Performance of a large-scale slope model subjected to rising and lowering water levels

Many slope failures have been observed to occur during times of water level fluctuations. This paper presents a large-scale model test simulating the performance of a sandy silty soil slope subjected to water level rise and drawdown. The slope model is 15 m long, 6 m high and 5 m wide, and the sloping part has an inclination of 1:1 and a height of 4 m. A water level control system was developed to allow the simulation of the rise and sudden drawdown of the water level. Pore-water pressures (negative and positive), total earth pressures, the slip surface and the landslide process were recorded during the simulation process. Data gathered under controlled laboratory conditions was useful for the verification of analytical and numerical modelling methods. Pore-water pressure inside the slope showed a significant delay relative to the drawdown of the water level outside the slope. The failure mode that developed during rapid drawdown was of the multiple retrogressive rotational type. The results provide an improved understanding of the physical behaviour and failure mode of a saturated–unsaturated soil slope subjected to water level fluctuations.