Page 80 - Trenchless Technology Piping Installation and Inspection

50 Cha pte r T w o

For both gravity flow and internal pressure, design equations
have been categorized into partially and fully deteriorated on the
basis of ASTM F1216-09, as described in the following sections. See
Secs. 2.7 and 2.8 for sample design calculations and sample specifica-
tions, respectively.

Partially Deteriorated Pipe
A partially deteriorated existing pipe is defined as one where the
pipe is cracked or corroded, but has no missing pipe sections. The
soil-pipe system in this case is capable of supporting all the soil, and
surface loads. In this case, the new pipe is designed to support exter-
nal hydrostatic loads due to groundwater as well as withstand the
internal pressure in spanning across specific cracks and holes in the
original pipe wall.

Fully Deteriorated Pipe
In this condition, the existing pipe is not structurally sound and can-
not support soil and live loads or is expected to reach this condition
over the design life of the renewed pipe. This condition is evident
when sections of the original pipe are missing, the pipe has lost its
original shape (possibly collapsed), or the pipe has corroded or fail-
ing due to the effects of the fluid, atmosphere, soil, or applied loads.
The two basic design concepts are summarized in Table 2.2.
The specific design process for potable water pipelines (see Chap. 3)
will also include the following considerations:

• Internal corrosion: Lining must provide a highly effective,
corrosion-resistant barrier between the inside diameter (ID)
of the existing pipe and the conveyed product.
• Water quality problems associated with pipeline internal corrosion
and deposits: Lining must remove the pipe internal tubercula-
tion and corrosion which contributes to conveyed water-quality
problems.

Existing Pipe Conditions Design Objectives
Partially deteriorated Liner design guarantees long-term hole/
gap spanning capability under design
operating conditions. Structural support
is necessary from the existing pipe to
withstand general operating pressures/
external loads.
Fully deteriorated No structural support available from
existing pipe against internal/external
pressures/loads.
TABLE 2.2 Current Structural Design for Pipeline Renewal Systems