Page 106 - Buried Pipe Design

82 Chapter Three

SF
W 3-edge 2592
BF
SF
W D load 2074
BF

Minimum Required Strength for SF 1.5
Bedding class Three-edge, lb/ft D load, (lb/ft)/ft
B 2046 1637
C 2592 2074
D 3535 2828

Choice may be based on job details including economic consideration of pipe
versus bedding cost. Choose a strength class that equals or exceeds strengths
given in the table above.

Example Problem 3.2 Suppose the trench width of 3.0 ft cannot be main-
tained at the top of the pipe in Example 3.1. What are the required
strengths if the transition trench width is reached?
1. Determine transition width.
H 14
11.20
B c 1.25

r sd p 0.5
From Fig. 2.6, B d /B c 2.9 and

15
B d
B d (transition) B c 2.9 3.6 ft
B c 12
2. Determine the earth load.
3.9
H
14

3.6
B d
K 0.192 granular
From Fig. 2.2, C d 2.0 and

2
2
W d C d B d 2.0 (120) (3.6) 3110 lb/ft
Alternately,

H 14
11.20
B c 1.25
r sd p 0.5