Conduit / Pipe Rehabilitation

Rehabilitation is typically accomplished by one of three methods, sliplining solid pipe, installing cured-in-place pipe (CIPP) liners, or using internal sleeves. Any time you change the equilibrium of a pipe by adding internal lining, there is risk that seepage will begin to move along the outside of the pipe. Thus, seepage control must also be considered.

Slipline Solid Pipe

Sliplining is completed by installing a smaller, "carrier pipe" into a larger "host pipe", grouting the annular space between the two pipes, and sealing the ends. The carrier pipe is commonly made of steel or plastic.

• Slipline Example 1
• Slipline Example 2

Slipline Cautions:

• ⚠ May force water along outside of pipe
• ⚠ May require more grout than anticipated

References
Cellular Grout Use in Conduit Sliplining

Cured-in-place pipe (CIPP)

What is CIPP? Cured-in-place pipe (CIPP) is a common method used to rehabilitate outlet conduits in dams. The CIPP system consists of a flexible fabric tube and a resin system that is hardened by a curing method. CIPP is installed inside an existing pipeline by either an inverstion method or a pulled-in-place method. After the CIPP is installed, it is cured in place using one of several available techniques and forms to the shape of the existing pipe, including minor irregularities.

• CIPP Works well for Smaller Conduits
• ⚠ Cautions for CIPP in Large Diameter Conduit

CIPP Examples:

• CIPP Example 1
• CIPP Example 2

Advantages of CIPP:

• CIPP is corrosion resistant and is not affected by naturally occurring soil and water conditions. It may be preferable in certain conduit applications where aggressive water or soil chemistry would limit the life of concrete or metal pipe.
• The smooth interior surface reduces friction loss. Also, due to the very smooth surface of pipe, adherence of minerals (e.g., calcium carbonate) is minimized.
• Thermoset plastic pipe resists biological attack
• Typically, the need for grouting of the annulus between the CIPP liner and existing conduit is eliminated, since it is tight fitting

Disadvantages of CIPP:

• High material and installation costs.
• Not suited for conduits with significant bends or changes in diameter.
• Inability to accommodate internal and external loadings when the original conduit is severely damaged.

References
You Down with CIPP? – Yeah! You Know Me!

Internal Sleeve

What is an internal sleeve? Internal pipe sleeves are used for in-place rehabilitation. Typically, a rubber sleeve is applied over the damaged area of the inner wall of the pipe. The sleeve is then held in place by stainless steel retaining bands. Installation time can be as little as 40 minutes per sleeve and provides a noncorrosive, bottle-tight connection around the full inside circumference of the pipe.

• Internal Repair of Isolated Damage (Joint)

References
Mechanical Seals for Conduit Repair

Seepage Control

A filter diaphragm is a designed zone of filter material (usually well-graded, clean sand) constructed around a conduit. It is a standard defensive design measure to prevent problems associated with seepage or internal erosion in earthfill surrounding a conduit. The purpose of a filter diaphragm is designed to intercept water that can flow through cracks that may occur in compacted fill surrounding conduits or water that may flow along the interface between the conduit and the surrounding fill.

Filter Diaphrams are Important Protection from Erosion Along Pipe

• Filter Diaphragm Exhibits

Downstream Pipe Treatment

• Filter Diaphragm may Require Downstream Pipe Replacement or Extension

Note: The content on this page was originally created as part of DamOutletWorks.org (DOWL, 2018). It has subsequently been updated and reformatted as part of the Dam Safety Toolbox.
Revision ID: 6868
Revision Date: 06/19/2023