Page 368 - Trenchless Technology Piping Installation and Inspection

318 Cha pte r Ei g h t

Allowable Forces
The allowable jacking strength capacity of pipe must be capable of
withstanding the maximum jacking forces imposed by the operation.
The specified allowable jacking capacity of the pipe must be 2 times
greater than the maximum jacking forces imposed by jacking opera-
tions as identified by theoretical calculations.
Pipe Requirements

1. The pipe diameters used for microtunneling method is
dependent on the size of the microtunnel boring machine.
The minimum size of the microtunnel machine is 12 in., and
the maximum size is limited by the maximum size of pipe
suitable for pipe jacking.
2. There are certain provisions for pipe thickness (or DR) based
on the pipe material. For example, steel pipe may need to
have a minimum wall thickness of 0.25 in. or as specified in
the approved standard specifications for construction.
3. Pipe must be round. Steel pipe must have a roundness tolerance,
so that the difference between the major and minor outside diam-
eters must not exceed 1 percent of the specified nominal outside
diameter, or 0.25 in., whichever is less. Likewise, concrete and
other types of pipes must have similar roundness tolerances.
4. Pipe must have square and machine-beveled ends. The pipe
end maximum out-of-square tolerance must be 0.04 in.
(measured across the diameter).
5. Pipe must be straight. The maximum allowable straightness
deviation over any 10-ft length of steel pipe is 0.125 in.
6. Pipe must be without any significant dimensional or surface
deformities. All pipes must be free of visible cracks, holes, for-
eign material, foreign inclusions, blisters, or other deleterious
or injurious faults or defects. Any section of the pipe with a
gash, blister, abrasion, nick, scar, or other deleterious fault
greater in depth than 10 percent of the wall thickness, must
not be used and must be immediately removed from the site.
7. Any of the following defects warrants pipe rejection:
• Concentrated ridges, discoloration, excessive spot rough-
ness, and pitting
• Insufficient or variable wall thickness
• Pipe damage from bending, crushing, stretching, or other
stress
• Pipe damage that impacts the pipe strength, the intended
use, the internal diameter of the pipe, and internal rough-
ness characteristics
• Any other defect of manufacturing or handling