Tilson Wires the Big Dig for LTE Communications

The Central Artery/Tunnel Project, what we all know as the “Big Dig,” is arguably the most complex engineering project ever taken on in the U.S. Unforeseen civil engineering challenges cropped up that called for exceptional innovation. After more than 15 years, the tunnels – including the Ted Williams Tunnel and Tip O’Neill Tunnel – and the widest cable-stayed bridge in the world were finished.

Challenge

One part of the Big Dig that required attention after completion was the cellular communications system. The original 31-channel distributed antenna system (DAS) was another technology breakthrough, and set a new standard for in-tunnel communication. It was enhanced by AT&T with 2G cell phone service in 2008. When 4G technology came along in 2010, AT&T called on Tilson to upgrade the fiber and wireless systems in the Ted Williams and Tip O’Neill tunnels for LTE connectivity, including overhauling the system from the extreme wear and tear of several years of wet salt spray, exhaust gasses, temperature extremes and vibration.

 

Step one was assessing the condition of the network. Tilson discovered that the acid wash that maintenance crews used to clean the tunnels also eroded the protective coating on network connectors. Salt spray splashed by vehicles, and the pervasive damp climate, set up perfect conditions for corrosion. Time had taken its toll as well on the base stations and electrical services equipment.

A big logistical and worker safety issue was the fact that work needed to go on while the tunnel was in use – and traffic never stops.

Solution

Installing the LTE upgrade to the DAS system was relatively straightforward: Tilson upgraded and replaced inside and outside plant cabling, installed and racked head-end equipment, added and repaired electrical drops and powered antennas, and integrated fiber and wireless nodes throughout the tunnel systems. Commissioning and testing were the last steps of the two-month project.

 

To mitigate the impact on traffic, Tilson coordinated efforts with the Massachusetts Department of Transportation. Tilson’s team worked above travel lanes and concentrated their effort during off-hours and in adherence with other traffic control restrictions, including joining with other road maintenance crews in the tunnel to minimize lane closures to the public.

Then, there was the corrosion problem. Replacing the old connectors with the same product was a stop-gap, unacceptable approach, although the easiest solution. Experimenting, Tilson found that by applying a powder coating and then dipping the parts in liquid truck bed liner, the enamel coating on connectors would not chip. In fact, that innovation appears to be a permanent solution; the connectors should never need to be replaced.

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