Sea lock IJmuiden, IJmuiden, The Netherlands

The port of Amsterdam is protected by a closed sea defense to enable cargo transfer independent of current and tide. Due to expected increased throughput and increasingly larger vessels, a larger lock was required to enable future economic growth of the port. A new lock also provides maintenance possibilities for the existing crowded locks. The new lock is the world's largest, with dimensions of 500m length, 70m width and 18m deep.  

The works on the new lock have been dictated by the restricted available space and strict settlement restrictions due to the nearby sea lock in operation. These circumstances forced to come up with special techniques. For the two large underground structures to house the sliding gates, caissons have been developed. This building technique minimizes the risks of large building pits close to existing structures, and also the risk of vessel collision due to heavy shipping lanes. 

Two mighty concrete caissons have been build and lowered to their final foundation levels by removal of soil from the pressured chamber underneath the structures. Due to the size of the caissons and also the relatively vulnerable open structures, the operation had to be prepared to a very high level of detail. Both caissons have been successfully positioned in 2019 and 2020. The caissons house a total of three semi-flooding gates, each measuring 71m x 25m x 11m. Each steel gate contains valves for flooding the lock, in this way avoiding having to build large flooding channels round the lock. 

During normal circumstances, two of these gates are in operation and each serves as a primary sea defense.  The third gate is a spare one and may be required e.g. after a vessel collision. The spare gate can be installed and made operational within 24 hours after the incident. The retaining walls have been designed and built using mainly diaphragm walls. These can be installed without vibrations thus also close to the existing lock in operation.

DMC performed the tender, basic and detailed design for the concrete caissons, the retaining structures and temporary works. 


Port and Harbour Development, Coastal Engineering
Specialists Services
Civil & Structural Engineering, Coastal Engineering

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