Work on the Ellicott City North Tunnel Project in Howard County, Maryland is advancing toward a key transition point as the team prepares for tunnel boring machine (TBM) assembly following recent progress on deep excavation and equipment mobilisation.

The tunnel is a central element of the county’s Ellicott City Safe and Sound flood mitigation programme, designed to divert stormwater flows away from the Historic District and into the Patapsco River, reducing the risk of devastating flash flooding in the community.

Recent Construction Progress

• Second Chamber Excavation Complete
  Excavation of the second shaft chamber — part of the deep launch and retrieval shaft complex — is finished. These shafts, approximately 49 m deep, will house the TBM launch and support structures for the project.
• Cutterhead and TBM Preparation
  A refurbished Robbins Main Beam TBM, named Rocky, has completed factory acceptance testing following a rebuild in partnership with contractor Kiewit and is scheduled to arrive on site for assembly.
• TBM Launch Imminent
  Robbins’ main beam machine is expected to be assembled at the launch site in early 2026, after which tunnelling operations will commence.

Project Scope

The Ellicott City North Tunnel is being delivered by the Kiewit-Traylor Joint Venture, which is providing construction manager at-risk services for the project.

Once complete, the tunnel will:

• Convey stormwater flows beneath Ellicott City at depths exceeding 100 ft;
• Stretch approximately 1 mile (1.5 km) in length;
• Have a diameter of roughly 5.6 m (18.4 ft);
• Be capable of transporting up to 26,000 gallons per second directly into the Patapsco River during high-intensity storm events.

The tunnel will be excavated largely through granite bedrock, reducing surface disruption in the densely developed, historic urban environment.

Technical Features

• TBM: 5.6 m diameter Robbins Main Beam machine, extensively refurbished and tested.
• Alignment: Deep underground beneath Ellicott City’s West End and Main Street areas.
• Excavation method: Mechanised tunnelling via TBM through predominantly hard rock.

Contract and Funding

• Contractor: Kiewit-Traylor Joint Venture (KTJV).
• Delivery Model: Construction Manager at Risk.
• Funding: The project has received multiple state and federal funding advances, including an $18.2 million allocation from the Maryland Board of Public Works toward construction of the tunnel segment.

Schedule and Outlook

• TBM Assembly: Expected early 2026 following delivery and site preparation.
• Tunnelling Operations: To begin once TBM is launched.
• Completion: The tunnel excavation is projected to be substantially complete by late 2027.

Significance

The Ellicott City North Tunnel represents one of the most ambitious stormwater conveyance projects in Howard County’s history and a core element of a broader flood mitigation strategy in a region repeatedly impacted by severe flooding. Its deep, mechanised tunnelling approach, combined with a refurbished, proven TBM, underscores the technical commitment to delivering resilient underground infrastructure with minimal surface impact. 09/26.