Innovations Cut Costs of a Power Plant's Water System

by R. Paul Narong,
Joseph Funston,

Serial Information: Civil Engineering—ASCE, 1983, Vol. 53, Issue 7, Pg. 46-49

Document Type: Feature article


A two-unit (660 MW each) coal-fired power plant in St. Clair, MI, requires 660,000 gallons of water for condenser cooling. A once through cooling system from the St. Clair River (one mile away) was selected, using four 9 ft 6 in. diameter prestressed concrete pipes (one intake and one discharge line per unit) in a common trench with a 14 in. diameter carbon steel common discharge diffuser in the river. Because of excavation depths of up to 30 ft and poor soil conditons, a full-scale test excavation was made to optimize the excavation side slopes from a flatter than 2:1 to a 1.5:1 slope. The trench excavation was made using a four cubic yard dragline and four cubic backhoe. A forklift was used to pick up the 20 ft lengths of pipe placed on wood cribbing in the bottom of the trench by a crane. Pre-construction field testing enabled a 12 in. thick unreinforced concrete bedding/work mat to be used instead of the usual 30 in., allowing for the weight of the construction equipment. Cement fly ash backfill instead of soil was placed around the pipe to 2 ft above the top of the pipe to save time, money, and manpower. The remainder of the trench was backfilled with previously excavated material. A major highway crossing was made by means of an open trench, with traffic detoured around the excavation. Existing underground utility lines in the vicinity of the highway were carried on a steel frame supported by steel pipes. Construction started in 1981 and the plant will go into operation in 1984 and 1985.

Subject Headings: Trenches | Concrete pipes | Steel frames | Steel pipes | Power plants | Innovation | Hydro power | Slopes | Michigan | United States

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