Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 12—Renovation of Conduitsworks conduit (150 feet in length) is to be sliplined, 4 grout pipes (120, 90,60 and 30 feet in length) would be needed to grout the annulus.Bulkheads are placed around the annulus of the slipliner at both ends ofthe conduit to contain the grout. The bulkheads must be secured in placeand sealed, so no leakage of grout will occur during grouting operations.Air vent bleeder systems are installed through the bulkheads, near thecrown of the existing conduit at both ends of the conduit to prevent airand bleed water from being trapped within the annular space.Injection of grout into the annular space starts at the downstream end ofthe HDPE slipliner and progresses upstream through the longest groutpipe first, while low pressure air (5 lb/in 2 ) is pumped through thedownstream air vent. The air pressure assists in holding the grout in theannulus space. Grout pressures should be kept as low as possible to avoidcollapsing the HDPE slipliner. As grouting begins, the upstream air ventthrough the bulkhead remains open until grout begins to flow from thevent, and then the vent is closed.Grouting continues in the longest pipe until no air returns from the nextlongest pipe, or grout no longer flows through the longest pipe. Thelongest pipe is plugged and grouting is initiated on the next longest groutpipe and the sequence is repeated for this pipe. Pumping of air in the airvent is discontinued when the shortest grout pipe on the conduit is beinggrouted. Grouting of the last grout pipe is continued until the annularspace is fully grouted. When the annular space is fully grouted and heavygrout returns from the downstream air vent, a grout pressure of 10 lb/in 2is maintained for 10 minutes to ensure all voids are filled.Postinspection and acceptance.—The completed HDPE slipliner (figure 176)should be visually inspected by trained personnel to evaluate the conditions withinthe renovated conduit. If the sliplined conduit is too small for man-entry inspection,CCTV inspection methods should be used. Some designers may want to considerthe use of white or gray HDPE pipe to reduce glare using CCTV equipment, figure177 shows an example of this type of pipe. See section 9.5.2 for guidance oninspection of conduits. No localized dimpling or distortion of the HDPE sliplinerwall or infiltration of groundwater or grout should be present.Maintenance and repair of the completed HDPE slipliner.—No maintenance istypically required for the HDPE sliplined conduit, unless the conduit requires sometype of cleaning. Periodic operation of the conduit usually is sufficient to flushsediments through the system. HDPE pipe is smooth and generally resists theadherence of sediment deposits. See section 9.6 for guidance on cleaning ofconduits.311