Study on p-y Curve for Monopile under Cyclic Lateral Load in Soft Clay-Paper

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The study evaluates methods for predicting static and cyclic p–y curves for monopiles in soft clay, using samples from the Bohai Sea, China. Static and cyclic simple shear tests measured the clay’s stress–strain behavior, and finite-element analyses assessed whether p–y curves could be derived directly from these results.<br /><br />The direct-correlation method proposed by Zhang and Andersen, which scales soil stress–strain curves to obtain p–y curves, was found applicable to the Bohai Sea clay under static loading. Cyclic tests showed that the soil was vulnerable to repeated loading: specimens failed after 500 cycles at a shear-stress amplitude of 0.4 times the undrained shear strength, and after only four cycles at 0.6 times that strength. The resulting cyclic-strain contours differed substantially from those for Drammen Clay, highlighting the need for more tests to characterize local soils reliably.<br /><br />The study also examined how the equivalent number of cycles (Neq) varies along a pile. Beam-column analyses found that assigning the pile-head Neq uniformly along the pile gives a conservative, simplified prediction: in the example analyzed, it overestimated pile-head displacement by about 9% and maximum bending moment by about 6% compared with using the varying distribution. The authors therefore recommend calculating cyclic accumulation at the pile head alone for practical design, while noting that this approach is based on a specific loading case.

Keywords

monopiles

soft clay

p-y curves

static loading

cyclic loading

simple shear tests

finite-element analysis

Bohai Sea

equivalent number of cycles

pile-head displacement