Page 279 - Trenchless Technology Piping Installation and Inspection

Pr oject Considerations for Pipe Replacement Methods 243

• Shaft length should be sufficient to allow alignment of the
bursting head with existing line and for the new pipe to bend
safely from the entry point to the ground surface.
• Space for the construction equipment, including backhoe,
loader, crane, and the like.
• Nearby flow bypass discharge location or space to lay bypass
lines without blocking driveways and intersecting roads.
• Traffic control around shafts.
• Soil borings close to proposed shafts.
• Discharge locations for dewatering, if necessary.
• Ability to use same shaft to insert or pull pipes more than
once.

In general, the engineer recommends locations for the insertion
and pulling shafts but leaves the final determination to the contractor
(through a submittal process), subject to minimizing excavation and
disturbance to the surrounding environment.

6.8.4 Geotechnical Investigation Requirements
The soil and subsurface investigations include collecting the neces-
sary technical information to properly design the project. It assists
the contractor in submitting a proper bid by selecting the appropri-
ate bursting system (type and size), shoring of the pulling and inser-
tion shafts, dewatering system, compacting backfill material, and
others, thereby increasing the chance of success during the con-
struction phase of the project. Thus, if the original soil borings
(during the existing pipe installation) are available, they should be
reviewed and provided as part of the supplemental information
available to the bidders. The determination of the trench geometry
and backfill material and compaction is important for the designer
and contractor.
The soil investigation activities comprise performing soil bor-
ings, standard penetration tests (SPT), groundwater level determina-
tions, trench geometry investigation, and native soil and trench
backfill material classifications. If the presence of washouts or voids
around the existing pipe is suspected, a ground penetrating radar
(GPR) survey may assist in determining the locations and magni-
tudes of these voids. Special attention should be given to the pres-
ence of obstacles that may render pipe bursting not feasible, such as
the presence of rock, hard cemented dense soils, very soft or loose
soils, reinforced concrete encasement, very narrow trench in hard
soils or rock, or ductile iron point repairs. If contaminated soil is sus-
pected, the type and extent of contamination should be identified
and indicated in the contract documents. The contractor should be