Lateral behavior of large-diameter monopiles in clay using transparent soil and centrifuge tests

The response characteristics of large-diameter monopiles under lateral loads greatly differ from those of traditional small-diameter piles. By means of transparent soil and centrifuge tests, as well as numerical analyses, the soil flow mechanism and lateral behavior of large-diameter monopiles in soft clay were investigated. The study result reveals that a rotational failure mechanism, different from wedge-full-flow mechanisms, exists in the large-diameter monopile–soil system. For stubby large-diameter monopiles, using the classic wedge-full-flow mechanisms can lead to an overestimation of lateral capability due to its absence in considering the rotational mechanism. In addition, the normalized p–y curves in the rotational soil flow zone are also observed to have larger initial stiffness and attain yield plateau earlier than those in wedge-full-flow zone. Differences in N_p values among different centrifuge tests are partly attributed to the different means of obtaining the clay’s undrained shear strength. When the undrained strength from consolidated undrained triaxial tests is taken, consistent values of N_p originating from different test results are observed. Finally, based on the results from centrifuge tests and well-calibrated numerical analyses, an empirical formulation of N_p for large-diameter monopiles in soft clay is proposed.