Vibrocoring As An Effective Combined Geotechnical, Geochemical And Ass Investigation Tool

Vibrocoring has been conventionally conducted by many practitioners using aluminium tube of 50 mm to 80 mm diameter, requiring multiple holes to achieve ‘combined’ investigation sampling targets. Apart from the vibrocorer head itself, the penetration of the vibrocore tubes can be limited by the strength and diameter of the tubes, as well as the ability of the tube cross-section to effectively transmit the vibration energy. The length of the sample tubes is typically limited to a 6 m ‘standard’. GHD has worked together with MDS on a variety of projects, using 100 mm diameter steel vibrocoring tubes, to penetrate up to 9 m depth, through sands of up to medium dense/dense relative density and has been able to penetrate into stiff/very stiff clays for up to approximately 1 m (below other sediments). The use of steel tubes allows penetration where aluminium tubes will buckle, it also provides a more effective transfer of vibration energy (less damped) than for aluminium tubes and the wider diameter makes the sample significantly less prone to jamming on shells or blocking within coarser sediments, which effectively stops further penetration/sample collection. A number of case studies are presented, where geochemical, geotechnical and Acid Sulphate Soils (ASS) samples have been obtained from the same core, and where sophisticated geotechnical tests, including staged triaxial with pore pressure measurement, were possible on the firm to very stiff cohesive materials recovered.