Concern over loosely compacted fill slopes stability in Hong Kong has been aroused in the past few decades, since the Sau Mau Ping disasters of 1972 and 1976. Research conducted on loose fill slopes in the past few years aimed to understand the failure mechanisms of a loosely compacted fill slope. Recently, layering effect has been hypothesised to be a possible condition in the fill slopes to induce a fast flowslide associated with a rise of watertable. However, the failure mechanisms of layered fill slopes subjected to such a rise are still not fully understood.
Completely decomposed granitie (CDG), a typical soil found in Hong Kong, was used for the centrifuge tests of loose fill slopes. The use of 10 m beam centrifuge with the assistance of a newly purchased high speed camera in the Schofield Center of Cambridge University Engineering Department (CUED) makes it possible to investigate the significance of layering effect in a loose fill slopes and hence the triggering mechanisms of loose fill slopes.
Seven model slopes were made and tested at various gravity levels and conditions. The behaviours of a layered fill slope subjected to a rise of watertable were measured in terms of soil deformation and pore water pressure. In the centrifuge tests, shear localized progressive failure is visualized by means of an image analysis developed by CUED. The experimental results showed that layered fill slope are highly susceptible to failure and this effect should not be overlooked. Proper drainage arrangement in a fill slopes should be considered for the preventive measures.