The monopile foundation concept is often employed as the foundation for offshore wind turbines. Typically, piles with diameters of 4-6 m and embedded lengths of 15-30 m are em¬ployed. Hence, the length to diameter ratio is around 5. The design method recommended by the American Petroleum Institute and Det Norske Veritas is, however, based on slender piles with length to diameter ratios larger than 10. Hence, the design method needs to be validated for non-slender piles. The aim of the present work is to investigate the pile behaviour for non-slender piles by means of small-scale testing. When conducting small-scale tests the low effective stresses in the soil is one of the major un-certainties. At low stresses the soil parameters will vary greatly with depth and the determination of soil parameters is therefore subject to uncertainties. This problem can be overcome by in¬creasing the effective stresses in the soil. A new and innovative test setup for small-scale tests is presented. Tests were successfully carried out in a pressure tank enabling the possibility of ho¬mogeneously increasing the effective stresses. The test setup is described in detail in the paper. A total of 29 quasi-static tests were conducted on six piles with diameters between 40 and 100 mm and length to diameter ratios of 3-6 m. The effect of applying an overburden pressure is eval¬uated for the load-displacement relationships and the variation of pile deflection with depth.
Ngm 2012 Proceedings: Proceedings of the 16th Nordic Geotechnical Meeting, 2012, p. 443-450