Experimental study on the bearing capacity and failure mechanism of suction anchor in trenched seabed under cyclic loading

During the service life of a suction anchor, the alternating movement of mooring line causes seabed trenching in front, influencing the bearing capacity of the suction anchor. Previous studies on suction anchors in trenched seabed mainly focused on numerical simulations with monotonic loading. However, the failure mechanism of suction anchor is strongly related to the excess pore water pressure generated, which is expected to vary significantly under cyclic loading with different seabed conditions. Therefore, there remains a gap between previous research and practical applications. In this study, a series of laboratory model tests were conducted to investigate the combined effect of cyclic loading, seabed trenching, and stress history of surrounding soils on the bearing capacity and failure mechanism of the suction anchors. Results indicate that (a) the combined effect of trenching and cyclic loading reduces the capacity of the suction anchor, which is more significant in surrounding soils with higher preloading. In simulated normally consolidated seabed, the combined effects of cyclic loading and trenching can reduce bearing capacity to 58% of its initial value, while in soil with an 80 kPa preloading it is only 48% of initial value; (b) the trench changes the failure mechanism of the suction anchor, increasing the failure angle and shifting the rotation center; (c) higher preloading on surrounding soils enhances the cyclic bearing capacity of the anchor and reduces its failure angle in intact seabed. Besides, a new calculation method incorporating the combined effects of trenching and cyclic loading is proposed to predict the bearing capacity.