Project Overview
The 5.2-mile Michigan Ditch conveys transmountain fresh drinking water for City of Fort Collins residents. A slow-moving landslide imparted damage to various portions of its above-ground piping network, and its continuous restoration had been a burden on the City. The damage reached critical mass when a landslide moved a large section of the delivery system a significant distance. The City of Fort Collins recognized the water source as one of their communities’ most valuable commodities and put together a team of experts using an Alternative Product Delivery System model. The team decided to re-route and permanently protect the most vulnerable portion of the aqueduct by constructing a 98-in. OD ring-beam and lagging through Never Summer Mountain. The 766-ft. tunnel featured a 630-ft. radius curve, to be completed with 60-in. OD carrier pipe.
Challenges
• High-risk tunnel in highly fractured pegmatite and gneiss ground conditions
• Required construction between the snowfall end in the spring and when it began again in late fall
• Remote project site more than 30-miles from the closest city • Considerable site preparation before tunneling equipment was mobilized
• Careful scheduling and staging to safely transport equipment without exceeding access road weight limits
Solution
BTrenchless ordered a customized TBM system package:
• 720 Series II TBM with TBM stabilizers and the maximum number of TBM drive motors
• 98-in. mixed-ground disc cutter head, designed to excavate up to 15,000 psi rock with back- loaded tooling mounts
• Propulsion can for the TBM to advance off of the constructed tunnel
• Dual extended belt conveyors to extend through the TBM and propulsion can for maximum tunneling efficiency to excavate one ring set within two haul unit cycles
• A standard 5200 Pump Unit with a 200 HP Auxiliary Pump
Outcome
• A challenging project exceeded all of its goals
• The collaborative approach of the ADPS model resulted in nearly $1 million in project savings
• The project will provide reliable drinking water for City of Fort Collins residents for many years
