Technical Manual: Conduits through Embankment Dams (FEMA 484)

Contents81 On first filling, a high hydraulic gradient exists in the embankment dam as a wetting front moves through the dam. The wetting front will not besmooth. Projections will exist due to the different permeability of theembankment dam. The water pressure pushing against the soil can easily be greater than the lateral stress, and hydraulic fracture can result ........ 11782 The failure of this embankment dam located in South Carolina was attributed to hydraulic fracture. The eroded seam located to the right of the conduit may have been the hydraulic fracture that formed and allowedinternal erosion and failure of the embankment dam. The embankment was composed of dispersive clays ..................................11783 Recommended earthfill ramp and conduit side slopes .................. 12384 An embankment dam in Mississippi constructed of dispersive clay soil, failed on first filling with low reservoir level. Failure was likely caused by cracks from differential settlement, hydraulic fracture, or poor compactionabout the outlet works conduit. This embankment dam had no filter ..... 12585 This embankment dam constructed with dispersive clays failed on first filling of the dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................12586 Illustration of the mechanism of development of a filter seal resulting from the accumulation of eroding soil particles at the face of a designed filter zone, showing filter cake development (top), and sealing of concentrated leak (bottom). The filter seal results in a thin zone of soil with a slurry-like consistency and a permeability similar to that of the soils that eroded to form the seal................................... 13287 Two stage chimney filter within an embankment dam located in Texas . . . . 13588 Typical configurations for chimney filters used in the design of embankments with conduit penetration. A chimney filter may be constructed either on a slope (top) or with a vertical configuration (bottom) within the embankment dam ..............................13689 Typical design used for embankment dams with distinctly differentmaterials in the core zone and exterior shells of the dam................ 13790 Construction of a filter diaphragm within an embankment dam .......... 13991 Typical configuration for filter diaphragm used in the design of an embankment dam ...............................................13992 Typical configuration for filter diaphragm used in design of an embankment dam. The filter diaphragm should extend into the foundationsoils, where an excavation is made for the conduit..................... 14293 Typical configuration for a filter diaphragm used in the design of anembankment dam. The figure shows the location of the filter diaphragm as far downstream as possible, leaving adequate cover over it ............ 14494 Filter collar surrounding a conduit renovation ........................14695 Cross section showing a filter collar surrounding a conduit renovation. The drain pipes located on both sides of the conduit collect and convey any seepage within the filter collar to a downstream exit location ......... 146xix