Comparative assessment of differing in-situ degradation behaviour in offshore silt and sand soils using Cyclic and Dual Sleeve Piezocone Penetration Tests

Modified Piezocone Penetration Testing (CPTu) methods, including the Cyclic CPTu and Dual Sleeve CPTu, have been deployed in offshore geotechnical investigations to aid evaluation of in-situ soil characterisation. Both techniques involve large strain amplitude shearing of the soil element in contact with the CPTu tool which may provide additional useful information regarding the cyclic response of the soils in-situ. The behaviours thus characterised may prove valuable in design parameter derivation, prediction of suction bucket foundation installation / extraction resistance, and the static and cyclic capacity of these foundations. The authors detail the equipment and methods employed, and compare the results of CPTc and Dual Sleeve CPTu performed in differing soils. Observations are made about the characteristic behaviours encountered in these different materials, limitations of the methods observed in certain soils, the validity of the data in modelling real world foundation installation and loading conditions