Dam within a Dam

by Tarek F. Haider, P.E., Sr. Geotech. Engr.; Gannett Fleming, Inc., Valley Forge, PA,
Michael J. Byle, P.E., Geotch. Dept. Mgr.; Gannett Fleming, Inc., Valley Forge, PA,
Richard E. Horvath, P.E., Proj. Mgr.; Gannett Fleming, Inc., Valley Forge, PA,

Serial Information: Civil Engineering—ASCE, 2001, Vol. 71, Issue 11, Pg. 56-61

Document Type: Feature article


A routine inspection of the Rock Run Dam, an 84-year-old Ambursen-type structure in Chester County, Pennsylvania, revealed major stress cracks and water stains on the inside face of the bay at the east end. The facility provides one of only two water sources for the 13,000 residents of the city of Coatesville, so to prevent its total failure, engineers determined that a stabilization of the bay while the dam remained in service was necessary. Few as-built drawings were available for the dam, so the designers decided that no new loadings should be imposed on the existing structures. With limited space for construction, the design team decided to fill the interior of the east-end chamber with mass concrete to suport the upstream face. The engineers analyzed several methods of supporting the mass concrete infilling, including a shallow foundation on stabilized soil, a shallow foundation extending through the overburden soil, and a deep foundation. Ultimately, the presence of a competent bedrock stratum 30 ft (9m) below the surface made a deep foundation that would not be hampered by the limited headroom in the bay, drilled pipe piles proved to be the best choice.

Subject Headings: Shallow foundations | Mass concrete | Deep foundations | Rockfill dams | Bays | Soil stabilization | Soil analysis

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