Page 384 - Trenchless Technology Piping Installation and Inspection

334 Cha pte r Ei g h t

9. The inside diameter (ID) of the casing pipe must be at least
6 in. larger than the largest outside diameter (OD) of the
carrier pipe to allow the carrier pipe to be inserted.
10. 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

Carrier Pipe
Carrier pipe material may be constructed with any material. The
carrier pipe diameter must be small enough to insert into the casing
pipe in conjunction with the casing spacers or wood blocking.

Casing Spacers
Casing spacers or wood blocking is required for all carrier pipes.
Casing spacers can be wood, plastic, fiberglass, stainless steel, or car-
bon steel. For gravity sewer installations, the void between the casing
and the carrier pipe must be filled utilizing the cellular grout, sand,
pea gravel, or other approved product.

8.4.3 Construction

Equipment
Equipment used for this method varies greatly. However, the basic
operations of boring, removing tailings, and jacking pipe are essential.
Please refer to the specific operator’s manual for more information.

Method
A full-size auger section must be used as the lead section of the casing.

Overcut Allowance
Overcut is the annular space between the excavated bore and the out-
side diameter of the casing pipe. The usual allowable overcut is 1 in.
greater than the casing pipe radius.

Watertight Joints
Steel casing joints are to be welded to prevent earth infiltration
through the joints and to withstand the required installation loads.