CPT-based design procedure for installation torque prediction for screw piles installed in sand.

Abstract

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.