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

Conference Proceedings OTC2015: Offshore Technology Conference, 4-7 May, Houston, Texas, USA, Paper OTC-26031-MS

04 May 2015
Senanayake, A.I., Rendon, E., Wang, S.T., Gerkus, H., Stevens, R.F. and Gilbert, R.B.
DOI: 10.4043/26031-MS

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


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