Abstract: A cyclic loading device was designed suitable for laboratory model test. The device, consisting of the motion system, driving system and reaction frame system, has the advantages of stability, low cost in manufacturing, adjustable load frequency and alterable amplitude of loads. The cyclic loading device is used to investigate the dynamic response and cyclic behavior of monopiles installed in the laboratory test box. The test results indicate that the similarity between measured load and theoretical load is about 91.3%, indicating that the load exported from the device is very stable and accurate. The accumulated deformation of monopiles in the soft clay increases at the beginning then gradually tends to be stable. Soil behind the pile is separated from monopiles and the cracks are formed in the surface soil surrounding the pile. The maximum moment along monopiles increases with the number of cyclic loads at the beginning, then tends to be stable after about 1 000 cyclic loads. The location of maximum moment of monopiles is about 4-5 times of pile diameter under mudline. It shows that the design of the loading device is rational, and suitable and reliable for the model test.

Key words: cyclic loading device, laboratory test, monopiles, accumulated deformation