Page 129 - Buried Pipe Design

104 Chapter Three

Through transposition, Eq. (3.8) can be restated as

y
R s
(3.9)
D AR s B
In this form, the above equation represents a simple relationship
between two dimensionless variables: ring deflection ratio y/(D ) and
stiffness ratio, R s . Figure 3.18 represents the design curve that can be
used for predicting ring deflection. It is based on current theoretical as
well as empirical data generated in Europe and the United States.
In most flexible pipe installations, the pipes are relatively flexible
compared to recommended sidefill. Thus, the pipe follows the soil
down, and the deflection ratio approaches unity. The stiffness ratio R s
is usually greater than 300, which is to the right of the plot of Fig. 3.18.
Even if R s is usually greater than 300, it is conservative to assume
( y/D)/ 1. So the ring deflection becomes

y
(3.10)
D

Dimensionless

D
Δy Œ P v H
Ring Deflection Factor Œ ΔH H El D H

E s
R s
3
E s P v
Œ
3
El D
Stiffness Ratio R s , Dimensionless
Figure 3.18 Ring deflection factor as a function of stiffness ratio.