Rockfall at Toyohama Tunnel, Japan, in 1996: effect of notch growth on instability of a coastal cliff

This paper discusses the stability analysis undertaken on a 11,000 m³ rockfall at Toyohama Tunnel in 1996. It is considered that this rockfall resulted from slab failure caused by shearing, with the sliding plane passing through the deepest part of the notch formed at the cliff base. The slope stability analysis was carried out using Culmann's analysis and the measured properties of the Middle Miocene hyaloclastic rocks which form the cliff. It is shown that the cliff reaches a critical condition when the depth of the notch is some 2.5 m, corresponding with the approximately 2 m estimated from photographs. Electronic Publication