Soon, the question arose whether the bottom of the Oosterschelde was prepared for the weight of the barrier. For that reason, the bottom was thoroughly investigated. The solidity and density of the foundation, the composition of the bottom, the bottom stratification and the geological structure of the layers were examined. The research showed that several adaptations should be made before the barrier could actually be constructed. The bottom on which the barrier would be placed, was revealed to be far too weak. Tests were conducted in laboratories, in order to examine what would happen to the bottom under certain circumstances.
Several operations were performed to consolidate the bottom. The ship Mytilus, for instance, placed vibration pipes into the bottom. After the vibration, the grains of sand were knocked closely to each other down to fifteen metres of depth. Synthetic mats were also put at the bottom around the location where the barrier would later be placed. Consequently, these mats were covered with concrete blocks. Next, the silt was dredged and replaced by sand. However, the bottom of the Oosterschelde was still too weak to carry the barrier. Because of that, special mats were made on the mainland, which would be fitted to the relevant section of the storm surge barrier. This mat was a kind of mattress, which was filled with sand and gravel, instead of springs.