Reconstruction of the Initial 400 Ft of the Spiro Tunnel

The City of Park City recently undertook a renovation of the initial 400 ft of the historic Spiro Tunnel. The Spiro Tunnel is a historic mining tunnel along active ski lifts and ski slopes and speaks to the local mining history of the region. The tunnel is at least 14,000 ft deep and once it was decommissioned for mining purposes, served as a novelty chair lift in the ’60s, bringing guests up the mountain on what came to be known as the Skier Subway, a 45-minute ride through the tunnel ending at what is today’s Thaynes Vertical Shaft. The tunnel produces between 4,000 and 10,000 gallons of water per minute which is collected within the first 400 ft of the tunnel and flows under gravity to the Park City water treatment plant. It is estimated that the city gets approximately 30% of its municipal water supply from this source. The stabilization of the initial part of the tunnel included the deconstruction and removing of existing steel and timber sets in very fractured, blocky and angled rock-plane conditions followed by intensive bolting and shotcreting. The project was completed by replacing the two under-foot 24” water pipelines that ran at the base of the tunnel followed by the replacement of the rail ties and reestablishment of rail that runs inside the tunnel and provides a means of locomotion for maintenance and inspection. The project also involved extensive slope cut-back and stabilization at the portal and the installation of an architectural facade. The authors will discuss the overall project implementation including design and construction.