现浇X形桩复合地基桩土应力比及负摩阻力现场试验

结合南京市桥北污水处理厂软基处理工程,开展了现浇X形桩(简称X形桩)单桩及单桩复合地基竖向承载力特性现场试验,测得了荷载-沉降曲线、桩土应力比、桩身轴力以及桩侧负摩阻力等分布规律,分析了不同桩间距与荷载等级下复合地基中桩土协调相互作用和荷载分担比;并进行了同等条件下等混凝土用量圆形桩竖向承载力特性试验和分析。结果表明:复合地基中X形桩桩侧负摩阻力主要发生在0.27倍桩长以上;同等条件下,桩侧负摩阻力最大值约为其正摩阻力最大值的60%;X形桩复合地基桩土荷载分担比较普通圆形桩复合地基桩土荷载分担比更合理,承载力也更高。

Field Test of Pile-soil Stress Ratio and Negative Skin Friction of Composite X-section Cast-in-place Pile Foundation

Based on soft ground improvement engineering of Nanjing Bridge North Sewage Treatment Plant,field tests of the vertical bearing capacity of X-section cast-in-place concrete pile(referred to as XCC pile),composite foundation and pile foundation were carried out.The distribution rules of load-settlement curves,pile-soil stress ratio,axial force of pile shaft and negative skin friction of pile side were measured.Then,the pile-soil interaction and load sharing ratio under different pile spaces and loading levels in composite foundation were analyzed.In order to make comparative analysis,the field tests on vertical bearing capacity characteristics of circular piles with the same concrete amount were carried out.Results show that the negative skin friction of XCC pile in composite foundation mainly occurs over 0.27 times of pile length.The maximum value of negative skin friction is about 60% of that of positive skin friction.The pile-soil load sharing ratios of XCC pile composite foundation are better than those of circular pile composite foundation,and bearing capacity of XCC pile composite foundation is better than that of circular pile composite foundation under the same condition.