静钻根植桩扩底桩端极限承载性能的试验研究

Field study on the ultimate bearing capacity of enlarged grout base of pre-bored grouted planted pile

静钻根植桩是一种绿色环保的新型植桩工法,采用下段竹节桩与桩端扩底相结合的方式,大幅提升了单桩承压或抗拔承载力,在江浙沪地区已取得了大量应用实践,但限于目前的研究现状,对于桩端扩大头的承载性能不甚明晰。基于自平衡静载试验方法,对桩端扩大头的极限抗压承载性能开展了试验研究。研究结果表明:实测桩端扩大头极限承载力相比规范计算结果提高了40%,反分析得到上海(7)层粉砂的极限端阻力折减系数为0.72~0.81,明显高于规范建议取值0.50~0.55;桩端扩大头的承载能力完全发挥所需的桩顶位移值约为0.03倍桩径,且主要由端承力控制;静钻根植桩全桩身承载能力中,扩大头部分占比达64%~67%,扩大头结构完整性对静钻根植桩工作性能起到关键作用。

Pre-bored grouted planted pile is a new type of eco-friendly pile foundation.The combination of the lower section of PHC nodular pile and the pile base expansion greatly improves the vertical bearing capacity of single pile.A lot of application practices have been achieved in Jiangsu,Zhejiang and Shanghai regions,but limited to the current research status,the bearing capacity of enlarged grout base is not clear.Based on the in-situ self-balanced loading test,the ultimate compressive bearing capacity of the enlarged grout base of the pre-bored grouted planted pile is investigated.The research results reveal that the measured ultimate bearing capacity of the enlarged grout base of the pile is 40% higher than that calculated by the specifications.The back analysis of the test results shows that the ultimate end resistance reduction coefficient of Shanghai⑦layer of silt is 0.72-0.81,which is significantly higher than the recommended value of 0.50-0.55 in the specifications.The bearing capacity of the enlarged grout base of the pile is mainly controlled by the end bearing capacity,and the required displacement value for its full bearing capacity is about 0.03 times the pile diameters.The enlarged grout base of the pile accounts for 64% to 67% of the bearing capacity of pre-bored grouted planted pile,and the structural integrity of the enlarged grout base plays a key role in the working performance of the pre-bored grouted planted pile.