Rehabilitation of Wastewater Collection and Water Distribution ...

Capacity
10%
3rd party
damage
Internal
corrosion
27%
Joint
Leakage
3%
3rd Party
Damage
36%
19% Surge
Pressure
7%
External
Corrosion
Joint
leakage
15%
Surge
pressure
10%
corrosion
19%
Structural
27%
27%
(a) Ferrous Force Mains (b) Nonferrous Force Mains
Figure 2. Main Causes of Failure in Ferrous and Non-ferrous Force Mains
and coating of interior walls are the typical approaches for such rehabilitation. Since the shape of the
structures is often rectangular, it is not possible for liners to resist external groundwater pressure by
arching action in curved sections; hence, most coating applications require the ability to bond to the
existing structure. Further complicating the ability to seal such structures fully are the internal supports
for equipment that may be bolted to internal walls and penetrations for venting to pass through the walls
of the structure and any waterproofing or sealing layers. Providing a structure that is easy to maintain and
keep dry is easiest during the initial design by:
• Keeping external and internal shapes as simple as possible for ease of construction and
waterproofing.
• Avoiding sharp, re-entrant corners wherever waterproofing or sealing layers are to be
applied.
• Ensuring that internal supporting members preferably slope slightly towards the wall of
the structure so that leakage water will be kept adjacent to the wall. The same applies to
the floor-to-wall junction.
• Providing an internal drain at the floor-wall junction for confining leakage issues and
allowing easy collection and disposal of leakage.
• Carrying out an analysis of pump operations, maintenance, and emergency procedures
during the design so that the facility can operate effectively and avoid damage to adjacent
pipe sections.
Wet well areas of lift and pump stations are subject to erosion and corrosion concerns, depending on the
structural materials used and the level of hydrogen sulfide produced by turbulence in the wastewater flow.
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