The first question the designer needs to ask is whether the conduit should be replaced or is a good candidate for rehabilitation. Conduit replacement is likely the approach providing the greatest reliability, but that approach will most likely require draining of the reservoir and be the highest cost option. In some cases, rehabilitation provides a reasonable alternative.
From Low-Level Conduits - Rehab or Replace?, Western Dam Engineering 2013 🔗
Advantages vs. Disadvantages of Rehabilitation (CIPP, Slipline)
- Limited or no excavation required.
- Installation during weather conditions not suitable for replacement.
- It may be possible to maintain a full reservoir in some cases.
- Shortened construction schedule and reduced cost when compared to replacement.
- Not applicable for severely deteriorated conduits.
- Limitations for conduits with slight bends, deformities, or conduits believed to have voids along the outside of the conduit.
- Most likely will require specialized contractors and equipment for installation.
- May adversely affect seepage paths around the exterior of the conduit.
Advantages vs. Disadvantages of Replacement (Open Cut)
- Visual embankment/foundation evaluation after conduit removal.
- Allows repair of surrounding embankment that may have been damaged because of deteriorated condition of existing conduit.
- Allows for easy incorporation of filters designed according to the current state-of-practice.
- Potential for increasing the hydraulic capacity of the conduit.
- Conduit Replacement does not require specialty contractors, equipment or personnel.
- Unless the reservoir can be drained, the construction of a cofferdam is generally required. Inflows into the reservoir will need to be diverted. In some special cases a downstream cofferdam may also be required.
- Construction costs for removal and replacement are generally higher than for other renovation methods. Construction costs rapidly rise as the height of the embankment dam increases.
- Construction may impact reservoir operations and add risk to the downstream community.
- If proper compaction of the embankment closure section is not obtained, potential seepage paths may exist along the junction of the closure section and existing embankment.
From Conduits Through Embankment Dams, FEMA 2005 🔗 (Pg. 289)
Low-Level Conduits - Rehab or Replace?
Publication: Western Dam Engineering
Date Published: 2013