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Failure of Gansbaai Leeward Breakwater:
Fines Washout from Breakwater Core
by
MIKE CHEMALY
Pr. Eng, B. Eng, M. Eng
WSP Africa Coastal Engineers
PO Box 413
Stellenbosch
South Africa
Tel.: +27 21 883 9260
E-mail: mike.chemaly@wspgroup.co.za
KEY WORDS
Wash out, fines, breakwater core, failure mechanism,
single layer rock
MOTS-CLEFS
m and Ch 126 m armour rock from the crest, slope
and toe had been removed by wave action.
Breakwater failure is attributed to two separate
failure mechanisms, as described further on in this
paper.
Erosion massive, fines, noyau, mécanisme de
rupture, simple couche d’enrochements
1. INTRODUCTION
Gansbaai is situated along the South African
coastline approximately 65 km northwest from the
southernmost tip of Africa. Gansbaai’s New Fishing
Harbour was constructed in two phases over
a period of almost 20 years. Phase I was between
1965 and 1969. Phase II commenced in 1979.
The wave height regime in this part of the world is
severe. Wave heights in the order of 8 m to 9 m
within a few hundred metres just offshore of Gansbaai’s
New Fishing Harbour are not uncommon
during an average winter season.
The Leeward Breakwater to Gansbaai’s New Harbour
is 200 m long. Structural failure over 60 m of
breakwater length initiated emergency repairs to
this section of the breakwater. Complete breakwater
failure between Ch 66 m and Ch 96 m (30 m
length) and rock armour structural failure between
Ch 96 m and Ch 126 m (30 m length) took place.
Between Ch 66 m and Ch 96 m all armour rock
and core material was washed out. In the process
the concrete roadway collapsed. Between Ch 96
11
Gansbaai – South Africa
Gansbaai – New Harbour and location
of damage
PIANC E-Magazine n° 144, November/novembre 2011