Page 277 - Trenchless Technology Piping Installation and Inspection

Pr oject Considerations for Pipe Replacement Methods 241

pipes can be burst. Pipe bursting is commonly performed size-for-
size and one-size upsize above the diameter of the existing pipe.
Larger upsize (up to three pipe sizes) have been successful, but the
larger the pipe upsizing, the more energy is required and greater
ground movement will be experienced. It is important to pay close
attention to the project surroundings, depth of installation, and soil
conditions when replacing an existing pipe, especially in unfavorable
conditions such as expansive soils, pipe repairs made with ductile
material, collapsed pipe, concrete encasement, sleeves, and adjacent
utility lines.
Pipe bursting has the following specific limitations:
• Insertion and pulling shafts are required, especially for larger
bursts.
• Excavation for service lateral connections is required.
• Expansive soils may cause difficulties.
• A collapsed (existing) pipe segment may require excavation
at that point to allow the insertion of pulling cable or rod and
to repair pipe sag.
• Point repairs with ductile material can interfere with the
bursting and replacement process.
• If the existing sewer line is significantly out of line and grade,
the new line will also tend to be out of line and grade, although
some corrections of localized sags are possible.

6.8 Design Considerations
The design phase starts with collecting information regarding the
existing pipe, including current flow volume for bypass pumping,
lateral connections, trench width, backfill compaction levels, and
manhole locations. This phase also includes locating nearby utilities,
investigating soil and trench backfill material, and developing risk
assessment plans. The designer completes this phase with the devel-
opment of detailed drawings and specifications and complete (final)
bid documents which include a listing of required submittals. The
drawings should provide all relevant information concerning the
existing pipeline and environment, such as diameter and material,
plan view and profile, nearby utilities and structures (crossing and
parallel), repair clamps, concrete encasement, fittings, and the like.
Some of this information may be collected by means of a closed
circuit television (CCTV) system or equivalent.

6.8.1 Utility Survey
The presence and nature of surrounding utilities will have a signifi-
cant impact on the success of the pipe-bursting operation, and the