Screw piles (helical piles) have been used widely as foundations for onshore projects due to their ability to provide high compressive and tensile resistance as well as reduced noise/vibration during installation. These types of piles have been proposed as a potential innovative foundation for offshore wind turbines in deeper water. In order to adopt the screw pile technique as an offshore foundation, the geometry of the piles would need to be scaled up so they can provide the high capacities required for this application. Such a change in size and geometry will lead to uncertainties in predicting the required torque for installation in different soil types and stress histories. Without the ability to accurately predict installation torque it is difficult to design screw piles for offshore use or develop appropriate installation plant with the required torque capabilities in different soils. This paper presents centrifuge test results of screw piles and CPT tests undertaken in dense sand. The installation torque (T) has been correlated to the cone resistance qc to establish a proposed CPT-based design method to predict the required installation torque for modified screw pile geometries.

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Cable ploughing is an important technique for burying and protecting offshore cables. The ability to predict the required tow force and plough performance is essential to allow vessel selection and project programming. Existing tow force models require calibration against full-scale field testing to determine empirical parameters, which may hinder their use. In this study the factors controlling the plough resistance were investigated using a series of dry and saturated 1/50^th scale model cable plough tests in sand in a geotechnical centrifuge at 50g at a range of target trench depths, sand relative densities and plough velocities. An improved model for predicting cable plough tow force which separates out the key components of resistance and allows tow force prediction without the use of field-derived empirical coefficients is presented. It is demonstrated that the key parameters in this model can be easily determined from in-situ Cone Penetration Testing (CPT), allowing it to be used offshore where site investigation techniques may be more limited compared to onshore locations. The model is validated against the centrifuge cable plough tests, demonstrating it can correctly predict both the static (dry) and rate effect (saturated) tow forces.