Trimble Real-time 3D Surface Models Help Manson Construction Co. Accelerate Breakwater Build at Mile Point

Manson was awarded the contract for the excavation dredging and construction work for the Mile Point project in April 2015 from the U.S Army Corp of Engineers in Jacksonville Florida. Construction began in April 2016 and was completed in late 2016. 
Ken Quiñones survey engineering manager for Manson explains that the multi-phase $43.5 million project involves 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 proposed 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 said that the Mile Point project includes multiple phases that entail 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 requires 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.
The project was also 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.
During the bid process Manson chose to partner with Trimble and authorized dealer Measutronics Corporation to develop a solid technological approach to deal with the need of critical plant positioning and the use of specialized acoustic imaging in shallow water. 
“The Mile Point project was a complex job with many phases of work” Quiñones said. “From our perspective it required specialized machine guidance to accurately prepare the subgrade for where we would ultimately place the CSUs. With shifting tides and only 3 to 4 feet 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 said that Manson required positioning guidance for its excavator as well as guidance for its tug boat and excavation barge which served as a platform for the excavator.
“We’d only recently done a similar project having its own unique challenges” Nash said. “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” Quiñones said. “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 Teledyne’s BlueView MotionScan system. MotionScan is a system comprised of TBV 1350 sonar pan & 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 color-coded digital terrain model in real-time. 
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. He 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 sub surface cut/fill progress relative to grade and multi-beam 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.” Quiñones said. “Having all of that information flowing through our network allowed us to closely monitor our production from a variety of locations.”

The software collected motion-compensated 3D point clouds to create a 3D model from the moving barge platform in real-time.

Nash explains that these sonar as-builts collected or ‘as-building’ as he calls it are essential for project monitoring and 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. To date 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 (TMC) 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” Quiñones said. “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.”