Linking Resources and Communities

A public-private partnership is delivering a multi-faceted highway and tunnel infrastructure project in Southeastern Virginia that will make transportation between the cities of Norfolk and Portsmouth safer, faster and more efficient for decades to come. 

 

By Dallas Marlow, P.E.  

   


 tunnel being built under Elizabeth River

Crews conduct test installation of new jet fans installed in the I-264 West Downtown Tunnel, one component of the Elizabeth River Tunnels Project. The fans will reduce CO₂ levels, improve air quality and provide enhanced smoke and heat control in case of a fire. PHOTOS COURTESY THE ELIZABETH RIVER TUNNELS PROJECT


 

When construction and rehabilitation of the $2.1 billion Elizabeth River Tunnels Project is completed in early 2018, commut­ing in the Hampton Roads area between Norfolk and Portsmouth, Va., will be safer, faster and more efficient.

The project was procured as a public-private partnership comprised of the Virginia Department of Transportation, as the owner of the infrastructure, and Elizabeth River Crossings OpCo LLC (ERC), as the private company responsible for financing, designing, operating and maintaining the project for a term of 58 years. ERC contracted with design-build contractor SKW Constructors JV, which is formed of Skanska, Kiewit and Weeks Marine, with Parsons Brinckerhoff as lead designer supporting the joint venture.

The scope of the work consists of several inter-connected infrastructure elements: a new, two-lane concrete reinforced immersed tube highway tunnel under the Elizabeth River adjacent to the existing Midtown Tunnel; rehabilitation of the existing Midtown Tunnel and the two Downtown Tunnels; and a new 1-mi, elevated four-lane extension of the Martin Luther King Freeway, which will connect all four tunnels along with Interstate 264 and Virginia Route 164.

 

MEETING INCREASED DEMAND

Since the original Midtown Tunnel was completed in September 1962, the popu­lation in the Hampton Roads region has increased nearly 70 percent. Tunnel traffic has increased by 600 percent. Nearly one million vehicles travel through each month. It is considered the most heavily traveled two-lane road east of the Mississippi River.

The Elizabeth River Tunnels Project pres­ents several unique innovations in design, construction and technology—as well as a few challenges. The original Midtown Tunnel is a concrete-encased steel tube tunnel. The new tunnel will be only the second concrete-reinforced immersed tunnel in the United States—although this method is used extensively across Europe. The concrete reinforced tunnel will allow ERC and SKW to provide the same end result as the original tunnel, but in a more cost effective approach and with greater flexibility in design.

The alignment of the new tunnel on the Portsmouth side of the Elizabeth River passes through an active marine terminal, crosses existing port access roads and rail lines, and descends to the river bed just north of the existing Midtown Tunnel. The new alignment also is in close proximity to an existing 42-in sanitary force main and an existing 30-in raw waterline. Design was tailored to protect existing infrastructure as much as possible.

The new Midtown Tunnel is a curvilinear design with the new approaches and tunnel portals immediately adjacent to the existing portals. This alignment ensures the dredge cut does not influence the stability of the existing tunnel and eliminates the need for Support of Excavation for five of the 11 elements to be placed. The tunnel is being founded on a screeded gravel bed placed at the bottom of a dredged trench.

Due to the proximity of the alignment of the new tunnel and the existing Midtown Tunnel, a Support of Excavation system was developed to support the trench, mitigate settlement and resist movement of the existing tunnel structure. Vibration and movement monitoring equipment was installed inside the existing tunnel. The Support of Excavation system was designed using a combination wall of HZ king piles and sheet piles. Marine excavations of up to 80-ft deep within the system, and a portionof the wall being open sided required a bracing system including walers, pipes, struts and a tie-back system comprised of 36-in pipe pile (raker pile).

The tunnel is being constructed by piec­ing together 11 concrete tunnel elements, averaging 106-m (350-ft) long, 8.5-m (28-ft) high, and 16.5-m (54-ft) wide. The tunnel elements were fabricated in Sparrows Point, Md., about 200-nautical-mi away, a four-day tow trip from Portsmouth and Norfolk. The location was chosen because it was the largest dry dock in the area allowing SKW to produce six elements at one time.

 

MATERIAL FABRICATION

The project called for a 120-year design life and had specific concrete performance criteria. It took over 100 trial batches before arriving at the final mix that was used to create the tunnel elements. Once the final mix was selected, multiple mock-ups and trials were completed to test placement and thermal control methods before starting fabrication of the actual tunnel elements.

Each of the 11 elements was fabricated in five segments. And each segment consisted of three concrete placements. The inverts were placed first, then the center wall, and finally the outer walls and roof, also known as the doghouse. Once concrete placement was completed for a tunnel element, the next phase of the process began. This comprises sealing and waterproofing the elements; installing four temporary, inte­rior ballast tanks; and installing temporary bulk heads on each end, which allows the elements to float.

Once ready to be delivered, each of the 16,000-T concrete elements was prepared with all the equipment needed to be safely towed down the Chesapeake Bay from Sparrows Point to the construction site. One of the more challenging parts of the journey is passing through the Cape Henry Channel crossing over the tunnel section of the Chesapeake Bay Bridge-Tunnel out into the Atlantic Ocean, then turning the element in order to access the Thimble Shoals Channel and cross the other tunnel section of the Chesapeake Bay Bridge-Tunnel

As of February 2015, six of the 11 concrete elements are currently on-site, five of which have been successfully placed within the dredged trench under the Elizabeth River. The five remaining sections were scheduled to arrive in spring 2015.

  

BUILDING CONNECTIONS

The MLK Freeway Extension (terminus of Route 164) includes an interchange with I-264, a partial interchange with High Street in Portsmouth, and bridge crossings through urban Portsmouth incorporating aesthetic and lighting improvements.

The extension will provide a limited-access connection between the MLK Freeway and I-264. This will reduce congestion on local Portsmouth streets. The MLK Extension creates an efficient, connected transportation network, provid­ing direct access between the Downtown and Midtown Tunnels.

Rehabilitation of the existing Downtown Tunnels is taking place concurrently with construction of the new Midtown Tunnel and MLK Freeway Extension. Work began in August 2013 with the Westbound Downtown Tunnel. Rehabilitation of the Eastbound Downtown Tunnel began in July 2014. When work on the tunnels is completed, they all will feature brighter, more efficient LED lighting and an updated intelligent transportation system, which features 60 closed-circuit cameras with automated incident detection capability and dynamic message signs. A new jet fan ventilation system also will give the tunnels a two-hour fire rating at 100-MW. The system will reduce CO₂ levels, improve air quality and provide enhanced smoke and heat control in the event of a fire.

Structural repairs to the concrete barri­ers, roadway, replacement of missing tiles and the addition of fireproofing material to the tunnel ceiling are also key parts of the tunnel rehabilitation.

  

DELIVERING BENEFITS

Virginia’s Hampton Roads area is geographically very critical to national security with a number of military instal­lations in the greater vicinity, including Joint Base Langley-Eustis and Naval Station Norfolk, the largest naval base in the world.

When the Elizabeth River Tunnels Project is complete, the system’s average round trip user will save about 30 minutes a day, reducing fuel usage and cutting emissions. Roadway congestion also will be reduced. And from an economic perspective, the improvements will provide a key link to the various port facilities in the region, supporting the movement of goods in and out of these facilities.

 Investing in infrastructure improvements is an investment in improving the nation.

 


 

Dallas Marlow, P.E., is Construction Director, Elizabeth River Crossings OpCo LLC; 757-932-4422, or This email address is being protected from spambots. You need JavaScript enabled to view it..