Dredgers - 3D Machine Control On the Water

Randy Noland

On a recent business trip to Europe, I visited Dredging International (DI) of Antwerp, Belgium. DI is one of the top four dredging companies in the world, with offices and projects that span the globe. My mission was to learn how 3D machine control is used in the world of dredging.  My DI contact, Peter De Moor, Survey Hardware Coordinator, gave me a crash course.

The first thing I learned was that dredging is indeed earth moving. It is very similar to land based grading applications we discuss here at MachineControlOnline, in that the process involves cutting where the earth is too high, and filling where the earth is to low,  moving and balancing the earth by whatever means necessary. The difference for dredging applications is that this occurs underwater - common sense, to be sure, but there is quite more to this as it relates to land-based earth moving.

Water ways and coast lines are ever changing; riverbeds, bays and ports accumulate sand, soil and debris and they must be dug out, i.e. dredged, to keep the shipping lanes open for commerce, etc. 

While there are several kinds of dredgers, I will use the example of a hopper dredger for a basic description of the workflow (See Fig. 1).  While dredging, a suction hopper dredger trails the ship, using suction pipes on the ocean floor like a giant vacuum cleaner. Sand from the seafloor is carefully loaded and balanced into several hoppers in the vessel. When the hoppers are full, the hopper dredger sails to the disposal area and dumps the material through the doors in the hull, or pumps the sand out of the hoppers. The pumping can be through a pipeline (Fig. 2) or by spray pumping or “rainbowing” (Fig 3).

Dredging benefits from positioning and 3D machine control technology both in cutting and placing material. “RTK GPS and machine control gave us the tools to make these vast man made islands where there are no straight lines longer then one meter.” says De Moor. “On our first job with machine control (The Pearl Qatar 2006 - Fig. 4) we used two machines with machine control; on the next one we did use seventeen machines equipped with 3D machine control.”

3D machine control is installed and applied in a typical manner. Strategic placement of various sensors such as accelerometers and precise GNSS facilitate monitoring and positioning of each machine’s particular articulations. Relevant data is displayed on a computer screen where the operator interfaces and commands the system, enabling real-time monitoring of the dredging progress (e.g. volumes) on the sea floor. This is similar to a dozer or excavator pushing dirt from a cut position, sculpting the cut towards the design elevation. 3D machine control technology is a welcome tool when compared to low-tech, time consuming traditional methods, such as involved putting long sticks in the water to mark new depths.

 

Precision GNSS is also used when rainbowing, allowing for exact positioning of extracted sand (the “fill” material). This ensures efficient material placement, reaching the desired design in the most accurate and economical way. Examples of land reclamation are managing eroded coastlines, building new shipping ports, or building new islands where there were none before. Well-known examples of the latter are the Palms and World Islands in Dubai and harbor extensions in Singapore

(Jurong 1,2,3,4) and Le Havre (Port 2000). DI did the work on the Pearl of the Gulf (Qatar and on Al Marian (Ras al Khaimah. See Fig. 5)Pearl of the Gulf, Qatar

The first step in construction of these islands first is to build a rock frame that traces the outline of the landform design. This is a huge task: many thousands of tons of rock are placed using precise GNSS. The dredged sand is then rainbowed, filling the area inside the rock frame. Water is pumped out as the sand begins to form reclaimed land. “In Ruwais we are reclaiming 42 million m³ of material. All will be compacted by means of machine controlled compactors which can be monitors from the office,” says Peter DeMoor. “Reclamation works where we need to reclaim more than 50 million m³ of material are no longer a problem for our dredgers, but we surely are going to need machine control to manage ashore.”

Cast of Equipment

To perform this work requires a diverse cast of heavy equipment (which may well be a gross understatment. DI's fleet is comprised of four types of dredgers: Click on type to get more detail.

  1. Cutter Dredger
  2. Hopper Dredger
  3. Backhoe Dredger (excavator on pontoon)
  4. Bucket Dredger (not unlike a bucket wheel excavator used in surface mining applications)

There is also a host of support equipment to round out the dredging process

  1. Multicats (small boat with enough space to put spare cutter on board, most of the time foreseen of a small hydraulic crane)
  2. Tug Boats
  3. Drilling Platforms
  4. Construction Boats
  5. Survey Boats (topography using GNSS and depth measurements)

Dredging and all of its supporting applications and equipment benefit greatly from 3D machine control, positioning and connectivity. The scale of these projects is incredible and constant analysis on how to improve productivity is an ongoing challenge. DI is at the forefront applying new technology to achieve these goals even inventing tools required to accomplish their tasks. “Creating land for the future” is their company mantra and this they do with passion, expertise and advanced technology. I would like to thank Peter DeMoor, his colleagues and DI for their cooperation in putting this article together for MachineControlOnline.

To learn more about Dredging International and DEME, click here

Update: See video shot while on a hopper dredger. Dredging in Belgium - click here.

-Randy Noland

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