Page 54 - Buried Pipe Design

32 Chapter Two

S

L

y D D D SD
D t R R L 2

S y D

R b

D
R
b
t/D
Figure 2.17 Ring deflection due to axial bending.
Although Reissner’s derivation included internal pressure, it has been
omitted from Eq. (2.12) because the nonpressure case is the more crit-
ical for ring deflection (see Fig. 2.17). This type of bending frequently
occurs when pipes are bent around corners.

Differential settlement
Differential settlement of a manhole or other structure to which the
pipe is rigidly connected can induce not only high bending moments,
but also shearing forces. These forces and moments are set up when
the structure and/or the pipe moves laterally with respect to the
other. Quantitatively, these induced stresses are not easily evaluated.
Effort should be made during design and during construction to see
that differential settlement is eliminated or at least minimized. This
can be accomplished by the proper preparation and compaction of
foundation and bedding materials for both the structure and the con-
necting pipe.

Ground movement
Certain types of soils (mostly expansive clays) are influenced by mois-
ture content. Such soil may be subjected to seasonal rise and fall due
to changes in moisture. Good practice does not allow pipes to be