Spirit Lake Tunnel Repair Spirit Lake, Washington

Deep within the Mount St. Helens Spirit Lake Outlet Tunnel, control points were established while laying out new support ribs. The project reached 6,000 feet into the tunnel and resulted in finalized as-built drawings for the 60-foot repair area.

Reproducing Tunnel Alignment Using Advanced Techniques in a Remote Location

In establishing survey control inside the tunnel and marking locations for work to take place, robotic total station survey equipment was used. A reproduction of the tunnel alignment was made to include a control map listing the record, as-measured control points, and alignment of the tunnel stationing. The remote location, conditions, and schedule made for a unique and difficult project: the tunnel, located over two hours from accommodations, was a mile and a half long and 11 feet in diameter, dark and strongly ventilated, with running water between two and 40 inches deep. Our crew worked 14 hours a day for five days, starting on a Friday. Because the work depended on weather and coordination with five agencies, the Otak team had to be ready to respond at any time and on any day of the week.