Fort Laramie Tunnel No. 2 Collapse and Repair—Lessons Learned

Tunnel No. 2 is one of the three tunnels along the Fort Laramie Canal constructed between 1915 and 1924. The tunnel suddenly collapsed in July 2019 and soil from nearly 100 ft of noncohesive formation above the tunnel plugged the tunnel terminating the flow. Failure analyses showed that deteriorated timber forms over time, movement, and internal erosion of fine material resulted in voids forming behind the lining. These voids lead to cracks developing in the lining. Eventually a cracked lining section in the crown collapsed initiating a catastrophic collapse. The lessons learned from this tunnel failure include continue periodic inspection of facilities to maintain a dynamic data-base about infrastructure conditions as well to classify associated risks, migration of fines behind lining alter loading distribution on the lining, causes of cracks and offsets must be examined, and evaluation for repair methods of cracks, offsets, and voids require immediate attention.