Reconstruction of the Initial 400 Ft of the Spiro Tunnel-PPT Presentation

PPT Presentation

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The Spiro Tunnel began construction in 1916 to drain a mine and support mineral exploration. After mining ended, it briefly served as a skier subway from 1965 to 1967. Today, it carries 4,000–8,000 gallons of water per minute and supplies about 35% of the city’s municipal water.<br /><br />The tunnel’s entrance was unstable, with a partial collapse, deteriorated steel supports, and an outdated water collection system that lacked flow controls. Rehabilitation plans called for excavating and stabilizing the portal, reinforcing the hillside, enlarging and supporting the first 400 feet, and installing two transmission lines to improve water-source separation and distribution. Historic features—including the rail, stone retaining wall, work platform, portal gate, and timber façade—were to be preserved.<br /><br />Crews used soil nails, drainage measures, rock bolts, and steel-fiber-reinforced shotcrete to stabilize the ground. Highly fractured rock caused grout loss, while hazardous scaling required careful removal of only unstable material. Some sections opened into unexpectedly large chambers, requiring longer bolts and thicker shotcrete.<br /><br />Construction also faced flooding when a damaged pipe could not carry tunnel flow. Temporary sandbag barriers and pipe repairs allowed work to continue, while repeated pipe crushing made trenching necessary. The project also included upgrades to the junction room, piping, vault, and portal structure.

Keywords

Spiro Tunnel

mine drainage

mineral exploration

skier subway

municipal water supply

tunnel rehabilitation

portal stabilization

shotcrete

soil nails

historic preservation