Safe from Floods with DYWIDAG Anchor Systems: Reinforcement of the Folsom Dam in California

Completed in 1955, Folsom Dam is located on the American River in northern California, approximately 40km northeast of the city of Sacramento. The 100m (340ft) high and 430m (1,400ft) long dam creates the Folsom Reservoir that has a maximum possible water area of 4,830ha (11,930 acres). The Folsom Power Plant has 3 Francis Turbines with a total output of 198.72MW.

In order to significantly lower the probability of floods and to double the amount of water the dam can hold in the event of flooding, the U.S. Army Corps of Engineers and the Central Valley Flood Protection Board cooperated with the state of California and the Sacramento Area Flood Control Agency to undertake the “Joint Federal Project” (JFP).

The JFP includes a new spillway with six submerged tainter gates located in a new control structure. This structure is an additional dam that prevents water from entering the spillway when the gates are closed. The project consists of 5 phases.

In phase IV of the construction, a 335.3m (1,100ft) long approach channel is being built for the new spillway on the reservoir side. Essentially, this includes a second dam, the 922.6m (3,027ft) long spillway chute and the stilling basin on the downstream side.
The stilling basin works as an energy dissipater to slow the water as it enters the American River.

In this phase, the soil for the additional dam and part of the spillway chute is excavated, and the foundation of the control structure is built.

For this purpose, DSI Construction USA supplied a total of 316 90mm Ø DYWIDAG Rock Anchors consisting of 168t of galvanized THREADBAR® Tendons that were installed in the approach slab of the spillway chute.

Furthermore, DSI supplied 75mm Ø, GR 150 THREADBAR® Tendons to extend the 30 rock anchors that were installed in phase III as well as the complete stressing equipment and a grease pump. The technical challenge was to develop four different customized anchor geometries to extend just 30 anchors.

The rock anchor systems supplied by DSI proved to be superior to those of the competitors. Furthermore, DSI was able to secure this project by taking advantage of its high quality products and excellent customer service.


US Army Corps of Engineers, USA

General Contractor

Kiewit, USA


Neil’s Controlled Blasting, L.P., USA


US Army Corps of Engineers, USA

DSI Unit

DYWIDAG-Systems International USA Inc., BU Geotechnics, USA

DSI Scope

Production, supply

DYWIDAG Products

316 90mm Ø DYWIDAG Rock Anchors, 75mm Ø THREADBAR® Tendons, stressing equipment and grease pump

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