Protection of Offshore Structures against Underscour

This paper summarizes the results of several investigations of underscour, which can endanger offshore structures. Reproduction at model scale of an unusual pattern of scour, a general lowering of the seabed under and around the whole structure, as first observed by divers, led to improved understanding of the phenomenon. Theoretical studies predicting this type of erosion, which contrasts with the usual bridge-pier type, are cited. Flow through the permeable seabed from high pressure zones under wave crests to low pressure zones under the troughs assists the local velocity in rapidly eroding the seabed. The use of reverse filters is indicated. Model tests, special severe erosion studies, and experience with offshore installations show how effective and economical protection can be obtained.