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.