EM 1110-2-1100 (Part V)
31 Jul 2003
EXAMPLE PROBLEM V-4-7
FIND:
The "half-life" of the specified beach fills (time at which 50 percent of the beach-fill material
remains within the placement area).
GIVEN:
Both projects have a rectangular planform and differ only in alongshore length. Beach fill A
has an alongshore length of 3 km, whereas beach fill B has an alongshore length of 6 km. Both projects
are subjected to the same wave environment.
ρs/ρ = 2.65
Assume:
K = 0.77
Hb = 0.95 m
n = 0.4
Cgb = (g hb)1/2
db = 2.5 m
hb = Hb/0.78
dc = 6.0 m
g = 9.81 m/s2
SOLUTION:
Equation III-2-26 gives
0.77 (0.95)2.5 9.81/0.78
m2
1
1
1
ε'
.
.
.
' 0.03568
8
(2.65 & 1) (1 & 0.4) (2.5 % 6.0)
sec
Solving Equation V-4-12 for t and p(t) = 0.5 gives
a2 π
t50%
'
4ε
Half-life of beach fill A
(1500)2 (3.14)
' 49.526 X 106 sec 1.57 years
t50%
'
(4) (0.03568)
Half-life of beach fill B
(3000)2 (3.14)
' 198.102 X 106 sec 6.28 years
t50%
'
(4) (0.03568)
Beach Fill Design
V-4-51
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