Rotary coring is a process by which a borehole is formed by rotary methods. The system uses a variety of rotating core barrels and cutting bits in conjunction with different flush media; the choice of which is dependent on the ground conditions encountered and the geotechnical information required.
Rotary coring is more commonly employed where the identity and character of the rock is required and allows for laboratory testing for strength and deformation properties. Examples of applications include examining the risk of punching failure on end-bearing piles or other geotechnical risks such as karst.
Coring can take place from ground level or the base of a cable percussive borehole and eliminates the risk of effective refusal in cable percussive boreholes. Simultaneous casing systems allow tube samples up to Class 1 to be retrieved as the hole is advanced. The core is brought to the surface for further analysis within the inner barrel using a wire rope or attached line to a recovery tool.
Field tests include the Standard Penetration Test (SPT) where a thick-walled sample tube or solid cone is driven into the ground by blows from a 63.5kg hammer over 300mm. The N-value offers an indication of soil strength, relative density and other parameter after some corrections are applied. On completion, a piezometer can be installed to monitor pore pressures.