- Emergency response after collapse to restore canal flow as soon as possible.
- The soil that flowed into the tunnel through the collapse completely plugged the tunnel with a saturated, unstable “bulkhead” that had to be supported as it was excavated to prevent further collapse and to protect the tunnel workers.
During the early morning hours on July 17, 2019 a collapse in Tunnel 2 on the Fort Laramie Canal caused water to back up and breach the canal bank upstream of the tunnel. The Fort Laramie Canal provides irrigation water to approximately 104,000 acres in Wyoming and Nebraska served by the Goshen and Gering-Fort Laramie Irrigation Districts and the Wright and Murphey Ditch Company. Brierley Associates was employed by the tunnel repair contractor to oversee the grouting operation and investigate the condition of the tunnel. Following the emergency response, the Owner’s Engineer, Anderson Consulting Engineers, Inc., retained us to continue work on the permanent repair/replacement solution.
The tunnel was constructed by the USBR in 1917 with timber supports. The tunnel is approximately 14-ft high by 14-ft wide in a horseshoe configuration with an unreinforced concrete liner.
Brierley Associates provided emergency engineering support involving initial assessment, inspection of the concrete lining and adjacent voids, and design of temporary steel set supports, a void-filling grouting program, and other temporary measures to repair the collapsed lining to restore water flow in the canal. Later, Brierley inspected two other tunnels on the canal and provided repair and support recommendations to prevent additional collapses. Brierley is continuing to work on evaluation, cost estimating, and design of alternative permanent repair options for the owner.