Technical Manual: Conduits through Embankment Dams (FEMA 484)

Conduits through Embankment DamsProject name: Beltzville DamLocation: PennsylvaniaSummary: Conduit crack surveyBeltzville Dam is located in northeastern Pennsylvania. The embankment dam has astructural height of 170 feet, a crest length of 4,560 feet, and a crest width of 30 feet.Appurtenant features include a spillway and an outlet works. The outlet works isused for flood control. The outlet works consists of a gated intake structure, a7-foot diameter concrete conduit approximately 1,165 feet in length, and a stillingbasin. The USACE with assistance from the Beltzville Lake operations personnelperformed a condition survey (also called a crack survey) of the outlet works conduitin July 2003. Previous formal surveys had taken place in 1971, 1988, 1992, and 1999.Although not specifically meeting all of the parameters defining a confined space, theoutlet conduit was treated as such for man-entry. Personnel were trained in confinedspace operations and air monitoring equipment, and a hard-wire communicationstool was used during the survey. Drawings showing that the results of the previoussurveys were used as a baseline for performing the current mapping. Stationingwithin the conduit is marked periodically on the conduit walls, although somemarkings have lessened in intensity. Digital photographs were taken of some of themore prominent features.Spalling had occurred at joints and other localized spots. Minor cracking, spalling,surface abrasion, and calcitic efflorescence were observed and mapped. Figures B-20through B-23 are typical of these features. No major leakage was evident; however,minor seepage of water was observed in two locations but with no material beingcarried.The 2003 survey noted changes in the sizes of some of the spalls and sevenadditional (or not-previously-mapped) spalls. Two new (or not-previously-mapped)occurrences of cracking and three new (or not-previously-mapped) occurrences ofcalcitic efflorescence were observed. Conversely, calcitic efflorescence no longerexisted in six locations where it had been previously mapped. Flow through theconduit during high releases appeared to have removed these materials. In general,the condition of the conduit had changed little from the 1999 survey. A comparisonof photos taken in 1999 and 2003 also indicated little change in the more prominentfeatures. Drawings showing the features are developed after each survey iscompleted using different colors to denote the different surveys in order to followchanges in condition of the conduit.B-22