Laterally cyclic loading of monopile in dense sand

In order to investigate the response from laterally cyclic loading of monopiles a large centrifuge tests series is ongoing at the Technical University of Denmark (DTU). This paper will present some of the tests carried out with a focus on the influence of accumulation of rotation when changing the loading conditions. In these tests the load conditions are controlled by two load characteristics, one controlling the level of the cyclic loading and one controlling the characteristic of the cyclic loading. The centrifuge tests were performed in dense dry sand on a pile with prototype dimensions as following: The diameter of the pile was d = 2 m, the penetration depth of the pile was L = 6 d = 12 m and a load eccentricity of e = 15 d = 30 m. The loading of the pile was performed with a load setup which applies the load on the monopile in a manner that corresponds to the load condition for a monopile used for wind turbine foundation. This is important in order to get the right failure mechanism in the sand. The load frame is controlled with a feedback system which enables force controlled load series. A total number of 8 tests have been carried. In all of the tests, the pile was loaded with 500 load controlled cycles and for the entire test series accumulation of rotation was seen.