A Treatise On The Principles And Practice Of Harbour Engineering

BREAKWATER DESIGN. 137 systematically. They have a tendency, also, towards becoming rounded like boulders, and this does not improve their steadiness in situ. Mounds are most commonly formed in assorted layers, with the smaller material at the base and the largest at the top and on the flanks. Apart from the additional expense involved in selecting the material and of laying it in proper order, there is this further consideration, that such mounds are less compact and less solid than mounds which are formed by an indiscriminate Section of San Vincenzo Mole- Section of San Vincenzo Mole Extension. q 10 20 30 40 50 60 70 BO 9p IÇ0 Scale of feet. Fig. 115. —Sections of Breakwater at Naples. deposit of varied material, in which the smaller fragments occupy the inter- stices in the larger. On the other hand, a greater quantity of rubble is required for these cases. Stresses in Wall Breakwaters.—We next turn our attention to the magnitude and extent of the disruptive forces acting upon upright walls so far as the stresses to which they give rise are measurable in numerical terms. Considered as a structure exposed to the effects of wave action, a wall breakwater may fail partly, or wholly, in one or other of the following ways : — (1) By the shearing of some bed-joint, or by the sliding of one component block upon another ; (2) By overturning as a solid mass in sections of variable size ;