Page 28 - Trenchless Technology Piping Installation and Inspection

New Pipeline Installations 3

modified Iowa formula was published (Watkins and Spangler, 1955).
The Iowa formula is not a basis for design of pipe, but rather it pre-
dicts ring deflection of flexible pipe when buried and shows the
importance of the soil embedment. Spangler is considered as “the
father of pipe-soil interaction.”

1.2 Open-Cut Method of Pipe Installation
The conventional method for construction, replacement, and renewal
of underground utilities has been trenching or open cut (OC), an indi-
rect method of pipeline installation. Open-cut methods involve digging
a trench along the alignment of the proposed pipeline, supporting
trench walls (or sloping sides of trench), constructing bedding or
foundation, placing the pipe sections in the trench, embedding the
pipe sections, and backfilling the trench and compacting operations
(see Fig. 1.1). In open-cut construction, the construction effort is con-
centrated on such activities as managing the traffic flow through
detour roads, trench excavation and shoring, shielding or sloping,
dewatering (if needed), backfilling and compaction operations, and
reinstatement of the surface. This leads to a small part of the construc-
tion effort actually being focused on the final product, which is the
pipe installation itself. In some cases, the double handling of the soil,
including trenching, stockpiling, hauling, backfilling, compacting, and
reinstating of the ground and pavement alone may amount to 70 percent
of the total cost of the project.
Additionally, open-cut methods include higher “social costs.”
Social costs include costs to general public (such as traffic disrup-
tions, noise, and dust), negative impacts to the environment (higher

Backfill
In situ
soil
Embedment
(Height varies)
Trench
walls

Haunch
area Bedding

Foundation
FIGURE 1.1 Open-cut installation. (Howard, 2002.)