Elia Asset NV wanted to build a Modular Offshore Grid to connect four planned offshore wind farms to the onshore grid connection point at Zeebrugge. Boskalis Hirdes was called in to clear the unexploded ordnance (UXO) ahead of the construction of the subsea power infrastructure required for offshore renewable energy generation.
Elia tasked Boskalis Hirdes with the identification of potential UXO (pUXO) on the Final Master Target List, as well as the removal of non-UXO and the handover of UXO for disposal, prior to the installation of the submarine cables for the MOG project. Confirmed non-UXO was to be recovered and disposed; confirmed UXO was to be disposed by the Belgian Navy.
Kicking off in June 2018, the Boskalis operations ran from the beach area to nearshore and offshore with a wide range of equipment being deployed. Beach equipment consisted of a combination of a CAT345 excavator with UXO protection, together with a team using hand-held detection and survey equipment. For all target locations, the excavator excavated a layer of sand to allow deeper investigation, until the required depth was reached or the UXO was found. As a result, six pUXO targets were identified and cleared on the beach area.
For the nearshore, the Stemat 77 spud-moored barge was mobilized, handled by Boskalis’ multicat Yvonne. Divers were able to identify and clear 21 pUXO targets.
Furthermore, targets nearshore at water depths between 5 m and 17 m were investigated using backhoe dredger Manu Pekka (equipped with the Swiss Knife 2.58). The excavator of the Manu Pekka was fitted with several UXO identification devices, enabling operations in areas where Remotely Operated Underwater Vehicles (ROVs) experience a lot of downtime due to high tidal currents and low visibility.
The electro-magnetic detector TSS-440 was used to determine the target location and the DOP submersible dredge pump proceeded to excavate around buried objects. All the while, the ARIS Sonar Camera provided extra vision in the very turbid waters.
Once the non-UXO was confirmed, the grab was used to recover the object. All in all, 191 pUXO targets were identified and cleared by Manu Pekka.
Offshore, the work revolved around Boskalis owned and operated RSV Smit Kamara with its HD Schilling Work Class Remotely Operated Vehicle (WROV). The WROV was equipped with a TSS-440 electro-magnetic detector, a hydraulic-driven four-inch dredge pump and an ARIS sonar imaging camera. Targets in the deep-water areas were investigated using the WROV and the TSS-440 was used to determine the exact target location. The pump and ARIS camera were used for further investigation.
Confirmed non-UXO was recovered onto the vessel deck; larger objects were scooped up by the vessel’s crane and a grab. A total of 96 pUXO targets were identified and cleared.
After five months of action, the EOD operations were successfully completed.
Project execution: June to October 2018
