Laramie-Poudre Tunnel Rehabilitation North of Fort Collins, Colorado
The Laramie-Poudre irrigation tunnel had a major collapse one mile from each
portal.
The Laramie-Poudre Tunnel Rehabilitation included mining through a major
cave-in one mile from each portal.
The project had to be investigated, designed, bid, and constructed within 10 months,
to convey water for the next irrigation season.
Several factors made the Laramie-Poudre Tunnel rehabilitation a challenge. The tunnel
is located at an elevation of 8,400 feet, 45 miles up a narrow canyon in the Rocky
Mountains. Transporting crews, equipment, and materials to the site was difficult.
The project's location on a Wild and Scenic River in the National Forest resulted in
stringent environmental restrictions.
This figure illustrates the large chimney that developed above the tunnel and the
steel rib canopy that was constructed through the caved section.
Part of the underground challenge in the tunnel was the size restrictions resulting
from variations in cross-section dimensions from different types of support. Only
the smallest equipment could be used, but it had to be able to mine through all of
the caved material, which ranged from clay to large boulders.
Laramie-Poudre Tunnel Timber Barrel.
The solution required the use of equipment and expertise from two generations ago
coupled with modern technology and new ideas. The tunnel was mucked out using
air-powered, overshot muckers dating from the 1950's, while the area above the steel
sets was filled with cellular concrete, a very recent innovation. The old timber sets
were lined with custom-made expandable conduits, cellular concrete, and shotcrete to
make a modern water tunnel. This combination of old and new required close collaboration
with the contractor, making use of innovative ideas and adjusting to field conditions.
Deere & Ault staff was selected because of the firm's expertise in water tunnels
and its reputation for working efficiently with contractors.
Deere & Ault continues to be involved in the monitoring and maintenance of this
tunnel.
