8. Design of Coastal Structures
275
Sustainable significant wave height = Hmax/1.8 = 4.72 m <
feo = 5m
Thus, wave could break on the rubble mound and the structure should
be designed for breaking condition having a design wave height ÇHdes) of
4.72 m.
Armour layer design: (Hudson formula)
N, = -^- = (KDœte)i
^a-^a
Let, = 2.65 t/m3; yw = 1.025 t/m3,
△a = ( ^-- 1 ) = 1.585.
\7w
/
Kd = 2 for breaking condition (CEM, 2006) for a random rubble mound
structure with a side slope of cot# = 2.
Weight of the armour stone (VE),
W50 = „7'8 AVe\ a = 17.49 ton
ApAg cot#
Adopt W50 = 18 ton with a gradation of (75% to 125%) VE50, i.e., the range
of armour layer stones is 13.5 ton to 22.5 ton and placed in two layers.
Thickness of armour layer
tarmour = nK&Dso
where, n is the number of layers and the layer coefficient, K& can be
obtained from CEM (2006) for different types of armour units and D50
is the characteristic dimension of an armour unit.
The characteristic dimension of a single armour unit is defined as the
équivalent diameter, defined as,
i.e.,D$o = 1.89 m
Let,
= 1, then, tarmour = 3.787 m.