Abstract
Helical (or screw) piles, sometimes defined as anchors, are a piled system consisting of one or multiple helices welded along the shaft. Piles are installed by applying a torque to the shaft. The pile is rotated into the soil and the rate of advancement should be an amount equal to the pitch for each rotation in order to minimize the disturbance of the original soil. Torque is maybe the most important parameter to be assessed during pile installation. In fact, torque and uplift capacity are directly proportional. Generally, torque depends on the soil conditions and on the geometrical features of the pile. Torque increases with sand density, installation depth, friction angle of sand, pile shaft and helix diameters. The geometry of the pile has a strong influence on the torque, the larger the helix-to-shaft ratio is, the larger the torque will be. In offshore applications helical piles are being considered as a valid alternative. However, one of the issues is still related to the assessment of the installation torque values. Several torque models have been considered and critical evaluated. Some simple comparisons among selected torque models have been also done and discussed.
Highlights
IntroductionBoth for oil & gas and renewable energies, driven and sometimes drilled piles are the most used foundation type [1,2,3]
For offshore structures, both for oil & gas and renewable energies, driven and sometimes drilled piles are the most used foundation type [1,2,3].In the offshore environment piles are often subjected to uplifting forces [4,5]
Many offshore structures require foundations-anchors with a significant tension capacity, such as tension-leg platforms [2], tension-leg floating wind turbines [6], wind turbines founded on tripod [7] or jacket [8] structures, converting moment at the base of the turbine into a push/pull loading applied to the foundations [9]
Summary
Both for oil & gas and renewable energies, driven and sometimes drilled piles are the most used foundation type [1,2,3]. Helical (screw) piles are a valid form of foundations and they have been successfully used in different ground conditions including marine environments [11,12]. They are installed into the soil by applying a torque to the upper end of the shaft by mechanical means [13]. Very important in offshore operations as it is directly dependent on the site condition, pile geometry and the design depth estimated for reaching the necessary load capacities (in tension and compression) [19,20]. This paper shows different torque models proposed in the past and calculation examples are performed considering a pile geometry and geotechnical conditions to show the different results obtained
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