开口桩中土芯形成、影响因素及判别方法研究

开口桩打桩过程中桩端土体进入桩管内形成土芯，土芯在大直径钢管桩、新研发的大直径现浇混凝土薄壁筒桩的作用不容忽视，通过闭塞效应土芯会提高开口桩的承载力，减小桩的沉降量。比较分析了目前国际上两种土芯闭塞效应定义方法，研究认为，从土芯破坏机制出发定义土芯是否产生闭塞效应更为合理；并从土芯的形成出发，探讨了影响土芯形成及闭塞效应的各种因素，如桩径、桩端土的承载力、土芯与桩内壁的摩阻力等，此外还应考虑桩端土体侧向水平应力的影响。最后讨论了ICP方法中砂土及黏土中开口桩土芯闭塞效应的判别方式，认为该判别方式过于粗略，不能很好地反映土芯闭塞情况。

Effects on soil plugging and plugged mode in open-ended pile

During pile driving soil adjacent to pile tip comes into the tubular pile thus formed soil plug. The effect of soil plug on the bearing capacity of large-diameter steel pipe pile and new developed large-diameter cast-in-situ tubular pile can not be neglected. Through soil plugging the bearing capacity of open-ended pile will be increased and its settlement decreased. Two different definition of soil plugging were compared, and through which the definition based on the failure mechanism was verified to be more reasonable. Different effects, such as pile diameter, inner friction, vertical bearing capacity of the underlain soils and the lateral stress level, were studied. ICP discriminant of plugging mode for both clay and sand was discussed. This method was proved to be a simple one and cannot embody the real plugging in practice.