Hampton Roads Midtown Tunnel, US
Integritank® application and in-situ performance ensures waterproofing success at busy tunnel.
The Hampton Roads Midtown Tunnel was originally built in 1962 under the Elizabeth River to ease traffic in the Hampton Road area. However, with a local population increasing by nearly 70 per cent to 1.6 million, and the tunnel traffic flow increasing by 350 per cent during its fifty-year lifetime, finding a solution was critical.
Despite being a key route between Norfolk and Portsmouth, the tunnel wasn’t equipped to deal with the increasingly higher volumes of traffic. While in 1962, the tunnel saw 8,400 vehicles passing per day; by 2015 the number was estimated at 38,000. As the main access to the local Virginia Beach, the tunnel sees many more users passing through in the summer months.
The original structure consisted of two lanes with bi-directional traffic; meaning traffic flow was severely restricted. A new two-lane tunnel was constructed, adjacent to the original, enabling one-way traffic in each tunnel.
Virginia Department of Transport
SKW Constructors consisting of Skanska USA Civil Southeast, Kiewit Construction Company and Weeks Marine
- Hampton Roads Midtown Tunnel, USA
Integritank® was selected as the waterproofing membrane of choice following a proven track record on high profile immersed tube tunnel projects in Hong Kong, Mexico and the Middle East. The original plan for the project was to use crack proof concrete instead of a waterproofing membrane, but this couldn’t guarantee the same level of waterproofing. Instead, Integritank was specified as part of a long-term asset management plan, to help lengthen the working life of the tunnel.
The new second all-concrete tunnel measures 1,280m, making the total tunnel length 1,658m. For the new tunnel construction, there were two litters of tunnel elements, containing a total of 11 segments. Each tunnel element was 106m long and weighed 16,000 tonnes.
The two litters had to be constructed off-site in Maryland due to the large size of the segments, and the fact there wasn’t a dry dock big enough in the area. The tunnel segments were constructed off-site at a dry dock in Sparrows Point, Maryland. Once Integritank had been applied to the external walls and roof of the tunnel, the dry dock was flooded and the tunnel elements immersed, to confirm they were completely watertight.
The 11 segments were then towed 220 miles down the Chesapeake Bay to Virginia, one at a time, in two separate phases (six segments in the first phase in 2014 and five in the second in 2015), where they were immersed sequentially.
A total of 33,500m2 of Integritank membrane was spray applied to a thickness of 2mm in two coats, with the waterproofing phase finishing in March 2015. A number of quality assurance tests were carried out, including checking the wet film thickness every 10m2 to ensure a minimum 1mm in wet film thickness for each of the two coats applied. Further tests were carried out to check that the adhesion to substrate every 500m2 was in order, to achieve a minimum adhesion of the membrane value of 0.7 MPa. Actual adhesion values on the project were far in excess of this requirement. Consumption rate checks also ensured adequate quantity of material had been installed for each phase of work.
Tom Carter, vice president at Stirling Lloyd in the US comments: “Despite the scale of the project and the poor weather conditions in the winter of 2014, with heavy snowfall, the waterproofing of the Hampton Roads Midtown Tunnel was successfully carried out, on time and within budget. The waterproofing system is expected to last longer than the design life of the tunnel. The new tunnel has also been effective in easing congestion in the area, cutting journey times by 30 minutes. With 1.6 million people living in the region, this has been a significant benefit.
“The client was also safe in the knowledge that if any damage was sustained while transporting the waterproofed segments, the technology within the Integritank membrane together with Stirling Lloyd’s technical skills would enable underwater repairs to be undertaken ensuring an in-situ, waterproof tunnel."
Rob Hollinger, President of Venture Construction, the approved applicator that installed Integritank, comments “This is the second immersed tube tunnel we have waterproofed in North America using Stirling Lloyd’s Integritank. Venture has the experience not only in terms of the application expertise of Integritank, but also in terms of surface preparation and familiarity with immersed tube tunnel applications, to ensure future projects are equally successful.”
The scale, location and economic importance of the new Hampton Roads Midtown Tunnel meant that maintaining water tightness throughout the towing and immersion procedure and then once in-situ was of paramount importance. The use of Integritank ensured a tough, durable membrane that not only met this requirement but will extend the service life of the tunnel and reduce maintenance costs throughout its lifespan.