Physical modelling of landslides in loose granular soils

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Beddoe, Ryley
landslides , physical modelling , static liquefaction
The catastrophic consequences associated with landslides necessitate predictions of these hazards to be made with as much certainty as possible. However, the often complex nature of these events make predictions highly challenging. In this thesis, a number of hypotheses related to the triggering mechanisms and subsequent consequences of landslides in a loose-granular soil were investigated. The investigation was conducted using small-scale geotechnical centrifuge models, and a new flume facility developed to examine landslide behavior in a reduced-scale model. The first hypothesis explored in this research was that static liquefaction might preferentially occur in the saturated granular soil located at the base of the landslide rather than the well-drained inclined portion of the slope. Using a geotechnical centrifuge model, it was found that a small initial toe failure did act as a monotonic loading trigger to shear the loose contractile saturated sand at the base of the slope and caused liquefaction to occur. The second hypothesis investigated whether the consequences of a landslide triggered under elevated groundwater antecedent conditions are higher than scenarios under drier antecedent conditions. Results from five centrifuge models subjected to different antecedent groundwater conditions show that higher groundwater conditions can result in landslides with velocities about three times higher and travel distances eight times higher than low antecedent conditions. The third hypothesis investigated the influence of slope inclination on landslide consequences. Seven geotechnical centrifuge models were built and tested, comparing the consequences of landslides triggered in 20° and 30° sloped models with different groundwater conditions. The results of these tests found that the influence of slope angle on the mobility consequences of a triggered landslide are highly dependent on the antecedent groundwater conditions. The most significant case was under high groundwater conditions, where the shallower 20° slope travelled twice the distance and speed of the steeper 30° slope. A new flume facility was developed to examine landslide behaviour in a reduced-scale model, and a direct comparison was made to one of the centrifuge models from the research. The comparison demonstrated the challenges associated with using reduced-scale models to study suction-dominated problems such as hydraulically-induced landslides in loose granular soils.
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