Variation in axial load distribution of piles in liquefiable slope by centrifuge test. Issue 167 (April 2023) - Yoo, Byeong-Soo
Abstract: During seismic loading, the axial pile response is significantly affected, due to the development and dissipation of excess pore pressure in the foundation soil. Positive skin friction is reduced by liquefaction during shaking, while negative skin friction is caused by reconsolidation after the end of the shaking. In particular, the negative skin friction causes a large drag load, resulting in pile compression and settlement. Thus, this study investigated the axial pile response under seismic loading by performing dynamic centrifuge tests on liquefied sand with the slopes of 15° and 27°. The centrifuge tests were conducted to simulate the end-bearing single and 2 × 2 group piles embedded in a liquefied slope. During the centrifuge spinning, the obtained drag load due to the negative skin friction agreed with the value calculated with the beta method for shaft resistance. The model was shaken with sinusoidal base motion with peak amplitudes of 0.1 and 0.2 g, and it was found that the liquefaction caused a loss of spin-induced drag load. The dissipation of excess pore pressure resulted in reconsolidation settlement, leading to large drag loads acting on the pile. In addition, the negative skin friction was found to be larger than the liquefied residual strength recommended in the current practice codes. As a result, it is seen that the consideration of the strength reduction is not necessary for the calculation of negative skin friction induced by reconsolidation, since the liquefied ground regains skin friction after the dissipation. Highlights: Pile axial load disbribution before and after shaking was measured by centrifuge test. Ground settlement during centrifuge spinning induced negative skin friction. Spin-induced drag load linearly decreased with the increase in the excess pore pressure ratio. Post-liquefaction settlement induced negative skin friction corresponding to beta method.