The objective of this research is to develop and test a new method for the burial of surrogate unexploded ordnance (UXO) targets in marine sediments based on sediment fluidization. Fluidized sediments have no compressive or shear strength, and in this state targets can be lowered into the sediment with only buoyant and drag forces acting on them. Once the fluidization flow is stopped the sediment regains its natural state and emplaced targets will remain buried in place. Once developed, this technique can be used to build a ship operated bottom lander capable of burying targets to 0.5 m depth or more in marine sand and silt sediments quickly and with minimal operational limitations. With the integration of existing underwater navigation technology such a target burial system could provide accurate target burial position, depth, and orientation to test site operators.

Testing incrementally developed and validated methods to fluidize sediments from above, while descending through the fluidized area with a manipulator and target to be buried. Laboratory tests performed with commercially available sands defined operational parameters such as fluidization flow rates, burial rates, and jet sizes as a function of sediment grain size. Field tests validated the method in real world sediments.

During the project, a hydraulically operated manipulator capable of fluidizing seafloor sediment and handling surrogate UXO targets up to the size of 155 mm mortar shells was designed and built. The manipulator was integrated into a ship deployed bottom lander for field testing.

Laboratory tests showed that fine and medium grained sands can be fluidized by jetting water from above, and that broad-sided targets can easily be buried in the fluidized sediment. The combination of higher hydraulic conductivity and increased minimum fluidization velocity in larger grained sediments make fluidization of coarse-grained sands (laboratory tests were conducted in sand with mean grain diameter of 1.18 mm) impractical without restricting the radially outwards flow of water through the sediment with a coffer dam.

Field tests were conducted at three sites ranging from medium grained sand to mud. The system was able to successfully fluidize sediments and bury targets into the fluidized sediments up to 0.65 m deep. When fluidization flow was stopped, the targets remained buried. A dense shell layer at one test site could not be penetrated. Sediment core data at field test sites showed no significant change to the bulk grain size distribution due to fluidization and burial.

This limited scope project developed a new method for surrogate UXO and clutter target burial at demonstration sites, or for establishing calibration lines at real world UXO survey sites. This burial method can be developed into a surface operated bottom lander with low technical risk. Such a bottom lander would have minimal operational limitations compared to dive teams, be able to bury targets quickly, and provide accurate target burial position, depth, and orientation to test site operators.