| dc.description.abstract | In this study, a model pile is used to perform the long-term cyclic axial load tests in saturated sands, and the behavior of the pile-soil interaction is observed. In order to simulate jacket foundation of offshore wind turbine is long-term subjected to the upper structure weight and periodic wave force. The long-term cyclic axial pressure and tension forces are behaved on the pile, causing differential settlement for pile foundation and slowly tilting of the bottom of wind turbine, affecting the stability of the fan system long-term operation.
Before the cyclic load test is performed, static ultimate compressive load test is carried out, and then gets static ultimate load P_u. Loading static load 1/3 Pu initially owing to considering the static loads safety factor of the offshore wind turbine equal to 3, before the one-way cyclic axial load test carried out. A total of 6 sets cyclic axial load are carried out, 3 sets are performed cyclic compression type, and other 3 sets performed cyclic tension type. Three sets cyclic axial load amplitudes are1/3Pu, 1/6Pu and 1/12Pu respectively, and the number of cyclic cycles are 10000, 10000 and 20,000, respectively.
When comparing with previous studies done by dry sands, these are performed cyclic axial load tests show some of same results. Long-term cyclic axial load tests show that the stiffness of pile head decreases obviously owing to large of axial amplitude. And the incremental rate of pile head displacement velocity faster when axial amplitude large.
Under the tension and compression load tests of the same amplitude, the residual displacement caused by the long-term cyclic axial load tests. When cyclic axial load tests in dry sands, the residual displacement are larger in condition that first pression then tension. In contrast, where tests in saturated sands, the residual displacement are larger under the first tension then pression conditions. | en_US |