Page 75 - Trenchless Technology Piping Installation and Inspection

CHAPTER 2

Existing Pipeline Renewal

and Replacement Methods

2.1 Introduction
Trenchless renewal and replacement methods can be used to renew
both gravity and pressure pipelines. Range of applications include
sanitary sewers, storm sewers, culverts and drainage structures, pota-
ble water pipes, natural gas and oil pipelines, sewer manhole struc-
tures, and so on. Each method has certain capabilities and limitations
that make them more suitable for specific applications and specific
conditions. The decision process to select a specific method should
consider many factors, including nature and extent of existing pipe-
line deterioration and problems, type of application, pipe geometry
(see Fig. 2.1), as well as plans for future pipe applications, costs and
availability of contractors and technology providers. Although numer-
ous cross-sectional shapes are available, the circular shape is the most
common shape for a pipe because it is hydraulically and structurally
efficient under most conditions. A pipe-renewal selection should also
consider construction cost, potential for clogging by debris, limita-
tions on headwater elevation, pipe depth, and hydraulic performance
of the new pipe. The site (soil conditions, surface conditions, and
availability of space for installation), and project-specific conditions
(length of pipe, bends, alignment conditions, bypassing requirements,
future and current land use, and so on) would also influence selection
of a specific method.
2.1.1 Existing Pipe Underperformance
There are a wide variety of factors that affect performance of
existing pipes. Among these factors, structural loads (soil and live
loads), corrosion, excessive fluid pressure, inadequate flow capac-
ity, scour, and erosion of streambed and embankments are most
common. Existing pipe performance is closely related to the rate of
deterioration and the service life. Noninspected and nonmaintained
pipes deteriorate faster than expected due to various service,

45