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City of Bethlehem - Penn Forest Dam

Penn Forest Dam, which is a roller-compacted concrete gravity dam, is 160 ft. high and 2,000 ft. long. It is 115 ft. wide at the bottom and the top section is 30 ft. wide. The Dam is constructed of approximately 380,000 cu. yds. of roller-compacted concrete making it the third-largest roller-compacted dam (by volume) in the U.S. and the largest east of the Mississippi River. It is located approximately 460 feet upstream of the centerline of the existing earth embankment dam and aligned to make full use of Penn Forest's existing spillway and outlet works. Dam construction required 800,000 tons of raw material (sand and stone), which amounted to 38,000 truckloads of material. Concrete was poured 24 hours a day, seven days a week.

The new dam is buttressed on the downstream face by earth material from the existing embankment. The fill was placed concurrently with the RCC, providing a form for the downstream slope. In addition, the buttressing effect of the earth fill provided an opportunity to structurally reduce the gravity section required for stability, thereby allowing the RCC to be placed on a steep 2:1 vertical-horizontal slope. That means the gravity section relies on the existing embankment only for minimal support. A minor failure of the embankment would not have a significant impact on the dam's overall performance. That also helped to reduce maintenance requirements. The alignment and location of the RCC dam resulted in a savings of about $20 million compared with a new stand-alone dam.

Butz's fast-track approach to the project saved the City of Bethlehem $7 million and cut 7 months off the project duration.



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