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Case study – Aertssen Group

Case study – Aertssen Group

How EIVA enabled high-precision dredging of contaminated sediment during a remediation and salvage operation

'We are very satisfied with the support from EIVA, as they are truly always available and have been great at helping to find solutions tailored to our needs.'
Chief Surveyor Sven Goovaerts
Aertssen Group

Environmental dredging can be more challenging than most

Environmental dredging is some of the most demanding work that a dredging contractor can bid on. Alongside the need for precision when removing pay volume from the cut, the need for vertical accuracy in the environmental branch is amplified. Strict penalties are often imposed should the contractor cut beyond the design grade, or equally by leaving contaminated material behind. The dredging operation which took place at the heavily polluted Lobroekdok is one example where conditions challenged dredging specialists.

Lobroekdok is a part of the port of Antwerp, Belgium. Its shallow depth is roughly 2 metres, and the dock is 900 metres long and 140 metres wide. Contaminated sediment was to be removed as part of preparatory construction work for the Oosterweel Link – a tunnel to replace the Antwerp Ring overpass. Once the clean-up operation was complete, the construction of the tunnel could begin.

clamshell bucket dredging contaminated sediment

The clamshell bucket bringing up contaminated sediment from the bottom of Lobroekdok

The contract stipulated that the contaminated sludge should be excavated to the clay layer, and consequently 220,000 cubic metres of material removed. The removal should be done with a vertical accuracy of 5 centimetres to preserve the vertical clay barrier laying underneath. Moreover, certain areas were affected by different grades of contamination. The different grades of contaminated material were to be mixed afterward in order to achieve a medium level contamination overall.

The Aertssen Group, an international Belgium-based family business with more than 60 years of experience in earthmoving and infrastructure works, won the contract at Lobroekdok. Their task was to carry out remediation and salvage works to remove contaminated sludge and unwanted objects from the dock. The operation began in August 2017 and ended in August 2019.

Software dredges up a solution

To achieve the high precision necessary, Aertssen Group employed additional software to their dredging setup: NaviSuite Uca – a 3D monitoring software bundle which features several tools dedicated to efficient dredging operations.

Dredger in NaviSuite Uca clamshell sensors

Sensors fitted to the excavator, boom, stick and clamshell bucket fed data to NaviSuite Uca software for real-time positioning

The dredging was carried out with an excavator stationed on a floating spud barge and equipped with a rotating hydraulic clamshell bucket. The excavator was fitted with positioning sensors so that all movements of the excavator itself, as well as boom, stick and clamshell, were interfaced and tracked with the NaviSuite Uca software. Furthermore, the barge and excavator were positioned with high-accuracy RTK GPS receivers.

Before dredging commenced, the site was surveyed with a multi-beam sonar to create a digital terrain model (DTM) of the environment at the bottom of Lobroekdok. The location of the barge spuds could be visualised on top of the DTM in NaviSuite Uca and used to avoid collisions with underwater obstacles. The exact dimensions of the clamshell bucket were imported as a 3DS drawing to represent actual position and depth within the software visualisation.

excavator cab visualising with NaviSuite Uca

In the cab of the excavator – real-time visualisation of the dredger, and the terrain and clamshell bucket under the water

eTrac rotation and open/close sensors were mounted directly onto the clamshell to visualise the exact XYZ position of the clamshell bucket during the dredge. Thus, enabling the clamshell bucket to be positioned at the correct height before each cut when opening and closing.

Following the setup and calibration, the operator began dredging with both the design grade model and the DTM loaded into the NaviSuite Uca software. The DTM updated in real-time, showing where sediment had already been removed and how much was left above the design grade, making the scene under the water highly visual and clear for the operator. The continually updating DTM in the software allows the operator to see the progress made each time the dredge surface is broken.

The contaminated sludge and unwanted objects were removed and discharged via vessels along the waterway. A silt curtain was placed in the passage of the dock which ensured the smaller particles did not pass to the Albert Canal during the operation.

Monitoring and calculating volume and progress

The project was divided into campaigns lasting 1-2 months. After each campaign a new multi-beam survey was conducted to confirm the accuracy of the operation and verify the removed volumes where it could be directly calculated.

Even with the visual assistance and real-time DTM provided by the software, there is no guarantee that the operator would not accidentally cut beyond the design grade. Therefore, as the clamshell reaches the design grade, NaviSuite Uca sends an alarm to the operator which potentially helps prevents an over-dredge.

NaviSuite Uca can calculate the dredged volume against the planned grade and generate a report in just minutes, which allowed the operations manager on shore to monitor the operation throughout, as updated volume reports were automatically sent through a Wi-Fi connection.

Dredging with NaviSuite Uca and removing contaminated sediment via a barge at Lobroekdok

Dredging to 5 centimetres accuracy and removing contaminated sediment via a barge along the waterway

The results of a real-time dredging monitoring system

NaviSuite Uca enabled Aertssen Group to successfully dredge Lobroekdok with the 5 centimetre vertical accuracy required to keep the clay barrier intact. During the length of the project, Aertssen Group removed 220,000 cubic metres of contaminated sludge, 17 shipwrecks and various industrial waste – among which were anchors, safes, mopeds, cans and refrigerators.

High-precision and efficient dredging were achieved thanks to the continuous updating of the DTM and the real-time 3D monitoring of the dredge site. In addition, the warning system enabled operators to adhere to tolerances and avoid breaking the vertical clay barrier bordering the design grade, therefore preventing costly penalties.

It was noted by Aertssen Group that they were able to control the operation in 3D on a 15” monitor, which gave them a better overview than the smaller display they used before.

After the successful dredging of Lobroekdok, Aertssen Group moved on to the nearby Kanaaldok B2 project where they continued to dredge with NaviSuite Uca. EIVA continues to support Aertssen Group in their dredging operations, such as with the integration, positioning and visualisation of a suction pump and milling drum attachment

Products in play

  • NaviSuite Uca
  • Custom software development
    • NaviSuite features and tools were made-to-order by EIVA – now integrated into NaviSuite Uca

Facts and figures

  • Lobroekdok is a part of the port of Antwerp, Belgium and a part of the moat of the Brialmont wall, dating back to 1859
  • The dock is 900 metres long and 140 metres wide with a shallow depth of roughly 2 metres
  • 220,000 m3 of contaminated sludge were removed
  • 17 shipwrecks, some partially and others fully submerged, were removed and recycled in a demolition yard in Hoboken
  • Anchors, safes, mopeds, cans and refrigerators were among the landfill waste found on the bottom
  • 5 centimetres of vertical accuracy was required during the sediment’s removal
  • A silt curtain was placed in the passage of the dock to ensure particles did not pass to the Albert Canal
  • Ten thousand trucks were kept off the road by removing and discharging material with vessels
  • The total clean-up of the dock took 18 months
  • The cost of preparing the dock for the Oosterweel Link amounts to 3.1 million EUR

Watch NaviSuite Uca in action in our dredging playlist on YouTube.

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