Model tests of modified suction caissons in marine sand under monotonic lateral combined loading

•A novel type of suction caisson, i.e. MSC, is proposed.•MSC provides increased the lateral bearing capacity and reduces the deflection compared with the regular caisson.•The rotation center of the MSC varies with the loading condition.•Rotation centers of various MSCs are located at the depth of about 0.5–0.7 times the internal skirt length.•The range of sand deformation around the MSC is related to the external skirted structure and load eccentricities.

This paper presents a novel type of offshore foundation, a modified suction caisson (MSC), consisting of an internal caisson in an external short-skirted structure. A series of small-scale model tests were conducted to investigate the lateral bearing capacity of the MSC embedded in saturated marine fine sand. The lateral loading was carried out on the MSC at load eccentricity ratios of 1.0, 1.5, 2.0 and 2.5. Experimental results show that the MSC significantly increases the lateral bearing capacity and reduces the lateral deflection, compared to its corresponding conventional suction caisson. Parametric studies indicate that the bearing capacity of the MSC increases with increasing the external skirted structure dimension and the internal caisson aspect ratio, while decreases with increasing the load eccentricity. The lateral deflection decreases when the size of the external skirted structure increases. It was also found that rotation center of the MSC moves with loading conditions and the variation in the external skirted structure dimension. In the limit state, the rotation center is located at a depth of about 0.5–0.7 length of the internal caisson and is 0.15 diameter of the internal caisson away from its centerline.