马宏伟 刘力 汪鹏

摘 要：采用模型试验方法进行了螺距对螺纹桩竖向承载力的影响研究，结合试验结果进行了螺纹桩荷载沉降关系、承载力的构成、侧阻力分布特征、极限侧阻力以及最优螺距的分析。研究表明，螺纹桩是一种典型的端承摩擦桩，与相同外径的直孔桩相比，其具有更高的承载性能和沉降控制能力;螺纹桩的桩侧阻力随着外荷载的增加而增大，并沿桩身由上而下逐渐达到侧阻极限状态，当全长范围内均达到侧阻极限状态时，螺纹桩由于沉降迅速增大而达到承载极限状态，其极限承载能力主要由极限侧阻力决定;螺纹桩的极限侧阻力随着螺距的增大先线性增大后线性减小，当螺距内径比介于1.20～2.03之间时，侧阻增强系数可达1.9以上，最优距径比为1.36。

关键词：基础工程;螺纹桩;竖向极限承载力;侧阻增强效应

Abstract：The influence of screw pitch on the vertical bearing capacity of screw piles was studied by using a model test method. Moreover， the load-settlement curves， the bearing capacity composition， the shaft resistance characteristics， the ultimate shaft resistance and the optimal screw pitch were analyzed based on the test results. The studies show that the screw pile， as a typical end-bearing friction pile， has higher bearing capacity and settlement control ability than the ordinary pile with the same outer diameter. The shaft resistance of the screw pile increases with the increase of vertical load， and its limit state gradually presents from pile-top to pile-tip along the pile. After the pile-tip presents the ultimate shaft resistance state， the screw pile reaches the ultimate bearing state due to the rapid increase of settlement， and the ultimate shaft resistance mainly determines its ultimate vertical bearing capacity. Moreover， when the screw pitch is less than the optimal value， the ultimate shaft resistance of the screw pile increases linearly with the increase of the screw pitch size， otherwise it decreases linearly. The optimum screw pitch is 1.36 times of the inner diameter of screw pile when the ratio of screw pitch to the inner diameter is between 1.20 and 2.03 with the amplification coefficient of haft resistance exceeding 1.9.

Key words：foundation engineering; screw pile; ultimate vertical bearing capacity; amplification effect of shaft resistance

螺紋桩是一种典型的异型灌注桩基础[1]，具有工艺简单、造价低、单桩承载力高的优点，被广泛应用于实际工程之中[2]。但由于螺纹桩外形复杂，其桩-土相互作用机理仍不明确。

目前，国内外学者针对螺纹桩的承载特性问题已开展了一定的研究工作。文献[3]认为传统的螺纹桩受力分析中将螺纹结构视为环形板的简化方式是不恰当的，其在考虑螺纹的几何复杂性的基础上，采用有限单元法研究了螺纹桩在竖向压力、拉力和水平力作用下的承载特性，并开展了螺纹桩几何特征的参数化分析。为揭示螺纹桩土接触面微观破坏机制，文献[4]开展了注浆成型螺纹桩的平面离散元分析，重点研究了螺纹数量对桩-土接触面切应力-位移关系的影响。……