软土地区钻孔灌注桩抗震性能试验研究

选取天津市典型软土场地,针对4根纵筋配筋率不同的钢筋混凝土钻孔灌注桩展开现场足尺桩拟静力试验。探究了不同配筋率的钻孔灌注桩在低周往复水平荷载作用下的滞回特性、耗能性能、刚度退化、位移延性及承载能力的差异。试验结果表明:4根灌注桩的等效黏滞阻尼系数集中在0.10~0.23,且位移延性系数均在4.5以上,具有较好的耗能及延性性能;增大配筋率并不能明显改善钢筋混凝土钻孔灌注桩的刚度退化过程,减缓刚度退化的速率;配筋率的增加可有效提高灌注桩的塑性变形能力,增大灌注桩的极限位移,同时显著增大灌注桩的屈服荷载与极限荷载;灌注桩的耗能能力及位移延性随配筋率的增加均呈先增大后减小的变化规律,从抗震性能的角度分析,灌注桩最优配筋率的建议值为0.63%。

Experimental study on seismic behavior of bored cast-in-situ pile in soft soil area

The field pseudo-static tests on 4 full-scale reinforced concrete cast-in-situ bored piles with different reinforcement ratios are performed at a typical soft soil site of Tianjin. The seismic behavior indice, such as hysteretic behavior, energy dissipation, stiffness degradation, displacement ductility and bearing capacity of the test piles with different ratios of reinforcement under horizontal low cyclic loading, are studied. The results show that the equivalent viscous damping coefficients of four piles mainly appear between 0.10 to 0.23, and the displacement ductility coefficients of four piles are all above 4.5, indicating good energy dissipation and ductility. Increasing reinforcement ratio does not significantly improve the stiffness degradation process of the cast-in-situ bored piles and does not slow down the rate of stiffness degradation. Increasing the reinforcement ratio can effectively improve the plastic deformation capacity of the piles, and increase their ultimate displacement, and significantly increase the yield load and ultimate load of a single pile. Both the energy dissipation capacity and the displacement ductility of the piles increase firstly and then decrease with the increase of the reinforcement ratio, and based on the seismic performance of cast-in-situ piles, the recommended value of the optimal reinforcement ratio of cast-in-situ bored piles is 0.63%.