Experimental investigation into effects of slope and loading characteristics on cyclic laterally loaded monopile in sand

Offshore monopiles subjected to waves and wind-induced cyclic lateral loading have been frequently located in complex terrains, such as sloping ground, thus demonstrating quite complicated response characteristics. To this end, this study experimentally investigated the pile responses in the sloping ground under cyclic lateral loading, focusing on the effects of slope and loading characteristics (i.e., loading direction and loading pattern). The measured responses indicated that the slope effect should be particularly considered under downslope loading because it would further amplify the cyclic response of piles. This amplification is related to the slope angle and rarely depends on the loading pattern. In addition, the relative magnitude of ultimate lateral capacity Pu with the maximum cyclic load may determine the elastic and plastic shakedown of piles in sloping ground. The maximum accumulated displacement is sensitive to the cyclic loading ratio (CLR) instead of the static load ratio (SLR), while the bending moment is reversed. The secant stiffness increases with the number of cycles and is greater in the upslope loading case, while it is reversed for the hysteresis loop area. Both secant stiffness and the hysteresis loop area, however, are sensitive to CLR rather than SLR, and closely related.