扩底抗拔桩扩大头作用机制的数值模拟研究

Uplift mechanism of enlarged base of pedestal piles by numerical analysis

在上海软土地区进行的足尺试验表明,采用小扩展角度的扩底抗拔桩能大幅提高承载力。由于没有对桩身轴力进行量测,仅凭现有的试验成果无法深入认识扩大头的作用机理。采用数值方法模拟足尺试验,通过拟合试桩中荷载-位移关系曲线,确定相关计算参数,以了解扩底抗拔桩上拔过程中扩大头抗拔阻力的组成部分及各部分在上拔过程中的变化规律,分析扩大头对抗拔承载力提高所起的作用,同时对扩大头扩径倍数、扩大头长度、扩展角度及扩大头持力层性质等主要影响因素进行了敏感性计算,可以分析这些因素的变化对承载力的影响。最后结合数值分析结果和工程实际要求对扩底抗拔桩的设计提出了建议。

The full-scale field-test on uplift behavior of pedestal piles with small extend angle enlarged base and normal straight-shafted piles has been carried out.It indicates that the uplift bearing capacity of former increases 50 percent than that of the latter.In order to know the contribution of enlarged base of pedestal pile,the composition of uplift resistance of enlarged base is analyzed by FEM.And the development of each elementary composition along with the uplift is studied.The sensitivity analysis is done for different diameters,lengths,expansion angles of enlarge base and soil characteristics in which enlarged base embedded respectively.The uplift mechanism of enlarged base is known by contrasting the result computed at different values of same parameter.Finally,some advices for design of pedestal piles with enlarged base are proposed by combination of theoretical analysis and practice.