Vibracore Information

Vibracoring is a technology and a technique for collecting core samples of underwater sediments and wetland soils. The attached core tube is driven into sediment by the force of gravity, enhanced by vibration energy. The vibrations cause a thin layer of material to mobilize along the inner and outer tube wall, reducing friction and easing penetration into the substrate. With coring, the liquid spaces in the matrix allow sediment grains to be displaced by the vibrating tube. Vibracoring works best on unconsolidated, heterogeneous sediments and soils.

 

Pneumatic Vibracorer
Some of the earliest designed vibracorers came from the construction industry using impact hammers and vibratory motors to run pile drivers. Most of these tools were run by large air compressor systems and used pneumatic motors. The benefit of the pneumatic vibracorer systems is that the motor does not need to be pressure sealed and the systems are very simple to build. In addition, very high impact vibration can be achieved with these systems although most do not achieve as high of VPM. The downside is that they require large specialized vessels to operate on and they are very loud both on the boat and in the water – which can be a major problem for marine mammals. These systems are also limited to shallower water with hose lines being very cumbersome for any deep-water applications.

 

Hydraulic Vibracorer
Similar to pneumatic coring, most hydraulic vibracorer systems came from the marine construction industry, particularly with the design of the hydraulic pile drivers and compactors now on the market. Hydraulic vibracorers are some of the most powerful hydraulic rigs because large offset weights can be run along with high frequency using the benefits of the hydraulic torque curve. Hydraulic vibrators are often used only in shallow water as the hydraulic hoses are cumbersome for deeper depths. That said, when vibracorers are used at very deep depths most systems revert to hydraulic as the fluid is not compressible and deep-water housings are unnecessary. Many deepwater ROV systems utilize hydraulic pumps which has popularized the design of using ROVs for powering deep coring rigs. Hydraulic systems have come under some criticism due to the risk of fluid leaks in sensitive environments.

 

Electric Vibracorer
Most of the modern vibracorer systems have gone to electric operation with the exception of deeper water and heavy offshore systems. Electric can be broken up into DC and AC systems with both having very different profiles.

The early AC systems were designed by a very famous Frenchman named Andrew Rossfelder who had a colorful past that included being a resistance fighter in WW2 and being arrested for trying to kill the French President Charles De Gaulle after his home country of Algeria was abandoned by France. Rossfelder went on to develop the early electric vibracorer systems which are still in use today. The larger benefits of the electric motor is that you can achieve portability with both high VPM and high force output. In addition, you have infinite control of both frequency and in some systems impact force which is key to working in mixed sediments with sands and clays. Another unique factor with electric systems is that the motors can be designed with a dual-axis allowing for two offset weights to be run on a single motor. This both helps direct the vibration force down while acting like a gyroscope which helps keep the power head vertical while driving underwater. The downside is that most systems are rated to less than 1000 feet due to pressure housings and electric cabling.

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