What is the “Tunnel”?
The “Tunnel” is a major part of the drainage system improvements that are being constructed for I-75 Segment 3. This storage and drainage tunnel system is 4-miles long, 14.5-foot diameter and 100 feet underground generally along I-75’s northbound service drive between 8 Mile and 12 Mile Roads.
Why do we need the Tunnel?
|Photograph: Michigan State Police boat patrols on I-75 at I-696 in August 2014|
The current drainage system is almost 50 years old and in need of improvements. In the summer of 2014, the Metro Detroit area experienced one of the worst floods to date. The 14.5-foot diameter, 4-mile long drainage tunnel will provide storage and conveyance to help avoid future flooding in the depressed portion of the freeway.
Where is the Tunnel located?
The main tunnel construction site is in the northeast quadrant of the I-75/I-696 interchange and work began in the fall of 2019 to construct a 100-foot deep shaft. The tunnel boring machine (TBM) will be launched from this shaft late-spring 2020 and will mine (dig) its way 100 feet underground north from the I-696 interchange to a pump station located just north of 12 Mile Road. The TBM will then be removed and relaunched from the I-696 construction site south to a shaft site located near Meyers Ave (See map image below).
How is the Tunnel being constructed?
|Photograph: TBM Cutter and Shield Unit|
|Photograph: Front of TBM assembly|
The tunnel for I-75 will be constructed with a tunnel boring machine (TBM). A TBM is an automated machine with a rotating cutting wheel with teeth at the front that digs away at the soil while it turns. Miners in the tunnel install 5-foot long precast concrete wall segments within a shield to protect them. Hydraulic jacks at the back of the TBM push against the ends of the wall segments after they are installed to force the cutting wheel into the soil and move the tunnel forward. Behind the shield is a 300-foot long assembly of support equipment, including electrical, mechanical and ventilation equipment. A small locomotive on rail tracks will travel up to 2 miles between the TBM and the I-696 shaft with boxes to haul out excavated soil and flatbed cars to bring in the concrete wall segments.
Once completed how does the Tunnel work?
|Photograph: Aerial view of Tunnel Construction Shaft at the I-75/ I-696 Interchange|
Storm water is collected from the I-75 freeway and service drives in a network of pipes that direct flows into seven “drop shafts” (large pipes). These shafts connect to the tunnel below, where the storm water then flows north to a new pump station just northeast of the I-75 and 12 Mile Road interchange. The pump station lifts the water nearly 100-ft and discharges it into the Oakland County Water Resources Commissioner (OCWRC) Retention Treatment Facility.
When will the Tunnel and pump station be completed?
The tunnel work began in the Fall of 2019 and is scheduled to continue through 2022. Once the tunnel boring machine is launched in late-spring 2020, the TBM will travel north from the I-696 interchange to the 12 Mile Road pump station which will take nearly ten months. The TBM will then be removed from the 12 Mile Road pump station and be relocated back to the launch site at the I-696 interchange. Once relocated, it will begin working its way south to the Meyers Avenue shaft site which will take nearly nine months to complete. After the TBM has completed its job, it will be removed from the ground and decommissioned (taken apart) as crews complete pump station and drop shaft work and finalize the tunnel drainage system.
Historically, a Tunnel Boring Machine is generally named after a woman as a sign of good luck for the project ahead. Naming digging equipment after women is a tradition that dates to the 1500s when miners prayed to Saint Barbara to keep them safe underground. Workers looked to Saint Barbara for protection as she is the patron saint for military engineers, miners and others who work underground.
The TBM for this project was named “Eliza” after a community vote through the OCP website. https://ocp-i75.com/tbm-naming-contest
Eliza Seaman Leggett was chosen as she was an active participant in the Underground Railroad and her Waterford Township home in Oakland County was a stop on the legendary Underground Railroad. Upon the end of slavery, Ms. Leggett turned her attention towards the suffrage movement and helped women in need. During the 1870s she devised, co-founded, and implemented the Young Woman’s Home Association for the young working women of Detroit. She was instrumental in making Belle Isle a public park for the people of Detroit. She also ensured that public drinking fountains and horse watering troughs were placed throughout the city of Detroit.