FLOOD06847

• County: Statewide
• Basin: Statewide
• Title: Bridge Scour and Stream Instability Countermeasures
• Date: 7/1/1997
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

1200
..
a. 1085 P.
Ii 100
II 945 Po
...
..
Ul
...
:I
.c
Ul
Gl
:s
;
oS!
CC

Allowable Tractive Force (Factor of Safety = 1.0)

80

I I I I I I I I I I I I
Articulated Concrete Block System
0
0
Block Size 1
Block Size 2
Rlprap Riprap 050 = 610 mm
- - - - . . Riprap 050 - 305 mm
Riprap 050 = 152 mm
0 . - -- -"
. -- -- -. '-
. -. --
- -- -- -. " f- ,.
-- --
0

600

400

20

o

10

20 30
Bed Slope, percent

40

50

Figure 4.4 Plot of allowable shear stress vs. bed slope

1.0
li
.: 0.9
0
tl
.. 0.8
IL
c
0 0.7
ts
::I
'0 0.6
Gl
a:
8- 0.5
0
in
Gl 0.4
'0
iii

I I-
, -Block Size 1
~ --- I-
-Block Size 2
............ --
K, = 0.73 --- - '--
K, 0.67
-

Side Slope Reduction Factors
1 V:5H 1 V:3H

lV:2.SH

lV:2H

0.3
o

10

40

50

20 30
Channel Side Slope, percent
Figure 4.5 Plot of side slope reduction factors

SteD 1: Determine the allowable shear stress for the hydraulic conditions.

From Figure 4.4 the allowable shear stress for the ACB's on a bed slope of 3.9% with a
factor of safety of one is:

ta = 945 Pa
ta = 1085 Pa

(allowable shear stress for Block Size 1)
(allowable shear stress for Block Size 2)

4.10