等直径桩、扩底桩、支盘桩承载特性对比

Comparison on load-bearing characteristics among equal diameter pile,belled pile and branch pile

上部荷载作用下不同桩型桩基础的荷载传递规律不同,即不同桩型桩基础的承载特性不同,现行施工条件下可供选择的桩型较多。为研究实际工程中不同桩型桩基础的承载特性及区别,以在不同地层条件下合理地选择桩型,对同一场地的人工挖孔等直径灌注桩、人工挖孔扩底灌注桩和人工挖孔支盘灌注桩进行了现场静载荷试验,结合试验结果对比分析了上部荷载作用下3种不同桩型的桩身轴力、桩侧摩阻力、桩端阻力、极限承载力和桩身沉降的发挥性状,并研究分析其不同发挥性状产生的原因;结合双曲线拟合法分析了3种不同桩型桩基础的极限承载力。研究结果表明:扩底桩极限承载力最大,支盘桩次之,等直径桩最小;同级荷载下,扩底桩沉降最小,支盘桩次之,等直径桩最大;支盘桩的2个支盘承担荷载作用显著且表现出明显的时序性,桩身轴力和侧摩阻力在支盘处产生突变,其余桩段的桩身轴力和侧摩阻力发挥性状与等直径桩相似,上支盘分担荷载较下支盘多,支盘桩表现出多支点摩擦端承桩特性;扩底桩端扩底作用显著,其桩端阻力较支盘桩、等直径桩大,扩底上段侧摩阻力突降至0,扩底下段侧摩阻力随荷载的增加逐渐恢复,扩底桩表现出摩擦端承桩特性。该研究结果可用于类似地质桩型的选择。

The load transfer mechanisms of different types of pile foundation under upper load are different, that is, the bearing characteristics of pile foundation with different types are different. Under the current construction conditions, the choice of pile type is diverse. In order to investigate the bearing characteristics and the differences among different types of pile foundation in practical engineering, a reasonable choice of pile type was made under different stratigraphic conditions. Based on the results of field static load test on man-digged hole equal diameter pile in the same site, belled pile and branch pile, an comparative analysis of the characteristics of pile axial force, pile lateral friction, pile tip resistance, ultimate bearing capacity and pile settlement of the above three types of piles were conducted combining with experimental results. Moreover, the potential reasons for different characteristics were method, the ultimate bearing capacities of the three types analyzed. Based on hyperbolic fitting of pile foundations were analyzed. Theresults show that the bearing capacity of belled pile is the largest, the branch pile takes the second place, and the equal diameter pile is the least. Under the same load, the settlement of belled pile is the smallest, and then the branch pile follows, and the equal diameter pile is the maximum. In addition, the bearing load effect of the two branches of the branch pile is significant and shows significant time sequence. The pile axial force and lateral friction change greatly at the place of branch. The axial force and pile lateral friction resistance of the rest segments are similar to those of the diameter pile. The upper branch shares more load than the lower branch, which shows the characteristics of more friction pivot end-bearing pile. And also the belled influence on the end of belled pile is significant, tip resistance of belled pile is larger than those of the equal diameter pile and branch pile, and the lateral friction of upper belled side drops to 0 suddenly and lower belled side gradually recovers with the increasing load, which shows the characteristics of end-bearing pile. The experimental results can be used to select the type of pile in similar geological conditions.