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

直径相对较大的桩，特别是海上桩，经常受到大量循环的循环横向载荷。这导致不可逆位移的累积和桩头的永久旋转。这种永久旋转的预测是至关重要的，特别是在海上风能转换器的可移动基础的设计。对于单向载荷，可以进行相当准确的预测，而对于具有变化幅度的一般单向和双向载荷，不可能进行可靠的预测。从试验研究中得知，累积速率与荷载类型（用一个循环中最大和最小水平荷载的比值表示）的关系可用一个“荷载类型函数”来描述。通过一系列模型试验，本项目应阐明系统和荷载参数如何影响荷载类型功能。补充，小规模的模型试验计划，其中的过程中的沙子接近桩观察通过粒子图像测速（PIV）。该项目第1部分的结果（包括在中密细砂至中砂中对刚性和半柔性桩进行的试验）出乎意料地发现，所有研究系统的荷载类型函数在不对称双向荷载下具有相对较小的最大值，当荷载的杠杆臂发生变化时，该最大值也没有显著变化。在第2部分中，应阐明砂的相对密度变化如何影响结果，以及该功能是否取决于砂的类型。此外，还应研究非常灵活的桩土系统。项目结果应用于开发任意单向和双向荷载下位移累积的计算方法。

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.