| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 103 === According to the numerical results of pile loading test performed on three soil profiles determined by soil boring logs obtained from the wind farm near Chan-Hua coast of western Taiwan, the E-E'' soil profile which gave the lowest bearing capcity of single pile was utilized as the representive profile for the subsequent analyses. This study investigates the bearing capacities and mechanical behaviors of pile foundation installed on the seabed of wind farm near Chan-Hua coast of western Taiwan for the supporting structure of offshore wind turbine by three-dimensional (3-D) finite element program Plaxis 3-D.
Firstly, using the boring logs, SPT-N values, and laboratory tests of undisturbed sampes from the wind farm, one can estimate the required material model paramters of soil strata for numerical model. In addition, consulting the commonly used interanational design criteria and recent case histories, one can preliminarily determine the combined design loading and pile geometries which is appropriate for the environments of wind farm selected for the installation of offshore turbine. Secondly, numerical analyses were performed on two lateral loading tests of single model pile in laboratory and the comparisons between the simulation and measurement of the tests were made to calibrate the required soil/pile material model parameters. The comparisons show that the simulations of H~h curves (lateral loading H vs. lateral displacement h), lateral displacement, and bending moment distribution of pile shaft are in excellent agreement with the measurements. In addition, the numerical results indicate the utilizatons of Mohr-Coulumn soil model and embedded pile structural element enable a satisfactory simulation of the soil/pile interaction behaviors when subjected to lateral loading.
Subsequently, 3-D numerical models of single pile and pile group foundations for offshore turbine were constructed to simulate the soil/pile interaction behaviors subjected to various combined loadings. In numerical model, various pile diameter D, pile length L, and pile spacing S were selected as design parameters to inspect their effects on the bearing capacities and deformation behaviors of pile foundations. For different design parameters, which includes five pile diameters (D=1.0, 1.5, 2.0, 2.5, and 3.0 m), three pile lengths (L=30, 40, and 50 m), three pile spacings (S=12, 16, and 20 m), three pile length/pile diameter ratios (=L/D=15, 20, and 25), and three pile spacing ratios (R=S/D=6, 8, and 10), various loading~displacement curves, ultimate bearing capacities, ultimate bearing capcity envelopes on the V-H (Vertical-Horizontal combined loading ) plane, and the p-y curves can be determined under various combined loading conditions. In addition, a dynamic simulation was carried out on a pile group whne subjected to earthquake loading to inspect the soil/pile interaction responses. Finally, under the action of vertical, horizontal and bending moment combined loadings, a V-H-M 3-D ultimate bearing capacity envelopes can be determined and applied to evaluate the stability of pile foundation for offshore turbine when subjected to various working loads.
Based on the numerical results, several conclusions can be made: (1) Large displacement and plastic points at ultimate state mostly distribute and concentrate in the topsoil of seabed and around pile head. (2) The soil resistance at the soil/pile interface for lateral loading will ascend with the increases of depth, pile diameter and pile length. The gradient of p-y curve and ultimate bearing capacity for pile group is obviously higher than that of single pile. (3) The vertical, horizontal, and bending moment bearing capacities of sigle pile and pile group will be largely promoted with the increase of pile diameter. (4) For single pile, the vertical bearing capacity will be promoted notably with the increasing pile length. On the other hand, for pile group, the vertical and bending moment bearing capacities will be greatly promoted with the increasing pile length whereas the horizontal bearing capacity is almost insensitive to the pile length. (5) The influencial extent of spacing on the various bearing capacities of pile group from high to low in sequence is: bending moment loading horiztonal loading > vertical loading. Especialy, the bending moment bearing capacity of pile group is highly influenced by the pile spacing. (6) For different design parameters, the shapes of ultimate bearing capacity envelopes of pile group on V-H plane is similar while the envelopes will expand as the magnitude of design parameter increases. (7) For different loading levels of bending moment, the ultimate bearing capacity envelopes on V-H plane will contract as the bending moment loading gradually increase. In addition, when the bending moment loading reachs ultimate value, namely, M=Mult, the ultimate bearing capacity envelopes on V-H plane will contract into the origin of V-H-M space or coordinate system (0,0). (8) For the Vult-Hult-Mult (or V-H-M) 3-D ultimate bearing capacity envelope surface (or ultimate bearing capacity space), the pile foundation situates in a stable state if the coordinate of combined loading (V, H, M) falls inside the envelope surface. Further, the pile foundation situates in a critical state if the coordinate of combined loading falls on the envelope surface. Eventually, the pile foundation fails if the coordinate of combined loading falls outside the envelope surface.
|
|---|
