Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 14—Repair and Abandonment of ConduitsFigure 197.—Abandonment of a conduit by injection of cement groutthrough holes drilled from the surface of the embankment dam to depthsof up to 60 feet.constructed and is fully operational. The existing conduit is used for diversion whilethe new conduit is constructed.Any abandonment activities should also evaluate the need for partial or fulldemolition of the entrance and terminal structures, gate houses, plugging of gatechambers and shafts, and removal of certain mechanical equipment. Blasting fordemolition should not be permitted. Shaft structures can be backfilled withcompacted sand instead of concrete or grout.14.3.1 Drilling into the existing embankment damHistorically, drilling into an existing embankment dam has been performed for manyreasons. Some of these included the perceived need to extract samples forlaboratory sampling or to install instrumentation. However, as discussed in thefollowing paragraphs, drilling into an embankment dam can cause serious damage.The need to drill into an embankment dam should therefore be carefully considered.Many properties of the soils comprising an embankment dam can be reasonablyestimated from existing, published data, such as Reclamation’s Design of Small Dams(1987a). In other cases, general conditions within the embankment dam, such as thephreatic water level, can be reasonably estimated without the need to install apiezometer. Installing an instrument within the embankment dam to develop dataon a developing failure mode involving internal erosion or backward erosion piping357