Protection From High Underwater Pressure, Noises and Vibrations

Protection from high underwater pressure and vibrations

Construction work was being done for Fincantieri Marinette Marine in 2021 in the Menominee River, USA, adjacent to the shipyard. This operation was made necessary to allow passage of larger vessels, which was required by the US Navy. Large sections of bedrock needed to be removed by the use of explosives underwater. A bubble curtain was requested to perform the following tasks: turbidity mitigation, fish deterrence, and to attenuate the blasts’ pressures during fish spawning season. Blasting underwater creates multiple issues for marine construction, namely high underwater pressure (PSI) and exceedingly high bursts of sound (dB). It was very important for authorities to lower and minimize any of those risks before they were carried out. In the case of this client underwater blasting project, high underwater pressure and ground vibration were found to be potentially harmful to marine wildlife, equipment, vessels and buildings near the site, as well as disturbances to nearby residents.

How does a bubble curtain work?

The use of Bubble Tubing® industrial air diffusers immersed in water at critical distances creates an efficient bubble curtain which buffers and acts as a sound and pressure barrier. Bubble curtains can attenuate the transmission and intensity of underwater noise, comparatively to how earmuffs would protect hearing from loud noises. Strategically positioned, these bubble curtains can attenuate various shock waves that are created by underwater activity such as pile driving, dredging, underwater explosions, rock blasting or drilling for oil exploration.  Bubble curtains will allow the free passage of vessels during construction and prevent marine wildlife from becoming entrapped inside a closed construction site, enabling them to leave the area towards a safe zone, even at the last minute.  Bubble curtains are a sensible solution for the environment.

Products Used

A complete custom system was required for this project. This system required two doubled curtains for a total of four (4) lines of industrial Bubble Tubing® that were installed at a specific distance surrounding the blasting area.

Bubble Tubing® is a third-party certified, industrial linear air diffuser typically used for aeration, de-icing and bubble curtains. It is designed and manufactured in Canada to our highest standards and specifications.

Air bubble diffusers such as Bubble Tubing® produce a large homogeneous dispersion of small air bubbles which are typically between one (1) and three (3) mm in diameter.  These precise bubble sizes and density ensure that coalescence is avoided and that an even distribution of bubbles will rise from the bottom to the surface of waterways, rivers, lakes or reservoirs to act as curtains.

Controlled compressed air enters the network of bubble curtains through manifolds with flow meters and safety features to create the expected results that contractors are searching to meet environmental requirements.  The nature of the Bubble Tubing® prevents it from clogging or fouling, which is typically found in porous hose or competing diffusers.

The Result

Roen Salvage Company, an experienced marine contractor, was able to register underwater pressure readings on explosions using transducers. Units were placed inside and outside of the bubble curtains at varied distances from the blast. The transducers were able to measure the impact, which was then calculated by their engineers to quantify the reduction of underwater pressure the Bubble Tubing® curtain achieved. While exploring various configurations, multiple readings were recorded using a 4-layer curtain and some with a 2-layer curtain.

Without the Bubble Tubing® curtain, readings of up to 295 PSI were recorded at 52 feet from the blast. This represents nearly 7.5 times the specification limit, which is known to be 40 psi maximum. After the installation of only one dual-line Bubble Tubing® System, the recorded pressure was 11.2 PSI. By testing and increasing the dual curtain to a four-curtain system, the pressure was further reduced to 5.9 PSI, which is well within the accepted range.

In a post-project damage assessment, it was concluded that by using Bubble Tubing® curtains, no damage was caused during the drilling and the underwater blasting.  Therefore, work was able to be carried out without damage within and outside the targeted site.  The various stakeholders were satisfied with the method and the marine contractor, as well as with Canadian Pond.ca Products and assistance.

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