J.A. Zwamborn, D.J.P. Scholtz, H. Claassens


Stability model tests and prototype breakage tests were done to provide data for the optimum design of dolos breakwater armouring. Stability tests with irregular waves were done with dolosse with waist ratios of 0,33, 0,36, 0,38, 0,40 and 0,43 and breakwater slopes of 1:1,33, 1:1,5 and 1:2. All model dolosse had a mass of about 80 gr and were placed at a 'normal' density, 0 = 1,00. The results showed that regular waves with H g = 1,1 H must be used to get similar damage. Also, a significant reduction in stability is evident for dolosse with larger waist-to-height ratios and for the shorter period waves (Figures 4 and 5), Some 50 9 t dolosse, without reinforcing and with different types of simple rail reinforcing, were tested for breakage behaviour, using a specially developed cushioning device to closely represent breakwater conditions. The results showed that unreinforced dolosse can withstand falls up to 1,5 m, without breakage and X or double-V rail reinforced units about double this height. The results of these tests, together with specific model tests, were used to design an effective protection for the Table Bay main breakwater. The tests indicated the use of 25 t dolosse (minimum) but, because of the shallow waterdepth, the toe dolosse of the repair slope were reinforced (double-V rail reinforcing), stabilized by 75 mm steel chains, and bitumen grout will be placed to reduce their movements.


dolos; dolos stability; dolos; behavior

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