A novel torsional test system for centrifugal modelling of interaction between finned suction caisson and soil

Suction caissons have been used in floating offshore wind farms worldwide with new types of finned suction caissons emerging to resist torque-loading. The additional fins attached to the caisson are expected to improve the torque-bearing performance, but the mechanism is yet to be clarified. Therefore, a novel torsional centrifugal modelling test system is developed to investigate the interaction between finned caisson and soil. The system is composed of the interacting chamber, the loading module, the transmitting module, and the measuring module. It allows precise control of the suction caisson penetration and pure torsional loading, which is validated by two torsion tests on a traditional caisson and a finned caisson. The results show that the torque-bearing capacity of the finned caisson is about 9.7 times that of the traditional caisson. The existence of the fins changes the failure mode from the interfacial friction failure between the caisson and the soil to the global soil-soil shear failure. The development of pore water pressure in soil was significantly changed by fins during torsional loading. The sudden change in the pore water pressure and soil pressure on the rear side of the fins indicates that tension gaps can be produced. The test results indicate that the developed test system is capable of evaluating the torsional performance considering foundation-soil interaction effectively.