Two of the most crucial sediment physical parameters controlling slope stability and trigger mechanism of mass movements are shear strength and excess pore pressure. Since both of them require in situ measurement, Cone Penetration Testing (CPT) is an ideal method to characterise in situ. While standard CPT tests penetrate of sediments at constant rate, a new free fall cone penetrometer (FF-CPT) for shallow-water application down to 200 m water depth has been developed. Its modular, lightweight design allows us to operate from small platforms to research vessels. The length (0.5 m – 6.5 m) and the weight (40 kg – 170 kg) of the device can be adapted according to the geological setting and main scientific interests. Here we present our initial results as a "proof-of-concept". In five locations with variable sediment composition, the lance was deployed with different penetration velocities ranging from 30 cm/s to free drop in different weight- and length-modi. Based on the primary data (acceleration, cone resistance, sleeve friction, pore pressure), we mainly focus on dissipation of insertion pore pressure and a first-order sediment classification. The results show an influence of the different penetration velocities on pore pressure regarding to its evolution over the time and on the magnitudal strength parameters. Finally, our preliminary data suggest that the time- and cost-effective use of our marine FF-CPT is an appropriate alternative to standard CPT measurements.
Initial Results of a new Free Fall-Cone Penetrometer (FF-CPT) for geotechnical in situ characterisation of soft marine sediments