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11/13/2012
1
900 FOOT MICROTUNNEL UNDER INTERSTATE 70
Nate Soule, PE, PG – Brierley Associates
Tracy Lyman, PE, PG – Brierley Associates
Jeremy Ross, PE – Denver Water
Rocky Mountain Chapter NASTT
November 8, 2012
Project Purpose
• Owner: Denver Water
• Responsible for supplying water to the Northfield Stapleton development
• Conduit 151: 24‐36” potable water line
• Installation included two tunnels:
– 325 ft under Union Pacific Track
– 914 ft under I‐70
– Both used 42” diameter steel casing
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Stapleton Airport: 1929‐1995
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Caissons – To Remain in Place after demolition UH OH!
Spread Footings – MUCH BETTER!
Demolition of bridges in 1995
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Geotechnical Investigation – Buried Debris
Geotechnical Investigation
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Ground Conditions
• Contract did include a GBR
• Key Baselines:
– Interbedded sand and clay below the water table
– No obstructions
Construction
• General Contractor: Layne (Reynolds)
• Tunnel Subcontractor: Vadnais Corp.
• Dates: January to March 2012
• Equipment: Herrenknecht AVN800 MTBM and jacking system
• Outside diameter: 43.5 inches overcut of 0.75 inches
• Jacking System delivered 380 tons of thrust
• One interjack 60’ behind face
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Pipe 12+1
• ~250 ft into the drive
• Just before going under the freeway
• Advance rate dramatically slowed
• Debris including styrofoam, plastic, other fibers was coming out of the separation plant
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• Vadnais brought out a high pressure pump to attempt to clear the blockage and increase production
• The pump helped some and mining continued
• At least it wasn’t an abandoned cassion!
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• On April 4, 2012, the MTBM broke out of the ground
• On April 4, 2012, the MTBM broke out of the ground
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• On April 5, 2012, the MTBM is removed from the shaft
Drive Records• 914ft/21 days = 43.5 ft per day average
Best Day: 120 ftMarch 27, 2012
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Drive Records• Max Jacking force = 160 tons
• Capacity = 380 tons
• IJS was not utilized
160
Drive Records• Computer lost jacking data for the I‐70 drive
• All records were from hand notes
• Computer data was collected from the UPRR tunnel
• Come to Sacramento in February to see comparison of predicted to actual jacking loads
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Conclusion• 914 ft, 42” diameter constructed almost without incident
• Ground conditions were well predicted from the geotechnical investigation
• Stickiness of the clay slowed the advance rate below Vadnais’ predictions– Lesson learned for future tunnels with sticky clay
– Baseline it!
• Concrete rubble or abandoned cassions were not encountered
• No measureable settlement of the roadway
Questions