Orofino, Idaho
September to December 1997
Constructed in 1972, Dworshak Dam is the third highest dam in the United States. Since its commissioning, seepage rates through the gallery relief drains have increased steadily, reaching approximately 3,000 gpm by 1996.
The grouting program undertaken to reduce the seepage involved four processes:
- Construction of a semi-permanent barrier by injecting cement based suspension grouts and hydrophobic, water reactive polyurethane via MPSP systems through the existing relief drains.
- Construction of a permanent, double row grout curtain upstream of the relief drains using regular cement based grouts.
- Installation of new downstream relief drains.
- Remedial grouting of the vertical joints between the monoliths, utilizing a flexible foam filled with bentonite slurry.
ECO acted as a sub-consultant to the contracting joint venture, providing the method statement and methodology for the grouting techniques employed.
The latest results from the new relief drains show that the grouting program reduced the total seepage from 3,000 gpm to less than 100 gpm.