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Geotechnical Services for the Niantic River Bridge Replacement

Geotechnical investigation and design for one of Amtrak’s most complex capital projects.
  • Geotechnical investigation for the Niantic River Bridge Replacement--Gannett Fleming

    The 2,550-linear-foot retaining wall reduces impacts to the adjacent beach and wetland areas.

Client
Amtrak 
Location
East Lyme and Waterford, Connecticut
Our Role
Design, Geotechnical Investigations, Soil Borings, Rock Coring, Feasibility Study, Alternatives Analysis. 
Data
Construction Cost:
$104.7 million
Completed:
2010
Type:
New Construction
Outcomes
  • New approach embankments east and west of the river
  • 2,550 linear feet of prestressed-concrete sheet pile retaining wall
  • A two-tiered wall creates a grade separation for a walkway above the beach.

Gannett Fleming assisted Amtrak with the complete replacement of the Niantic River Bascule Lift Bridge, which is part of the northeast corridor. The bridge dates back to the 1890s and was extremely deteriorated. It is used by Amtrak, the Shore Line East commuter rail service of the Connecticut Department of Transportation, and the Providence and Worcester Railroad. The project’s proposed track speeds are designed to increase from 60 mph to 90 mph, with the track profile being raised six feet for greater clearance across the Niantic River.

Our firm performed final engineering services for the east and west approaches, including two miles of track realignment, signals, catenary, and precast-concrete retaining walls; and necessary geotechnical analysis and investigation for the new lift structure, retaining walls, and additional embankment material. 

What We Did

Our firm performed a feasibility study and alternatives analysis for embankment and retaining wall construction. The bridge replacement required construction of new approach embankments east and west of the river supported by 2,550 linear feet of retaining wall to diminish impacts to the adjacent beach and wetland areas. A prestressed-concrete sheet pile retaining wall was selected for support of the railroad and included cantilevered sections and sections anchored with piles, deadmen, and ground anchors. This system minimized environmental and railroad operational impacts, while simplifying construction by eliminating the need for temporary sheeting and dewatering. On the west approach, a two-tiered wall was created, utilizing a T-wall behind the concrete sheet pile wall to create a grade separation for a recreational walkway above the beach. 

The new bridge abutments are supported on prestressed, 16-inch square concrete piles, while the piers are supported on spread footings bearing on mass concrete extending down to saprolite. This combination provides cost-effective support for the new structure, while protecting the bridge from extreme scour events.

Key Features

  • Shallow groundwater
  • Soft organic silt and clay up to 50 feet thick and a peat layer up to 6 feet thick
  • Potential storm surge conditions on Niantic Bay and flooding in the Niantic River.

Sustainability Features & Outcomes

  • Retaining walls diminish impacts to adjacent beach and wetland areas
  • Prestressed-concrete sheet pile retaining wall helped minimize environmental and railroad operational impacts
  • A layered-stone scour-protection system was designed to protect the new walls and embankment from a 100-year storm surge event
  • Additional services included wetland delineation and asbestos investigation.

Awards & Recognition

Excellence in Construction Best in Show Award, 2013, Associated Builders and Contractors of Connecticut.

Similar Projects: Transportation: Bridges, Geotechnical: Foundations, Geotechnical, Transit & Rail: Railroad, Geotechnical: Retaining Walls, Transportation: Transit & Rail, Transportation