction might preferentially occur in the saturated granular soil located at the base of the landslide in certain circumstances rather than the well-drained inclined portion of the slope. This hypothesis was tested using the technique of geotechnical centrifuge modelling with a loose granular slope, which was brought to failure under a step-wise increase in groundwater flux. The rising pore-water pressures eventually led to a small localized failure at the toe of the slope. This toe failure acted as the monotonic loading trigger to shear the loose contractile saturated sand at the base of the slope and cause liquefaction to occur in the base region. A back-analysis of the landslide indicates that these types of analyses should be viewed with great caution as the progressive nature of the event following triggering will be likely to lead to erroneous back-calculations of mobilized strength.