Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment Dams14.3.3 PreparationsThe existing conduit surfaces against which grout will be placed should be free ofroots, sediments, mineral deposits, dust, latence, loose or defective concrete, curingcompound, coatings, and other foreign materials. See section 9.6 for guidance oncleaning conduits. Any sediments or debris should be removed from the invert ofthe existing conduit. Any bolts or other projections should be cut off flush and/orground smooth with the interior surface of the existing conduit.If water is entering the existing conduit and cannot be stopped, an inflatable bladdermay be required. The pressure required to inflate the bladder and seal off inflowmust be closely evaluated to avoid rupturing the conduit. This is usually a concernwhen high head is present in the reservoir. Also, some pipe materials, such ascorroding CMP, are more susceptible to rupture. Abandonment of the existingconduit may need to be scheduled to allow grouting operations when the reservoir isat its lowest annual elevation. Siphons or pumps can be used to further reducereservoir elevations. In some cases, the construction of a cofferdam may be moreapplicable, if the reservoir water level needs to remain at a constant elevation. If anew conduit is being constructed, grouting of the existing conduit can be delayeduntil the new conduit can be used for diversion.For accessible existing conduits, any open or leaking joints or holes should bepatched to minimize grout leakage. A bulkhead should be installed at thedownstream end of the existing conduit to resist the loadings from the grout orconcrete. An air return (vent) pipe or a series of pipes should be installed at thecrown of the conduit and extend from the upstream end of the conduit to thebulkhead.Grout pipes should be installed at the crown of the conduit. The longest pipesshould be attached directly to the crown and the other pipes as closely to the crownas possible. Vent pipes can be used as grout pipes after grout return occurs. Groutpipes typically are Schedule 40 PVC, HDPE, or electrical mechanical tubing.Generally, grout pipes less than 100 feet in length can be ¾ inch diameter. Groutpipes longer than 100 feet should be 1½-inch diameter. The grout and vent pipesinstalled at the crown should be water tested.Grouting equipment should be capable of continuously pumping grout at anypressure up to 50 lb/in 2 . Injection pipes for concrete should be about 5 inches indiameter.The abandoning of an inaccessible existing conduit is much more problematic due tothe lack of access into the interior of the conduit. Stopping the flow of water intothe existing conduit may be difficult, if there is an opening through the conduit.Abandonment may be possible by drilling into the conduit from the surface of the360