Reconstruction of the Initial 400 Ft of the Spiro Tunnel-Paper

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In 2020, Park City stabilized the first 400 feet of the historic Spiro Tunnel, an important water source that supplies up to roughly 35% of the city’s municipal water. The tunnel’s aging timber and steel supports were deteriorating, and rockfalls threatened both worker safety and the water pipeline beneath the tunnel floor.<br /><br />Work began by excavating the portal about 30 feet into the hillside to reach more stable ground. Crews stabilized the slope with soil/rock nails and reinforced shotcrete, then replaced the tunnel’s existing supports in short, carefully sequenced sections. Temporary bolts and scaling protected workers during removal; permanent support consisted of resin-grouted rock bolts, wire mesh, and shotcrete. Highly fractured, dipping bedrock caused substantial ravelling and large caverns, requiring longer bolts and thicker shotcrete in some areas.<br /><br />The project also replaced one 24-inch steel water line with two 24-inch HDPE pipelines, upgraded the collection bulkhead and surface diversion vault, and improved the portal and public-facing historic displays. Maintaining water service throughout construction was critical: temporary dams and bypass pumps kept flow controlled while the bulkhead and pipelines were replaced.<br /><br />The completed work provides a more stable tunnel, improved access for maintenance equipment, and a durable water conveyance system. Early contractor involvement and meticulous work sequencing were central to addressing difficult ground conditions, protecting crews, and avoiding disruption to the city’s water supply.

Keywords

Spiro Tunnel

Park City

water supply

tunnel stabilization

historic infrastructure

rock bolts

shotcrete

HDPE pipelines

water conveyance

construction sequencing