Page 158 - Buried Pipe Design

132 Chapter Three

X D H Z
X D H Z

D
X

H Z
Figure 3.29 Cover term X/D as a function of the soil strength term H/Z for a ver-
tical trench wall excavated parallel to a very flexible pipe.

deflection would have to be included. Then the coefficient of friction
between pipe and soil should also be included as a fundamental
variable.
If the pipe has significant ring stiffness, the height of soil cover that
it can support without collapse can be found for uniform vertical pres-
sure with no side support.

Pr 2 Mc
Moment M Stress
4 I

For pipes, at yield stress, based on elastic theory,
4
y I 16
I
P y y (3.29)
r 2 c D 2 c
where P vertical soil pressure
I moment of inertia of wall cross-section
D pipe diameter 2r
c distance to wall surface from neutral surface t/2 for plain
pipes
t wall thickness of plain pipes