8. Design of Coastal Structures
241
effects (e.g. seawalls), the total force, Ft and moment, Mt
by the expressions
Mt = ^ + Mw
6
are to be found
(8-2)
(8-3)
8.3 Wave Forces on Walls and Rubble Mound Structures
The rubble mound and vertical types are the common Coastal structures.
The évaluation of wave forces on such structures also important.
8.3.1 Rubble mound structures
In the case of a rubble mound breakwater, like groins or breakwaters, the
size of the individual stone/armor or artificial block forming the primary
or the cover layer should be designed such that it is stable when exposed to
the action of high waves even during severe sea state. The forces acting on a
rubble stone on a slope a is schematically represented in Fig. 8.7. Equating
the different forces, we get
mg sin a + (force due to waves) = gmg cos a
(8.4)
wherein “m” is mass of stone or the armour block, g is a friction coefficient.
The diameter of stone is Dg, the density is ps and pw are the density of
water, respectively. The wave force on the armour, Fa can be expressed as
Fa = 0.5fwpwu2 • D2 • constant
(8-5)
Fig. 8.7 Forces on an armour unit in waves — définition sketch.