Page 397 - Trenchless Technology Piping Installation and Inspection

Inspection and QA/QC for Trenchless Installation and Replacement Methods 347

times diameter of the product pipe. Furthermore, during the
final pullback, the pullback rate must not exceed 10 ft/min.
10. The pipe must be sealed at both ends with a cap or a plug to
prevent water, drilling fluids, and other foreign materials
from entering the pipe as it is being pulled back.
11. Pipe rollers, skates, or other protective devices must be used
to prevent damage to the pipe, eliminate ground drag, reduce
pulling force, and reduce the stress on the pipes and joints.
12. The drilling fluid in the annular region outside of the pipe
must not be removed after installation, and remain in place to
provide support for the pipe and neighboring soil.
13. If the drilling operation is unsuccessful, the contractor must
ensure to fill of any void(s) with flowable fill.
14. Entry penetration angles are limited by equipment capabili-
ties. However, according to most HDD drilling rigs’ design,
the best entry angle must be between 10° and 12°.
15. Exit angles generally range from 5° (for large-diameter steel
pipelines) to 12°. However, when high exit angles are encoun-
tered or designed, the pipe must be supported in an elevated
position during the pullback operation to prohibit the pipe
from bending, deforming, kinking, or even breaking.
Overcut Allowance
The overcut diameter must not exceed the outside diameter (OD) of
the pipe by more than 1.5 times diameter of the product pipe, to
ensure excessive voids are not created, resulting in postinstallation
settlements.
Watertight Joints
Watertight pipe joints are required to ensure the integrity of the road-
bed. Pipe must be constructed to prevent water leakage or earth infil-
tration throughout its entire length.
A watertight specification for each type of pipe material can be
obtained for each pipe material. Refer to the appropriate industry
specifications for more detailed information.
Drilling Fluids

1. Drilling fluid must be used during drilling and back-reaming
operations. Using water exclusively may cause a collapse of
the borehole while in unconsolidated soils, and may also
cause soil swelling while in clayey soils. Either case may
significantly impede the installation of the pipe.
2. Excess drilling fluids must be contained within a pit or con-
tainment pond, or trailer-mounted portable tanks, until
removed from the site.