Influence of the soil liquefaction on dynamic characteristics of a base-isolated structure investigated by the experimental method

In previous studies, the dynamic characteristics of a base-isolated structure on non-liquefied soil foundation have been investigated by some model tests. However, soil liquefaction can change the seismic responses of the base-isolated structure. In particular, due to the soil-structure interaction, the seismic-isolation layer of the structure is also bound to change the seismic responses of the pile foundation under the isolation layer, and then this also affect inversely the isolation performance of the isolated layer. However, this scientific problem has not been effectively studied. To investigate the seismic responses of a complex soil-pile-isolated structure interaction (SPISI) system after the soil foundation liquefied, a new shaking-table model test was designed. The test results were analyzed and compared with a series of previous model tests on isolated structures with different non-liquefied soil foundations. As results, after the soil foundation liquefied, severe swing responses of the isolated structure and pile cap were observed. Then, the seismic responses of the pile were also changed evidently by the SPISI and severely aggravated by the strong swing responses of the isolated structure. Meanwhile, the foundation liquefaction also significantly weakened the isolation performance of the lead-rubber bearing and even amplified the horizontal acceleration response of the isolated structure. Because of the above SPISI effects, the dynamic characteristics and response laws of the isolated structure on a liquefied soil foundation are not consistent with those of base-isolated structures on non-liquefied soil foundations. On the contrary, they are similar to those of a non-isolated structure on the general soil foundation.