Page 170 - Trenchless Technology Piping Installation and Inspection

136 Cha pte r F o u r

Some of the major causes of longitudinal bending or beam effect
are (Moser and Folkman, 2008):

• Differential settlement of manholes or other structures that
the pipe is connected to
• Nonuniform settlement or erosion of bedding
• Expansive soils
• Frost loading
• Nonuniform foundation
• Tree root growth pressure
Shear failure occurs in large-diameter rigid pipelines owing to
excessive shear stresses. Figure 4.14 illustrates an example of
shearing of bell joints in large-diameter (> 18 in.) cast-iron pipe.
Longitudinal tension may be caused due to temperature effects
or shrinkage of the embedment soil around the pipe (Moser and
Folkman, 2008).

FIGURE 4.14 Bell shearing in large-diameter cast-iron pipes. (Makar, 2001.)