PRIEST RAPIDS RIGHT LAND IMPROVEMENTS
Mattawa, Wash.
Merit Award
Sent by: IMCO General Construction
OWNER: Grant County PUD no. 2
LEADING DESIGN COMPANY: Stantec
GENERAL CONTRACTOR: IMCO General Construction
Originally built in 1958, Priest Rapids Dam is a composite structure with a center channel spillway and powerhouse and left and right embankments. Through proactive hazard identification modeling, the client discovered that the right abutment embankment dam was susceptible to failure under seismic events. This $60.9 million project was intended to provide a backup dam should the existing levee dam fail, ensuring the safety of the neighboring Wanapum Indian Tribal Village located immediately downstream and protecting lands used for traditional cultural practices. To mitigate impacts to the village during construction, the entire project was also subject to strict work schedules.
The scope of work included a 55 feet high by 1,785 feet long roller compacted concrete (RCC) dam constructed downstream of the existing right embankment. Beyond the liquefiable zone, the RCC dam is reconnected to the existing embankment by a new 250-foot-long earthen embankment, further reinforced by a bentonite-infused plastic concrete shear wall drilled through the new embankments and existing The wall is 60 feet deep and 300 feet long and is composed of piles 10 feet in diameter with rock plinths 5 feet to 10 feet.
The contractor operated two batch plants of its own to produce concrete materials including RCC, conventional concrete and plastic concrete. At peak production, the plants manufactured more than 1,300 m3 of material per shift.
