242
Coastal Engineering: Theory and Practice
Herein, fw is the friction factor and on assuming a long wave acts on
the armour, “u” can be u = constant, (gHb)1/2. Hence, the design massof
stone M can be calculated as,
___________ PsHb____________
FCp(ps/Pw - l)3(/^cosa - sina)3
The breaking wave height, Hb can be assumed to be the design wave
height, Kd as a constant that takes into account the characteristics of
the armor layer and ps and pw are the densities of armour layer for e.g.
rock and sea water, respectively. However, the formula of Hudson (1959) is
being widely adopted for obtaining the weight of the armour block which
is given as
w=_____11Kb. _____
(871
KD(Sr-l)3COte
where Hd is the design wave height in “m”,
is the unit weight of the
armour unit, 6 is the angle of revetment with the horizontal, submerged
weight of the armour, Sr = (Ps/Pw — 1)- Kd is a dimensionless stability
coefficient, determined through physical modelling. This value for Kd vary
for different kinds of armour blocks, type of placing the armour units, number of layers, slope of the surface and nature of waves whether breaking
or non-breaking. Kd = around 2 to 4 for natural quarry rock, the lower
value for breaking waves, whereas, for tetrapods, that is being widely used
it is 7 and 8 for breaking and non-breaking waves, respectively. For other
artificial interlocking concrète blocks, like CoreLocs, accropods it is about
10 or even more. Refer CEM (2006) for more details.
8.3.2 Pressure distribution on an overtopped wall
Pressure distribution on an overtopped wall is brought out in Fig. 8.8. Wave
overtopping of vertical walls provides a réduction in the total force and
moment because the pressure above its crest will be absent. The effect of
overtopping should be considered in the design as this would exert seaward
pressure on the wall caused by saturated backfill or ponding water. The
total pressure is = yd + pi, as pi in the case of overtopping type vertical
wall can be established by incorporating the reflection coefficient and shown
in relation below.
Pi =
(8.8)
2
cosh 2kd
Coastal Engineering: Theory and Practice
Herein, fw is the friction factor and on assuming a long wave acts on
the armour, “u” can be u = constant, (gHb)1/2. Hence, the design massof
stone M can be calculated as,
___________ PsHb____________
FCp(ps/Pw - l)3(/^cosa - sina)3
The breaking wave height, Hb can be assumed to be the design wave
height, Kd as a constant that takes into account the characteristics of
the armor layer and ps and pw are the densities of armour layer for e.g.
rock and sea water, respectively. However, the formula of Hudson (1959) is
being widely adopted for obtaining the weight of the armour block which
is given as
w=_____11Kb. _____
(871
KD(Sr-l)3COte
where Hd is the design wave height in “m”,
is the unit weight of the
armour unit, 6 is the angle of revetment with the horizontal, submerged
weight of the armour, Sr = (Ps/Pw — 1)- Kd is a dimensionless stability
coefficient, determined through physical modelling. This value for Kd vary
for different kinds of armour blocks, type of placing the armour units, number of layers, slope of the surface and nature of waves whether breaking
or non-breaking. Kd = around 2 to 4 for natural quarry rock, the lower
value for breaking waves, whereas, for tetrapods, that is being widely used
it is 7 and 8 for breaking and non-breaking waves, respectively. For other
artificial interlocking concrète blocks, like CoreLocs, accropods it is about
10 or even more. Refer CEM (2006) for more details.
8.3.2 Pressure distribution on an overtopped wall
Pressure distribution on an overtopped wall is brought out in Fig. 8.8. Wave
overtopping of vertical walls provides a réduction in the total force and
moment because the pressure above its crest will be absent. The effect of
overtopping should be considered in the design as this would exert seaward
pressure on the wall caused by saturated backfill or ponding water. The
total pressure is = yd + pi, as pi in the case of overtopping type vertical
wall can be established by incorporating the reflection coefficient and shown
in relation below.
Pi =
(8.8)
2
cosh 2kd