不同组合下高喷插芯组合桩抗拔承载特性试验研究

基于自主研发的大型桩基模型试验加载系统，采用砂雨法施工，对4种不同组合形式的高喷插芯组合桩（JPP桩）进行了抗拔承载性能对比试验研究。结果表明：1）JPP桩的不同组合形式对抗拔承载力有较大影响，下组合抗拔承载能力最高，其承载能力是分段组合II的1.1倍，是分段组合I的1.3倍，是上组合的1.4倍。2）极限荷载下，组合段所提供的总侧摩阻力中，下组合最高。3）在桩体上拔过程中，桩身轴力沿桩身向下依次递减；随着荷载的增加，桩身上部侧摩阻力首先达到极限值并趋于稳定，然后桩身中下部侧摩阻力逐渐发挥。4）侧摩阻力随桩土相对位移的增加而逐渐变大，在桩土相对位移较小时便达到较大值，桩身上部的侧摩阻力在达到较大值后趋于稳定，桩身中下部不同位置处的侧摩阻力在达到较大值仍有不同程度递增的趋势，总体上呈现出双曲线的分布形式。

Model test on uplift bearing behavior of JPP pile under different combinations

Model tests on the uplift bearing capacity of jet grouting soil-cement-pile strengthened piles (JPP for short) under four different combinations were carried out based on the self-developed large-scale pile foundation load test equipment system, the model piles were buried by sand pour method. The test results show that:1) different combinations have a great effect on uplift bearing capacity of JPP piles, lower combination carries the highest uplift bearing capacity, its bearing capacity is nearly 1.1 times of three-segment combination, nearly 1.3 times of two-segment combination, nearly 1.4 times of upper combination. 2) the total side resistance of lower combination is the maximum in four combinations under the ultimate uplift capacity. 3) in the process of uplifting test, axial force decreases along the pile depth under each load; the upper lateral resistance reaches firstly the ultimate value and tends to be stable, with the load increasing, the upper lateral resistance takes gradually a full play. (4) the lateral resistance increases gradually and reachs the ultimate value when the relative displacement is small for sand, upper lateral resistance tends to be stable after being ultimate value; lower lateral friction, however, has the increasing trend after reaching the ultimate. In the whole, the relationships between side friction and relative displacement show the hyperbolic model.