Design of Rubble Mound Breakwaters: Structural Integrity

Rubble mound breakwaters require availability of often very large quantities of rock materials of various gradings and qualities. Because natural stones are seldom available in sufficient quantities and sizes the materials must in most cases be supplied from quarries. The output from a quarry in terms of sizes and shapes is, however, not only dependent on the applied blasting technique but to a large extent on the type of rock and the degree of weathering. This creates very different discontinuity patterns which again determine the size and shape of the blocks. Also the strength and durability of the rock material are functions of rock type and the degree of weathering. Thus it is important to establish the availability and quality of rock material before completion of a breakwater design for a particular location. If this is not possible then design changes are to be foreseen during the construction stage. Anyway, it is seldom that a fair amount of rocks of mass larger than 10-15 t can be produced, even in good quality quarries. If heavier blocks are needed concrete armour units or vertical structures must be considered.