C+S July 2021 Vol. 7 Issue 7 (web)

Built to connect a network of surface track and underground tunnels, a railway system on the east coast was tasked with the systemwide installation of cellular service to provide increased safety and con- nectivity. While cellular service had already been available in all the train stations, there was still no continuous service available inside the tunnels, some of which were as much as 26 miles long underground. Constructed by assorted contractors, at various points in time, this unique system spans over 100 miles, has nearly 100 stations and pro- vides service for more than 600,000 customers a day. Converging as a cohesive entity, the track weaves back and forth, over and under, three states. The tunnels, which were built at various points in time, were hewn through rock and other materials on dif- ferent terrains creating an inconsistency in the exact configuration of tunnel interiors. Mobile Mapping Underground: They Said it Couldn’t be Done By Maraliese Beveridge

In order to design and build a modern communication system, a highly accurate as-built map of the entire system had to be created. Once completed, a series of cables could be attached to the tunnel walls that would provide the needed cellular service. Because the tunnel’s dynamic envelope has such limited space within, this map had to be of the highest quality available. Today we have the technology to do this and it’s called LiDAR. Light Detection and Ranging is a technology that uses sensors to scan a subject by sending out a physical pulse of light that measures distance based on the time of flight between when the pulse leaves the sensor and when it is reflected back and returns. This high-definition technology is so dense that it can measure over a million points per second per sensor. The term Mobile LiDAR refers to mounting high-accuracy mobile mapping scanners, in this case, to the top of a hi-rail truck that traverses the railway and scans while in motion. Mobile LiDAR depends on the use of Global Positioning (or GPS) technology for positional accuracies. Given that the tunnels were underground where GPS signals are not present, another method was needed. The team at Colliers Engineering & Design worked closely with the authority to develop a way to trick the GPS. So, how did they do it? The Team First, the railway authority had to find a team of professionals who were up for this challenge and approached Colliers Engineering & Design, at the time Maser Consulting–on their conviction that it could be done. Not only did the team have the right combination of equipment, after a

Typical tunnel LiDAR results with 3D cable position modeled



july 2021

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