Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 14—Repair and Abandonment of Conduitsembankment dam at several locations and injecting a thick sand and grout mix(sometimes referred to as compaction grout, limited mobility grout, or LMG) toform a bulkhead (Cadden, Bruce, and Traylor, 2000, p. 8). This technique wassuccessfully used to stop leakage in a deteriorating conduit through a 65-foot highembankment dam in southern Maryland (Traylor and Rehwoldt, 1999). In this case,the approximate location of the conduit was first established by use of severalgeophysical methods (magnetometer, resistivity, and self-potential). An experienceddriller can detect when the drill bit enters the existing conduit, advance it to themiddle of the conduit, and then pump the grout to form the bulkhead (Traylor andRehwoldt, 1999, p. 6). Grout was tremied into the existing conduit throughadditional holes drilled from the surface of the embankment dam.14.3.4 GroutingThe following paragraphs discuss the grout plan, mix design, and procedure:• Grouting plan.—A grouting plan detailing the contractor’s grout mix equipment,setup, procedures, sequencing, plan for handling waste, method forcommunication, and method for sealing and bulkheading upstream anddownstream should be submitted for review and approval prior to initiation ofgrouting operations.• Grout and concrete mixes.—Use a grout mix with a water (ASTM C 94) to cement(ASTM C 150) ratio of approximately 0.7:1 to 0.5:1. A grout fluidifier (ASTMC 937) may be needed to promote flowabilty, reduce water requirements,reduce bleeding, reduce segregation, increase strength, and eliminate groutshrinkage during setting of the grout mix. Trial mixes should be mixed at thejob site prior to grouting to confirm the expected performance of the mix. Forconcrete injection, ¾-inch aggregate should be used. A 28-day compressivestrength of 3,000 lb/in 2 is generally acceptable.• Procedure.—The pressure at the crown of the conduit as measured at the ventpipe should not exceed 5 lb/in 2 . Grouting is stopped when the air return pipein the crown flows full with grout. Cap the grout and air return pipes. Removethe bulkhead upon completion of grouting operations. For grouting orbackfilling of long existing conduits, the use of sections is recommended. Longgrout or backfill placements could result in sufficient expansion and/orcontraction to induce cracking of the existing conduit (concrete). The use ofsections is also conducive to ensuring an acceptable seal. Figures 199 and 200show grouting operations involved with the abandonment of an outlet worksconduit.361