Underground & Tunnels
Poe Tunnel Liner Repair
Butte County near Oroville, California
Poe Tunnel is part of the Poe Project; comprised of a diversion dam, reservoir, and concrete intake structure along the shore of the reservoir at the upstream end of the tunnel and a surge tower, steel underground penstock, and powerhouse at the downstream end. The tunnel is approximately 18-feet in diameter and 6½ miles long with concrete-lined and unlined sections. The intake at Poe Dam is located in the Feather River Canyon at Poe Dam Reservoir, approximately 30 miles north of Oroville in Butte County, California.
The major scope of work activities included:
- Developing ventilation at the Poe Dam intake structure access point to pull fresh air through the tunnel,
- Helicopter support to fly equipment, materials, supplies, fuel, and portable toilets to two remote access adits (Adits 1 and 2),
- Cleaning debris out the three chambers of the rock trap,
- Repairing cracks in the existing concrete tunnel liner, including temporary shoring and scaffolding,
- Installing ten 1-inch diameter threaded bar anchors in the tunnel invert at the crack repair area (where it was observed to be lifting) to prevent further movement,
- Exposing the existing drain valve at Adit 1 and cleaning out the debris from the pipe to determine if the valve is operable, and
- Pumping grout into cracks in the concrete liner, along the invert of the tunnel, to fill voids where underlying material had washed away.
The repair work was performed during a planned outage and was conducted in strict accordance with Cal/OSHA – Title 8, Tunnel Safety Orders, due to the limited access from the intake and through the two remote adits.