Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsMonitoring: The process of measuring, observing, or keeping track of somethingfor a specific period of time or at specified intervals.Mortar (ACI, 2000): A mixture of cement paste and fine aggregate. In freshconcrete, this is the material occupying the interstices among particles of coarseaggregate.Mud slab (ACI, 2000): A 2- to 6-inch layer of concrete below a structural concretefloor or footing over soft, wet soil; also called mud mat. Mud slabs are used toprotect foundations during construction.Multichannel Analysis of Surface Waves (MASW): An extension of SpectralAnalysis of Surface Waves, MASW uses multiple geophones (usually 24 or more) tosimultaneously acquire surface wave data on many points from a single seismicsource.Nondestructive testing (NDT): Geophysical methods for assessing the conditionof a conduit, embankment dam, or other structure, which do not require that aphysical sample be removed from the structure. These methods include seismictomography, electromagnetic tomography, ground penetrating radar, and ultrasonicpulse-echo. When combined with modern computer processing software, the dataobtained from the testing can be used to create detailed images of the structure.Nonpressurized flow: Open channel discharge at atmospheric pressure for part orall of the conduit length. This type of flow is also referred to as “free flow.”Normal water surface (FEMA, 2004): For a reservoir with a fixed overflow sill,this is the lowest crest level of that sill. For a reservoir whose outflow is controlledwholly or partly by moveable gates, siphons, or other means, it is the maximum levelto which water may rise under normal operating conditions, exclusive of anyprovision for flood surcharge.Nuclear gauge: An instrument used to measure the density and water content ofboth natural and compacted soil, rock, and concrete masses. The gauge obtainsdensity and water contents from measurements of gamma rays and neutrons that areemitted from the meter. Gamma rays are emitted from a probe inserted into themass being measured. Measurement of the gamma rays transmitted through themass, when calibrated properly, reflects the density of the mass. Neutrons areemitted from the base of the gauge. Measuring the return of reflected neutronswhen the gauge is calibrated properly can be related to the water content of themass.Offset (ACI, 2000): An abrupt change in alignment or dimension, eitherhorizontally or vertically.408