A 1-g shaking table investigation on response of a micropile system to earthquake excitation

Considering the increasing applications of micropile systems in seismically active areas, a better understanding of their seismic performance and the key controlling factors is of high significance. This paper presents experimental investigations of the seismic performance of a small-scale physical model of micropiles under seismic ground motions. Shaking table tests were performed on a 4 × 4 group of vertical micropiles embedded in loose sand. Horizontal acceleration time histories recorded from the 1940 El Centro earthquake and 1995 Kobe earthquake were applied to the base of the soil container. The response of the physical model was monitored in terms of horizontal accelerations at different levels and bending moments induced in the micropiles. The experimental results indicate that in all shaking events, the magnitudes of horizontal accelerations on the soil surface and the pile cap were amplified with respect to the input motion. Bending moments were induced in the micropiles and peaked at the mid-depth. It was also found that inclining the micropiles led to improvement in their seismic performance, reducing both the acceleration response on soil surface and pile cap, and the induced bending moments in the micropiles. Finite element simulations of shaking table tests have been performed, and the results are in reasonable agreement with observations from the experiments.