Report No. : GEO Report No. 47

Report Title : Stability of Submarine Slopes (1995), 51 p.

Author : N.C. Evans


This report presents a comprehensive review of overseas literature on the stability of submarine slopes and the application of analytical techniques to typical submarine slopes in Hong Kong waters. The report also looks at the sea bed in Hong Kong in a regional context, describing the water circulation patterns and depositional environments in the area, and examining the probable impacts of these reginal factors on submarine slope stability. Two main types of slope have been considered, namely, natural seabed slopes and dredged slopes (cut slopes).

The existing natural seabed topography of Hong Kong may be regarded as generally stable and as being in a state of dynamic equilibrium with the generally mild erosional/depositional environment. Civil engineering works which change the natural topography and/or hydrodynamic regime can be expected to have a greater effect on submarine slope stability than natural events. Extreme natural events may, however, exacerbate any inherent instability caused by engineering works.

Study of natural slopes off North Lantau confirms tha the existing seabed is in equilibrium. Seabed topography in shallow water in this area has been shown to be related to long term (1,000 year) wave height and water level conditions.

Comparison of observed and predicted maximum gradients in dredged borrow pits in Urmston Road, and in test cuts at Plover Cove, suggests that theoretical methods can be used to give reasonable predictions of short to medium term stable dredged slope angles. These angles will vary with soil properties and site characteristics, i.e. water depth and wave regime.

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