Vibracoring

Vibracoring is suited to rapid sampling of unconsolidated and semi-consolidated sediment sequences.  Unlike conventional rotary drilling techniques, vibracoring uses a submersible, electrically powered, vibrating head attached to a rigid core barrel (typically aluminium, but can also use mild steel, stainless steel or PVC) that is driven into the seabed.

 

This technique becomes most efficient in water-saturated sediments by raising the pore-pressure and generating a thin-layer of liquefaction along the wall of the core tube.  A bit/core catcher is attached to the end of the core barrel; it holds the sediment inside the barrel when the vibracore has reached maximum penetration or refusal and is withdrawn from the seabed.  The recovered barrel contains a continuous, undisturbed, in situ sample of the seabed substrate.

 

The entire coring process, including deployment and recovery of the drilling rig, is around 30 minutes depending on the water depth and deployment configuration.  The vibracore can be deployed and recovered in a number of different ways depending on the configuration of the drilling platform (e.g. A-frame, hydraulic crane, Hiab, etc).  Strong rope, strop or steel cable with a rated lifting capacity of a least 1 tonnes is required for the lifting of the vibracore from the vessel deck or from the seabed during deployment and recovery.

 

Upon recovery, core samples can be analysed on-site, or stored for later examination.  The core barrels can be cut to the length of the recovered core to enable capping and transport if required. Alternatively, the barrels can be cut lengthwise and split open to log, photograph and sample on-site.