组合桩的竖向承载力特性研究

Characteristics of the vertical bearing capacity of composite piles

组合桩是钢筋混凝土桩插入水泥土搅拌桩复合而成的新型桩。为掌握组合桩的荷载传递机理、破坏模式和竖向承载力特性,通过对3根14m长桩的载荷试验,分析了桩身轴力和桩周的侧摩阻力的分布及影响组合桩承载力因素。试验得到了组合桩的Q-S曲线、S-logt曲线、桩的极限承载力。为分析该桩竖向力的传递路线,应用有限元方法分析了混凝土桩、水泥土和桩周土的传力特点。试验和有限元分析结果表明混凝土桩的插入改变竖向荷载的传递规律,形成了从混凝土桩到水泥土再到土的传递模式,更有效地发挥了桩周的侧摩阻力;水泥土的固化效应、混凝土桩的挤土效应和混凝土桩的荷载传递是组合桩高承载力的主要来源。组合桩具有较高的单桩竖向承载力且造价低,在软土地基工程中具有广泛的应用价值。

To study the load transfer mechanism, failure pattern and vertical bearing capacity of a new-type composite pile formed by inserting a precast concrete pile into a cement mixing pile, loading tests of three full-scale composite piles were carried out. The distribution of axial force and side resistance of a composite pile and factors influencing the bearing capacity of a composite pile were analyzed from using experimental Q-S and S-logt curves, limit bearing capacity and axial strain. The load transfer mechanism of the precast concrete pile, cement soil and soil around the composite pile were also analyzed by using FEM. The experimental and analytical results indicates that load is transferred from the precast concrete pile to the cement soil and then from the cement soil to the soil around the pile, effectively utilizing the side resistance. The high bearing capacity is mainly due to the solidification effect of the cement soil, the pressing soil effect and the load transfer of the precast concrete pile. A composite pile has higher vertical bearing capacity and low cost, and thus is advantageous for soft ground.