The foundations of power transmission towers and offshore wind turbines are prone to huge overturning moment loading from the super structure; therefore the overturning bearing capacity is crucial for the design of such foundations. To investigate the overturning bearing capacity of suction caisson foundation

four centrifuge model tests including a displacement controlled cyclic loading test

a displacement maintained loading test

a load controlled cyclic loading test and a monotonic loading test were carried out in saturated soft clay. The test results show that the instantaneous rotation center of model caisson can be simplified to be at the depth of about four fifths of the skirt length right below the lid center

when the ultimate capacity was reached. When the amplitude of the cyclic moment is smaller than three-fifths of the bearing capacity moment

the rotation of the caisson cease to accumulate

and gradually become stable. The stiffness of the soil-structure interaction significantly softened under cyclic loading

and a threshold of cyclic degradation factor t = 0.15 can be obtained from the peak stiffness curves of the caisson. The moment-rotation curve of peak value of maintaining tests is universally quite in accordance with that of monotonic loading test. The capacity of the model caisson corresponding to the moment-rotation curve of the valley values is much lower than that corresponding to the moment-rotation curve of the peak values in maintaining tests

and a 30%-40% reduction is needed when considering the maintaining overturning capacity of the caisson foundation in design.