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Coastal Engineering: Theory and Practice
For surging breakers
Ns = 6.2P6018
V cot
(8.32)
Nw is the number of waves, Pb an overall porosity of breakwater, Pb = o.i
for armour layer over an imperméable layer, Pb = 0.4 for armour over a filter
layer over a coarse core, Pb = 0.6 for structures built entirely over armour
stone, Sd is the damage level and
is the surf similarity parameter.
8.5.3 Underlayer
The pur pose of underlayer is to support armour units. It is designed so that
armour units should not penetrate through the voids of the under layer.
Z>15 (armour) < 5 7?85 (underlayer)
The size of stone in under layer will be considered from W/10 to IV/15
(as per CERC, 1984). Rough angular quarry stones are considered for
underlayer in most cases for which Wr = 2650 kg/m3.
8.5.4 Core layer
The purpose of under layer is to support armour units and underlayer. It
is designed so that the underlayer units should not penetrate through the
voids of the core. It prevents the pénétration of the waves and sédiment. It
avoids the sédiment passing through it.
P15 (underlayer) < 5 Encore).
The size of stone in core layer is taken as W/100 to W/225 (as per
CERC, 1984). The rough angular quarry stones are considered for core
layer in most cases for which Wr = 2650 kg/m3.
8.5.5 Toe mound
It provides stability against scouring and sliding. Its principle function is
to support the armour stones as well as scour protection.
The size of stone in toe mound is taken as W/10 to VF/15 (as per CERC,
1984). The rough angular quarry stones are considered for the toe layer in
most cases for which Wr = 2650 kg/m3. The thumb rule to adopt the width
and the thickness of the toe berm is 37? and 2D, respectively.