State of Technology Report for Force Main Rehabilitation, Final ...

thickness? It can still support the overburden soil and live loads, yet does not have an acceptable factor of
safety on pressure. According to the ASTM F1216 definition, this is a partially deteriorated pipe, while
most engineers might claim fully deteriorated based on its pressure capability.
The ASTM standards for new products coming into the market place designed to reconstruct pressurized
mains need to be modified to reflect a better understanding on what constitutes the various degrees of
deterioration that a pressurized main can undergo without failure. This will be important for sewer force
main renewal, as well as water main renewal.
5.2.2 Interactive vs. Independent. Liners for sewer force main renewal fall into two categories:
interactive or independent. Interactive liners are generally thin liners, in direct contact with the inside
wall of the existing pipe, and which have a much lower ring tensile stiffness than the existing pipe. When
pressurized, the existing pipe with the higher hoop stiffness will carry a proportionately higher percentage
of the tensile ring load. Consequently, interactive liners should not be used in sewer force mains where
the existing pipe has deteriorated to a point where it is not expected to be able to carry the full internal
pressure over the renewal design life. Examples of this might be a ferrous main that has suffered
extensive external corrosion with no protection, and has through-hole pitting over a significant portion of
the system. Placing a liner on the interior will arrest any internal corrosion and can be designed to bridge
over small holes and gaps, but will do nothing to stop any further external corrosion, which will
eventually lead to failure. In this case, the independent liner would be preferred.
An independent liner is one that is designed to carry the full internal working pressure and surge pressure
itself independent of any contribution from the host pipe. Slipliners are, by design, independent liners as
they are not in direct contact with the existing pipe (unless grouted in place) and will expand
circumferentially under pressure, but not transfer hoop load to the existing pipe. Some liner products start
off as interactive, as they will be close-fit, but have sufficient inherent strength to carry the full internal
pressure should the host pipe fail. These would then be considered independent liners.
The AWWA M28 Manual Rehabilitation of Water Mains has established four classes of design for
rehabilitation, ranging from non-structural to fully structural (AWWA, 2001). These definitions or
classes are more relevant to the design of sewer force mains than those found in the current ASTM
standards. The four classes are described below:
Non-Structural
• Class I – provides no structural support, only acts as an internal corrosion barrier and
improves water quality.
Semi-Structural
• Class II – resists external hydrostatic pressure from groundwater, bridges over holes and gaps
in the host pipe, but not able to carry the full internal pressure independently, adheres to the
interior surface of the host pipe.
• Class III – same as II except not dependent on adherence to the host pipe wall.
Full Structural
• Class IV – independently capable of resisting external hydrostatic pressure from
groundwater, and can handle the full internal pressure without support from the host pipe.
5.2.3 Design Loads. Depending on the state of deterioration of the existing main, the renewal liner
can be designed to be either a corrosion barrier or an outright pipe replacement. Some of the loads that
must be considered depend on the state of distress in the existing pipe, and include:
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