Effects of groundwater level on the seismic responses of coral sand ground and superstructure by shaking table tests

The changes in groundwater level in coral islands are more common than those in inland areas. In this paper, a series of shaking table tests were performed to investigate the influence of the groundwater level on the seismic response of a coral sand foundation–superstructure system. The responses of excess pore pressure, acceleration, displacement and bending moment of the model structure were measured and analysed in detail. The results illustrate that owing to the rise in the groundwater level, the natural frequency of the coral ground drops, while the damping ratio increases; in addition, the rising groundwater level has a softening effect on the model ground. Moreover, the excess pore pressure ratios of coral sands increase with rising groundwater level, and the increase in the ratios significantly grows with increasing earthquake strength. The amplification factors of the soil–structure acceleration response decrease with the increase in the groundwater level, regardless of whether the ground motion is weak or strong. Furthermore, both the settlement and horizontal displacements of the model structure increase when the groundwater level rises. In terms of the bending moment, the rise in the groundwater level will reduce the response of the column bending moment irrespective of the earthquake strength.