The caisson, in and out of which the lock gates will slide, measures 80m long, 26m wide and 22m high. Over recent months it has been immersed centimetre by centimetre to the correct depth. The caisson was sunk into the ground using remote-controlled robotic arms to remove the underlying sand. The fully-automated process was monitored 24/7 using sensors, measuring instruments and cameras installed underneath the caisson. The next stage in the construction operation is filling the space beneath the caisson with concrete.

Work has been underway in IJmuiden since 2016 to construct the world's largest sea lock and in 2019, the inner lock head caisson - 80m long, 55m wide and 25m high - will be immersed into its final position using the same method. Once completed, the new lock will be 500m long, 70m wide and 18m deep.