Experimental investigation of monopile in overconsolidated marine clay subjected to multiple cyclic lateral loading events

Abstract

Monopile foundations installed at an offshore site must withstand severe marine environments during their service life. Consequently, their long-term behaviors require careful estimation to ensure adequate safety. This paper details a program involving 1-g model tests on the monotonic and cyclic lateral behavior of a monopile installed in overconsolidated marine clay. Using a self-manufactured loading device, attempts were made to simulate the possible response of the monopile during the serviceability limit state. Experimental results indicate that the deformational response of the monopile, which behaves as shakedown when applied to higher load levels, heavily depends on the load level. However, despite the dominant influence of the load level, the variation in loading frequency could extend the accumulation process of the pile-head deformation sustained from the first hundred to over 1000 loading cycles. In addition, the cyclic regimes of the foundation secant stiffness are affected by the loading frequencies, exhibiting either pure softening or combined softening/stiffening. The feasibility of the available design criteria and empirical models to estimate deformation accumulation is also evaluated based on the proposed test results, indicating that reassessment of the available design methodology is needed to promote applications of the monopile foundation.