Technical Manual: Conduits through Embankment Dams (FEMA 484)

Appendix B—Case HistoriesFigure B-74.—A sinkhole occurred above the monolithjoint at the junction of the intake tower and theupstream end of the transition section.with a jack hammer to a depth of about 2 feet, and (2) a 1½-inch pipe with a ballvalve on the upper end was then grouted into the hole. After the grout had set up, ajack hammer with bit small enough to go inside the 1½-inch pipe was used to drillthe rest of the way through the conduit to the foundation or backfill material. Whenfoundation or backfill material was encountered, the holes would start to flow. Thejack hammer with bit was then removed, and the ball valve was closed to prevent thehole from flowing. A water jet pipe was used to clean out the grout pipe just prior togrouting. At the end of the grouting operation, the ball valves were removed, andcaps were placed on the grout pipes.The first hole grouted took 12 cubic feet, and the take per hole decreased for eachsucceeding hole. A total of 40.5 cubic feet of neat cement grout was pumped aroundthe joint.The cement grout was anticipated to be brittle, and there was some concern that anyadditional settlement of the foundation could cause this neat cement to crack.However, this repair was completed more than 30 years ago and no other sink holeshave developed.B-99