粉细砂中敞口 PHC 管桩群桩锤击施工效应

管桩的施工效应对其可打性和承载性能有着重要的影响，然而，管桩群桩施工效应的工程实录却并不多见。为此，结合某电厂粉细砂地基中敞口预应力高强混凝土（ PHC ）管桩群桩基础工程，通过土体水平位移、孔隙水压力和土塞长度的现场测试，开展了锤击施工挤土效应和土塞效应研究。考虑了群桩施工引起土体水平位移的不定向性，采用由摆式测斜仪工作原理建立的数据处理方法，分析了土体合成水平位移和运动方位角的变化规律。同时，考虑了锤击过程中孔隙水压力动态变化的实时性，采用采样时间间隔为 28 s 的自动化监测系统，对全过程孔隙水压力的变化进行了测试和分析。结果表明：在松散逐渐过渡到密实的粉细砂地基中，管桩的挤土效应和土塞的闭塞效应随入土深度的增加逐渐减弱；管桩群桩的挤土效应受到前期管桩施工引起土体的挤密作用而减弱，群桩内部的挤土效应比群桩外部的挤土效应更显著；管桩施工只引起桩头贯入位置附近土体孔压的短暂上升，而群桩的施工并不引起孔压的积聚 。

Driving response of an open-ended PHC pipe pile group in silty fine sands

Construction response of pipe piles has an important impact on their drivability and load-carrying behavior.However,very limited case histories of the construction response of pipe pile groups are available.For this purpose,field tests on soil squeezing and plugging responses to pile driving are carried out in silty fine sands in an open-ended pre-stress high strength concrete(PHC) pipe pile foundation of a power plant.In-situ soil lateral displacement,pore water pressure and soil plug length are measured.Considering the non-orientation feature of the lateral displacements,the resultant lateral displacements and movement azimuth angles are analyzed by using a data processing method derived from the working principles of pendulum-type inclinometers.Meanwhile,real-time changes in the pore water pressure during the whole process of pile driving are measured by using an automatic dynamic data acquisition system with a sampling time interval of 28 s.The results show that in silty fine sands changing gradually from loose to dense state,the soil squeezing and plugging effects decrease with the increasing penetration depth.The squeezing effect of pipe pile groups decreases due to the soil densification induced by pre-driven piles.The squeezing effect in the interior of the pile group is more significant than that in the exterior of the pile group.A short-term buildup of the pore water pressure is induced around the pile toe,and it is not accumulated during the construction of the pile group.