Application of advanced in situ testing equipment and methodologies to characterise a low strength soil deposit in Sydney Harbour

In situ testing equipment and methodologies have evolved rapidly over the last 5 years. This paper looks at three devices that demonstrate this evolution: (1) a Special Purpose 3MPa CPTu Cone; (2) the automated Medusa flat plate dilatometer; and (3) the automated down-the-hole Vane Shear device. CPTu cones are now commercially available with special internal design and with capacities as low as 3MPa. These “special” cones, when carefully calibrated, are capable of reliably measuring CPTu parameters in soils right to the bottom end of the very soft range. The cones come with a temperature sensor to enable the management of potential inaccuracies associated with transient temperature effects during the penetration. The Medusa DMT, was developed by Marchetti to provide technicians and engineers with complete control and repeatability of the DMT diaphragm inflation and measurement process, eliminating many of the operator-dependant variables often encountered with the traditional gas-operated DMT. The Vane Shear Test is perhaps the most relied-upon geotechnical strength test; however traditionally it has had in-built potential errors, particularly in very soft soils, mainly due to ambiguity in friction corrections; it has been traditionally restricted to use in pure clay or clay-like soils. Equipment design has evolved (in some equipment) to eliminate the friction-correction problem. High quality calibration is required. These advanced in situ testing tools and improved methodologies were utilised in combination to characterise a low strength soil deposit in Sydney Harbour for a major infrastructure project. The results from the use of the advanced equipment and methods are discussed and reviewed in this paper.