Accumulation of lateral pile displacements under general one- and two-way cyclic loading - Part 2

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Piles of relatively large diameter and in particular offshore piles are often subject to cyclic lateral loads with a great number of cycles. This leads to an accumulation of irreversible displacements and a permanent rotation of the pile head. The prediction of such permanent rotations is crucial in particular in the design of monopile foundations of offshore wind energy converters. A fairly accurate prediction is possible for one-way loading, whereas for general one- and two-way loads with varying magnitude no reliable prediction is possible. It is known from experimental investigations that the dependence of the accumulation rate on the type of loading (represented by the ratio of maximum and minimum horizontal load in a cycle) can be described by a “loading type function”. By a series of model tests, the project shall clarify how the loading type function is affected by system and load parameters. Supplementary, small-scale model tests are planned, in which the processes in the sand close to the pile are observed by means of Particle Image Velocimetry (PIV). Result of Part 1 of the project, which comprised tests on rigid and semi-flexible piles in medium dense fine to medium sand, was unexpectedly that the loading type function for all investigated systems had a relatively small maximum value for asymmetric two-way-loading, which also did not vary significantly when the lever arm of the load was changed. In Part 2, it shall be clarified how a variation of the sand’s relative density affects the results and whether the function depends on the type of the sand. Additionally, a very flexible pile-soil system shall also be investigated. The project results shall be utilized for the development of a calculation approach for displacement accumulation under arbitrary one- and two-way loading.