Characterisation of acoustic fields generated by UXO removal phase 5 quarry trials of bubble curtain mitigation

This report describes part 1 of the work undertaken in the project Characterisation of acoustic fields generated by UXO removal - Phase 5. The aim was to investigate the effectiveness of small bubble curtains used as a barrier mitigation for the acoustic output from UXO during low-order disposal by conducting controlled experimental trials in a quarry facility. This work was funded by the UK Government’s Department for Business, Energy and Industrial Strategy (BEIS) through the Offshore Energy Strategic Environmental Assessment programme (OESEA), Sub-Contract OESEA-22-142.
A total of nine explosive tests were undertaken during a two-day trial at the Limehillock Quary test facility in order to assess the attenuation of bubble curtain on the acoustic signal generated by underwater explosions. Three charge sizes were used of 45 g, 250 g and 465 g respectively, these being typical values in the range of charge sizes used on low-order techniques such as deflagration. Three air flow rates were used to generate a two-layer bubble curtain, with results presented for flows of 4.2 m3/min, 2.1 m3/min and no flow (no bubble curtain).
The results demonstrate that, under the conditions of the experimental trial, the bubble curtains can achieve a reduction in peak sound pressure level of between 13 dB and 17 dB, and in Sound Exposure Level of between 7 dB and 8 dB. The results show promise for use of a small bubble curtain to provide additional mitigation during low-order deflagration disposals, and suggest that further work may be justified to optimise the technique.