Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 14—Repair and Abandonment of ConduitsIn the repair of voids along the outside of the conduit at Lake Tansi Dam (Heckeland Sowers, 1995), grout was placed through borings drilled from the top of theembankment dam using only the pressure from gravity (no pump). Holes with largegrout “takes” should be redrilled and grouted again to ensure that the voids are filled.The designer should strategically select the location of any additional holes tomaximize the filling of voids.In order to minimize the potential for accidentally filling the conduit with grout, anycracks or open joints in the conduit should be first repaired. For guidance on repairtechniques, see section 14.2.Any cracks or other defects should be plugged prior to grouting operations. Unlessconditions indicate otherwise, grout holes should be drilled and grouted in anappropriate pattern beginning at the downstream end of the conduit at the pipeinvert progressing up and around the pipe and from the downstream to the upstreamend of the conduit. Figure 191 shows the drilling of a grout hole from the interior ofan existing conduit.Grouting should progress so that grout is pushed in the direction of increasing waterpressures and up around the conduit to maximize grout penetration and filling ofvoids, and to minimize the potential for erosion of grout by flowing seepage waters.If suitably safe conditions exist, several rows of grout holes in advance of theFigure 191.—Drilling a grout hole from the interior of a conduit.347