Design of Large Diameter Monopiles under Lateral Loads in Normally to Moderately Overconsolidated Clay

摘要

The objective of this paper is to address the applicability of using API RP 2GEO (2011) for the designrnof wind turbine monopile foundations in normally to moderately overconsolidated clays. The studyrninvolved three-dimensional numerical modeling using the finite-element method, one-g laboratory modelrntesting, and analysis of field test results. The following conclusions concerning the use of Matlock (1970)rnsoft clay p-y curves for the design of large-diameter monopile foundations are drawn:rn1. Numerical modeling and model-scale testing with rigid piles of different diameters indicate thatrnthe form of the Matlock (1970) p-y curves, in which the lateral displacement is normalized by pilerndiameter and lateral soil resistance is normalized by the ultimate resistance, appropriately capturesrnthe effect of pile diameter.rn2. Field and model testing indicate that the Matlock (1970) p-y models consistently overestimate thernlateral displacements at the pile head when used to analyze laterally loaded piles in normally tornmoderately overconsolidated clays.rn3. An approximate version of the Jeanjean (2009) p-y model, in which the Matlock (1970) p-y curvesrnare scaled by p-multipliers calculated at various depths, generally provides a reasonable match tornmeasured lateral displacements at the pile head when a relatively large strain at one-half thernundrained shear strength is assumed, i.e., ε_(50)= 0.02. This result applies both to small scale modelrntests in kaolinite and large-scale field tests in high-plasticity clay.rn4. Model tests show that cyclic loading causes the stiffness of the lateral pile-soil response to degradernby 20 to 30 percent. The amount of degradation is dependent on the displacement amplitude andrnthe number of cycles. All of the degradation happens within 100 cycles, after which the stiffnessrnis reasonably constant.rn5. Model tests show that the ultimate lateral capacity of the pile is not significantly affected by thernprevious cyclic loading.