- Two 96-in diameter tunnels crossing under 17 active railroad tracks and 2 commuter rail lines
- Challenging mixed-face ground conditions
- Construction/demolition debris within tunnel horizon
- Running sands, shallow tunnel
- Grouted pipe canopy helped mitigate dangers posed by debris
- “National Recognition Award” American Council of Engineering Companies, 2021
Globeville Landing Outfall Tunnels are part of the Platte to Park Hill wet weather stormwater flooding solution developed by the City and County of Denver. Consisting of twin 515-ft long 96-inch diameter tunnels passing under 17 active Union Pacific Railroad (UPRR) and two Regional Transportation District (RTD) tracks was one of the many project challenges
During the design phase, mixed-face conditions consisting of well-graded sand with gravel zones and lean clay were identified and there were indications of a buried pipe was within the tunnel alignment. However, the condition and location of the pipe were unknown until construction. During the first tunnel drive utilizing a microtunnel boring machine (MTBM) a zone of crushed and intact concrete made it difficult to maintain machine slurry pressure. Another challenge encountered during the first tunnel drive was construction/demolition debris – wire, steel, PVC, asphalt, and wood.
To overcome the first tunnel drive challenges posed by the construction/demolition debris the design and construction teams collaborated to devise a solution comprised of a grouted pipe canopy. Additionally, consolidation grouting was performed from the ground surface into the crushed concrete pipe zone. Implementation of this solution was key to successfully complete the second tunnel in less than one day
Brierley Associates served as trenchless/microtunneling specialist to the design team for the City and County of Denver. We delivered: Geotechnical Engineering and Data Report, Geotechnical Baseline Report, Basis of Design Report, specifications, and drawings for the twin tunnels. Brierley also worked closely with the design and construction teams and, the City and County of Denver to develop solutions to challenges that arose during construction and perform quality assurance during tunneling and grouting operations.