Real scale experiments on the wave-induced burial and mobilization of Unexploded Ordnance on the seafloor

As a result of armed conflicts, huge amounts of Unexploded Ordnance devices (UXO) and Discarded Munition Material (DMM) are expected to be located on the seafloor, especially in coastal regions. During Offshore Construction, strategical site monitoring and systematic remediation activities, the behaviour of such objects in waves and currents is of huge interest as potential mobilization of objects after a survey or clearance activity could change the situational picture again. From findings and reports it often is assumed that UXO and DMM tend to migrate over the seafloor for long distances. Here, anthropogenic effects like fishing or dredging activities are underestimated. More scientific approaches clearly show that mobilization and migration of UXO over long distances does not occur. However, theoretical analysis remain theories until they are proven by experiments. For this reason, three large representative objects were investigated under real scale wave conditions in the Delta Flume of Deltares. The objects represent real scale models of UXO found in the North Sea as well as academically shaped objects. All objects as well as the Flume Tank were intensively instrumented to measure the full environmental conditions as well as the behaviour of the objects. The sediment represents typical sand as found in the North Sea and the seabed morphology and soil conditions were closely monitored during the experiments. The experiments support the theoretical models that predict burial but no mobilization also under extreme wave conditions. • Laboratory Experiments with real size objects and waves were carried out. • The self-burial of UXO on a sandy seabed by waves occurs faster than the increasing waves can mobilize the UXO. • Mobilization of large UXO due to waves does not appear. • It is shown that the results in general can be applied in oceanic scales.