Category: Applications

The original Tappan Zee Bridge, spanning the Hudson River between Tarrytown and Nyack in the state of New York, was completed in 1955. By the 2000s, it was deemed decaying and overburdened. The collapse of Minnesota’s I-35W Mississippi River bridge in 2007 raised worries about Tappan Zee’s structural integrity.

A new, twin cable-stayed bridge was built a few yards north of the original bridge by Tappan Zee Constructors LLC (TZC), a consortium of firms. The Left Coast Lifter — a huge crane on a barge previously used to replace a span of the San Francisco-Oakland Bay Bridge — was used to install groups of pre-assembled girders one full span at a time. Construction of the new bridge and demolition of the old one overlapped, with the entire project completed in May 2019.

The project was huge, complex and on an accelerated schedule. “Challenges included the size of the bridge, the river’s current, tidal variations, the water’s turbidity and strong winds,” recalled Jonathan White, product manager for Trimble Civil Construction Field Solutions, Marine. Conditions were particularly challenging for bathymetric data collection before and during the project. “The low visibility in the water made it a prime situation for sonar technology to play a major role.”

A licensed surveyor conducted a pre-dredge bathymetric survey, which was loaded into the construction software as a baseline. Trimble hardware, software and technical advice supported the demolition of the old bridge.

“As they were beating down the bridge with the jack hammers and trying to pick up the rubble from the river with the cranes, the main challenge was to keep the 11 machines that they had updated in real time with the most accurate 3D data, so that they could keep working,” explained Nathan Keys, a geospatial engineer at Measutronics, a Trimble dealership and project lead for the Tappan Zee Bridge project.

Rather than mount a sonar to the front of each construction barge, they used a single survey vessel to serve the machines (eight excavators and three clamshell cranes) with real-time data, using networked connections to update one machine at a time.

Whenever a crane operator thought he was done in an area — the machine guidance display in his cab told him that he had achieved the design depth — the survey boat would verify that, and either give the operator the go-ahead to continue working or point out any spots that were still too high or too low. “That way, they would avoid having to return to an area, which costs time and money,” Keys said.

Trimble equipment provided the positioning of the machines, tracked their motions, and visualized them, enabling the operators to “see” underwater where their bucket, grapple tool, clamshell, or other tool was operating. Trimble supported its dealer and the consortium that was executing the project, White said. “Measutronics is very well versed in the capabilities of Trimble equipment and, more broadly, marine construction workflows generally. If a piece of their equipment went down, we could swap something out and provide them with any support that they needed, and expedite that support because we knew how crucial it was with them being in the field pretty much 24/7.”

Marine excavation. The survey vessel was equipped with a Teledyne RESON T-20 multibeam sonar and a Trimble Applanix POS MV WaveMaster for motion and position. “The eight excavators were equipped with a Trimble marine excavator guidance package, which includes a GPS receiver and angle sensors working together to give guidance to the tool, whether it is a jack hammer, a bucket or whatever,” said Keys. “They also had three clamshell cranes with rotational encoders on the wire-out drums, to keep track of the bucket’s vertical. The central piece to all this is the Trimble Marine Construction software, which takes in the data from all the sensors, including the sonar, in real time and updates the display in the cabin.”

To install its sensors on machines, Trimble provides flexible aftermarket kits that come with weld plates. “We just point out to the customer where to weld the plates, then we will put the sensors on, run the cables to the cab, and do all the wire runs,” Keys explains. “It does not matter whether it is a Caterpillar or a Kobelco or whatever. They are aftermarket systems, so they can go on pretty much any machine.”

This project, Keys clarified, involved only machine guidance, not automation. “We were not using any of the machines’ own sensors. We showed them where they were and then the operator would have to control it.”

Trimble provided precise position and heading, White said. “Through a very accurate measure of where each of these sensors is installed relative to the phase center of the GPS antenna, we can determine how the machine is moving and measure that movement, so that we know exactly where the tool is relative to the position that we are getting from our satellite trilateration. It is not like the guy is sitting in the seat drinking a cup of coffee while the machine parallel parks itself. However, he is receiving a lot of information from all those sensors as to his tool’s position relative to that GPS location.”

Keys said the machines constantly log the data and their movements while they are running. “We can go back into those log files and pull out whatever we want,” he said. “On the survey side, when they do a scan or a survey of an area, that data is captured as a 3D point cloud of what the bottom looks like, which you can import into any software to visualize and quantify the riverbed and the rubble.

“The availability of that real-time sonar data kept those machines productive,” Keys said. “It keeps them from having to go back and do any kind of re-work.”

White said the technology is getting more affordable and user-friendly. “That is leading us, as a manufacturer, to look for ways to help further bring it into our standardized workflows. We have been working with Teledyne on those objectives.”

Trimble is also keen to advance the networking component, specifically to the marine sector, White added. “It is relatively new to marine construction projects. The ability to have a sonar vessel speaking to a machine, and all the machines to speak to each other, and to share a survey file is a very important objective for us.”