Shaking table test of liquefaction resistance of group piles under strong earthquake

To study the specific manifestation of the improved basic liquefaction resistance of group pile foundation in comparison with that of single-pile foundation under strong earthquake, considering the Haiwen Bridge Project in Hainan Province as an example, a shaking table model test was adopted to examine the differences in foundations comprising one, four, and six piles. The differences in the time-history responses of pore pressure ratio in saturated fine sand, pile acceleration, and bending moment under three different working conditions, and their relationships were analyzed. The results indicate that the liquefaction occurs under all three working conditions and a ground motion of 0.35g. The time when the pore pressure ratio begins to increase and that when the ratio becomes stable in the deep layers of saturated fine sand lag behind those in the shallower layers. The time required for the complete liquefaction of the foundation with six piles is 4.41-4.82 s longer than that for the foundation with four piles. The time required for the complete liquefaction of the foundation with four piles is 4.00-4.42 s longer than that for the single-pile foundation. With more piles, the maximum pile acceleration and its amplification factor in the saturated fine sand at the same depth decrease gradually, and the maximum pile acceleration gradually lags behind. In addition, as the pore pressure ratio increases, the pile acceleration decreases gradually. The maximum bending moment of the foundation with six piles is 25.95%-43.50% smaller than that of the foundation with four piles. Similarly, the maximum bending moment of the latter is 28.80%-33.10% smaller than that of the single-pile foundation. The maximum bending moment of the single-pile foundation appears 1.22-1.27 s earlier than that of the foundation with four piles, whereas that of the latter appears 0.66-0.72 s earlier than that of the foundation with six piles. Furthermore, the bending moment of pile gradually attenuates as the pore pressure ratio increases, indicating that the saturated fine sand provides softening and damping effects before liquefaction. In summary, the liquefaction resistance of the foundation with six piles is better than those of the foundations with four piles and one pile. Thus, in the antiseismic design of pile foundations for liquefaction-prone soil layers, the liquefaction resistance of foundations can be improved by using group pile foundations. 10 tabs, 12 figs, 32 refs.