STABILITY ANALYSIS OF OLD BREAKWATERS: CASE STUDIES OF FAILURES AND SUCCESSES

Until about 1930, analysis of wave loads on vertical breakwaters was based trial and error. Russell(1) noted it unfortunate that “the young engineer …should be left to guided entirely by circumstances, without the aid any one general principle.” Stevenson(2) has always a difficulty in estimating force waves with which he contend.” Wave formulae Sainflou(3) Goda(4) improved design methods, but were 50 100 years too late for many ‘old’ breakwaters, do not apply composite – ignoring seminal influence shoals or mounds breaking impulsive loadings. This paper presents case studies using empirical methods developed over last 20-30 calculate stability example including: Wick (failed before completion); Alderney (multiple breaches during construction, only survives 1/2 its original length); Dover (survives substantial Factors Safety). The screening analysis(5) used previous 20 years(10), summarised studies(6,7). Methods here are (no numerical modelling) so calculations can easily repeated local engineers.