Experimental study on lateral behaviour of tetrapod caisson foundations in silt

This paper presents a programme of model tests on the lateral behaviour of tetrapod caisson-founded jacket (TCJ) structures in silt. Loading tests on the TCJ as well as on a mono-caisson were conducted at different rates. In addition to the load–displacement response of the TCJ, the vertical, horizontal and overturning forces at the top of the corner caissons were also measured by in-house-designed load cells. For monotonic loading, the resisting moment provided by corner caissons takes up only 8.7% of the total overturning moment acting on the TCJ. The bearing capacity of the TCJ accounting for caisson skirt friction (H_c) is 154% greater than when assessed without considering it (H₀) and, more importantly, the inclination needed in mobilising H_c is still within the allowable limit. For cyclic loading, simultaneous upward, excessive rotation of the jacket is developed when the maximum load amplitude (H_max) exceeds H_c. Cyclic loading with the minimum load amplitude (H_min) below H₀ proves to be desirable for the control of accumulative rotation, due to the essentially two-way loading characteristics of upwind caissons.