| 摘要 |
A breakwater comprised of an array of aligned perforated-wall caissons having a slab bottom standing on a pervious rubble base and anchored by its own weight incorporates exceptionally heavy ballasting to ensure stability under attack by large waves, i.e. to that the ratio of maximum horizontal trust force to downward vertical force is below about 0.46. The immersed wall height is much reduced so that the slab bottom lies below mean sea level about 1.3 to 1.7 times the height of the greatest wave predicted, lessening costs of construction and siting. Efficient energy dissipation function is preserved by placement of augmenting mass below the height of the wave trough and by providing flow passages for jets directed by front wall ducts, avoiding increase of reflection coefficient. The mass may be a pervious rubble store, or a lower-grade concrete case about horizontal pipe ducts extending into or wholly through the chamber, or may be metal slabs supported on racks, or may be apertured fairing bodies carried on the front wall. Double-sided breakwaters on coasts where wave incidence occurs only at high tides incorporate a large proportion of ballast mass; when oriented as groins to protect a river mouth, the porting of an intermediate wall allows sands to migrate freely through without accretion. The rubble base comprises a core of gravel capped by larger rubble.
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