Stiff monopiles are widely used for supporting offshore wind turbines. The p-y method recommended by API code is commonly used for the design of stiff monopiles, which was developed based on the test results of a small-diameter slender pile and would significantly underestimate both the stiffness and ultimate capacity of stiff monopiles. However, till now, no approved design method is available for stiff monopiles. To investigate the lateral behavior and failure mechanism of stiff monopiles in clay, 3D finite element analyses using an advanced hypoplastic clay model are performed. It is revealed that two distinct flow mechanisms (a wedge mechanism near the ground surface and rotational soil flow at depth) can be identified in the vertical symmetrical plane of the stiff monopile. Due to the different failure mechanisms from slender piles, the extracted p-y curves from the finite element analyses, are substantially stiffer than that recommended by API code at shallow depth and exhibited a bilinear distribution at depth. A new p-y model for stiff monopiles is proposed and validation shows that the model can satisfactorily predict the lateral response of stiff monopiles.
B. He, Y. Q. Lai, S. X. Zhao, W. Li, J. P. Luo and Z. Q. Jiang
Keywords: stiff monopile, FEM, hypoplastic clay model, p-y curve, failure mechanism
Publisher: DFI