The Magazine for Underwater Professionals
Mile Point scheme one of the first breakwater construction projects ever to use Trimble Marine Construction (TMC) software and Teledyne BlueView sonar to collect motion-compensated 3D point clouds and create a 3D model from the moving barge platform in real-time
Established in 1905, Manson Construction Company began as a small, family-owned Puget Sound marine pile driving business headquartered in Seattle, Washington, USA. Today, the company has more than 700 employees company-wide and a national presence in the US, with facilities in northern and southern California, Louisiana and Florida. Manson specialises in heavy marine construction and has extensive experience in dredging, waterfront construction and heavy lifting.
Recently, Manson was hired by the US Army Corps of Engineers to reconfigure part of the Mile Point channel in Jacksonville, Florida, to allow deep-draft container vessels to use terminals at JAXPORT without having to wait for slack tide. Amongst the Mile Point project’s many features was the construction of a 4000-foot (1200-metre)-long wall that will not only function as a breakwater, but will also retain dredged spoils and retrain the river currents.
Ken Quiñones, survey engineering manager for Manson, explains that the multi-phase, US$43.5 million (£33.4 million) project involved building a one-of-a-kind concrete structural unit (CSU) wall to retrain the channel where the Intracoastal Waterway and St Johns River converge. Historically, currents created by this bend in the channel resulted in difficult navigational challenges for commercial traffic. Large container ships were restricted to travel the St Johns River during two, four-hour periods of the day due to the tidal effects at this location. The Mile Point project was set in motion to ease cross-currents that have traditionally kept larger ships from transiting that section of the channel on ebb tide.
Project manager Patrick Kenning says that the Mile Point project’s multiple phases entailed excavation of not only a natural river bed but also the removal of a relic training wall, rock placement, marine mattress placement, geotube placement, CSU placement and dredging. The end result is two entirely new training walls (east and west leg training walls). The design of the west leg training wall, which includes the breakwater feature, required the placement of CSUs on top of rock filled marine mattresses and a uniform surface of native material or rock, which serve as the foundation.
During the bid process, Manson chose to partner with Trimble, USA, and Measutronics Corporation, USA, to develop a solid technological approach to deal with the need of critical plant positioning and the use of specialised acoustic imaging in shallow water. Measutronics is an authorised Trimble dealer and an expert in the application of marine construction technology. The company works with customers to solve complex marine challenges by integrating a full range of positioning systems, sonar, inertial motion, communication, attitude, software and echosounder systems.
“The Mile Point project was a complex job with many phases of work,” says Quiñones. “From our perspective, it required specialised machine guidance to accurately prepare the subgrade for where we would ultimately place the CSUs. With shifting tides and only three to four feet (0.9 to 1.2 metres) of water at low tide, the use of traditional acoustic systems would not have been an effective means to monitor our progress getting to grade. Additionally, we had to bring in material in some places, and we knew that getting the barge and excavator positioned safely and effectively in shallow water and meeting tight tolerances could be difficult. With the host of complicating factors, we looked to trusted partners and positioning solutions from Trimble to devise a plan of attack.”
Lou Nash, manager for Measutronics, explains that Manson required positioning guidance for its excavator as well as guidance for its tugboat and excavation barge, which was the platform the excavator worked from.
“We’d only recently done a similar project, having its own unique challenges,” says Nash. “But this second installation had quite a few more moving parts. The Manson guys are really sharp though and things came together relatively quickly as they overcame the learning curve.”
The team selected the Trimble GCS900 grade control system with real-time kinematic (RTK) positioning. The system uses a Trimble GNSS RTK base for global navigation satellite system (GNSS) corrections delivered over UHF radio. The grade control system includes the in-cab display, surface viewing screens, GNSS receivers, pitch and roll sensors, Wi-Fi network as well as angle sensors on the boom, stick and bucket. The excavation barge was outfitted with an RTK GNSS heading bundle, inertial motion unit and a commercial Wi-Fi connection.
“At the heart of the system was the excavator and Trimble sensors,” says Quiñones. “We wanted to have RTK-quality measurement of the bucket movements right down to the teeth-level in real-time. The system Measutronics helped us put together worked because it was equally effective in placing rock and removing material with a high degree of accuracy and reliability in very rough conditions.”
The sonar system included Trimble Marine Construction (TMC) software combined with USA-based Teledyne BlueView’s MotionScan system. MotionScan is a system comprised of Teledyne Blueview 1350 sonar, pan and tilt and motion compensation. Together, these systems stitch together an accurate picture of the river floor and the excavation work going on under the water’s surface. The system shows the operator the actual versus planned surface in 3D or profile view, and displays the excavator bucket, design depths and colour-coded digital terrain model in real-time. With all the equipment submerged, the system displays visuals that show the operator precisely how work is going – without it he would be working blind.
Quiñones explains that the sonar system was later mounted on a small shallow-draft boat to expand the coverage of survey data in shallow water. This required the use of an inertial navigation unit. The team leveraged a Trimble GNSS and inertial navigation system to remove the distortion of the sonar image caused by the movement of the boat. The sonar sweeps the area in front of the excavator, the data is then processed and loaded into the system so the operator can “see” what is in front of him. Quiñones believes the sonar scanning and positioning data were essential in ensuring the subsurface preparation was complete before moving ahead to avoid having to rework areas.
With the Wi-Fi connection, the operator and an engineer monitored the tug’s position, subsurface cut/fill progress relative to grade, and multibeam sonar data continuously throughout the day. This information provided the operator and project management personnel with a comprehensive view of how much material had to be excavated and how much fill was needed to meet the required tolerances.
“Every time the bucket went underwater and either took material out or placed material in, the system updated the model that was right in front of the operator,” says Quiñones. “Having all of that information flowing through our network allowed us to closely monitor our production from a variety of locations.”
Nash says that these sonar as-builts collected, or “as-building” as he calls it, are essential for project monitoring and were key for the precise placement of the training wall foundation material over the course of the project. The team was able to quickly reach required tolerances and avoided over cutting and rework, which had the potential to cause more shifting of material, thus adding costs over time.
Nash believes the Mile Point project is one of first marine construction projects ever completed using Trimble positioning and software systems in this way; where Teledyne BlueView sonar feeds Trimble Marine Construction software in real-time for a complete 3D model of work as it is happening.
“If you just give the operator a number representing the depth of the bucket, he could not be very productive,” says Quiñones. “Give the same operator a real-time view of the exact orientation of the excavator, the geometry of the bucket (curled or open or anywhere in between) and the depth of teeth and then supplant all that information into a real-time 3D model that updates itself as it goes, that gives the operator the perspective to be very effective, indeed. That’s because he can virtually ‘see’ the work he’s doing below the surface. It’s hard to imagine doing this kind of advanced work without this equipment. It was a massive team effort, Trimble and Measutronics helped us get there.”