# COFFERDAM DESIGN COMPUTATION

```Design Computation for Cofferdam
TOP OF SHEET FILE
Properties of Type II Sheet Pile ( L = 12m.)
S
S.Y
IX
wt.
= 874cm&sup3;/m (12m. ) = 10.488x10-3m3
= 295MPa
= 152.9 cm&sup2;/m
= 48kg/m.
CRANEWAY
H2O
w
=1000kg/m&sup3;
w = 400mm.
h = 400mm.
t = 10.5mm.
P1
WATER LEVEL
SAND
RIVER BED
s=
1600kg/m&sup3;
TOP OF PILE CAP
P2
P3
BOT. OF PILE CAP
0
Moment center
DESIGN COMPUTATIONS
P1 = Water Pressure
P2 = Soil Pressure Rectangular
P3 = Soil Pressure Triangular
let h = 5 m.
w = 1000kg/m&sup3;
= 9,810 N/m&sup3; ( Mass density of Water )
P1
= 9,810 N/m&sup3; x 5.0m. ( 5x0.4)
= 98,100 N / 2
= 49,050 N
P2
= 9,810 x 4.10 ( 4.10 x 0.4 )
= 65,962 N
P3
= 1,600 kg x 9.81x 4.10 ( 4.1x0.4 )
= 105,539.9N / 2
= 52,769.95 N
ƩM0 = P1h1 + P2h2 + P3H3
h1
h2
h3
= 4.1 + 5 3 = 5.767m.
= 4.12
= 2.05m.
4.1
=
=1.367m.
3
ƩM0 = 49.050 (5.767) + 65,962.44(2.05) + 52,770(1.367)
= 490,229.97 N.m
ƒ
= MS
= x 490,230 N.m 10.488 x10-&sup3;m&sup3;
ƒ
= 46,741,988 N/m2 &lt; 295MPa Ok Safe
Safety Factor
= 6.31
Design Computation for Cofferdam
Design for Waler and Strut :
A.
6.5 m.
w = 73,575 N/m.
WALER (Above River Bed)
(SI)
(US)
Using W250 x 80 : W10x54
wt.
= 80.1kg/m.
Sx
= 982 x10&sup3;mm&sup3;
= 982 x10-6m3
A
= 10,194mm2
Fy
= 437MPa
R1 = 239,118.8 N.
Spacing of Waler = 1.5m O.C.
Spacing of Strut = 6.5m O.C.
R2= 239,118.8 N.
3.25m.
3.25m.
Max. M= 388,568 N.m.
Computation for w:
w
ƒ
= (9,810 N/m3) (5m.) ( 1.5m.)
= 73,575 N/m.
=M
S
=388,568 N.m.
982x10&macr;⁶m&sup3;
ƒ
= 395.7 MPa &lt; 437 MPa Ok Safe
B.
STRUT (Above River Bed)
Satety Factor =1.104
Force resisted by Strut
P1
= [ 1,600 kg/m3 x 9,810 N x 4.10m.] [1.5m x 6.5m. ]
1kg
= 627,448N
ƒc
= Pc = 627,448 N.
ƒc
= 61.55PMa &lt; 437MPa Ok Safe
Ac
10,194mm&sup2;
Safety Factor = 7.1
Design Computation for Cofferdam
A. Waler (Below River Bed)
w
= (9,810 N/m&sup3;) (4.10m) ( 1.5m) + (1600kg/m&sup3;)(9,810N/kg)(4.10m.)(1.5m)
= 60,331.5 + 96,530.4
= 156,862 N/m
Using W360 x 162 = W14x109
wt.
= 162kg/m.
Sx
= 2,835 x10&sup3;mm&sup3;
= 2,835 x 10-6m3
Fy (Yield Strength) = 404MPa
ƒy
6.5 m.
w = 156,862 N/m.
R1 = 509,801.2 N.
=M
S
= 828,427 N.m.
R2 = 509,801.2 N.
3.25m.
3.25m.
2,835x10⁶m&sup3;
= 292,214,077.4 N/m2
= 292.2 MPa &lt; 404MPa Ok Safe
Safety Factor = 1.383
B. Strut (No Strut below Pile cap
Max. M= 828.426.91 N.m.
```