预制混凝土桩引扩孔复合成桩技术及其工程特性分析

Composite pile technology and bearing characteristics analysis of the pre-bored precast concrete piles

针对预制桩传统沉桩工法穿越较硬土层困难且易引发挤土效应的问题,结合合肥绕城高速路口至陇西互通立交改扩建应急工程,分别提出了引扩孔灌浆后植入预制混凝土桩技术和引扩孔浆石埋入预制混凝土桩技术,丰富了预制混凝土桩的复合成桩技术。通过现场载荷试验,验证了两工法成桩技术的适用性和可靠性,并基于数值分析对引扩孔灌浆后植入桩的承载性能进行了分析。结果表明:外围包裹层的设置可有效提升预制桩的承载性能,工程设计荷载作用下的桩顶沉降仅约1.1~3.0mm;考虑复合桩身结构特点,外围水泥砂浆包裹层对后植预制桩具有扩径和增强作用;其合理设置与选用有利于改善后植入桩的承载性能。

To solve the problem that the traditional pile driving methods of precast concrete(PC)pile are difficult to pass through the hard soil layers and tend to induce severe soil squeezing effects,a pre-bored grouted post-planted PC pile technique and a pre-bored embedded PC pile technique with grouted stone are proposed base on the emergency reconstruction project of Hefei ring expressway at Lukou-Longxi interchange.The applicability and reliability of these two techniques are verified by using the field load tests of test piles.Furthermore,the bearing characteristics of the pre-bored grouted post-planted PC pile are also analyzed based on the numerical simulation.The results show that the bearing capacity of the PC pile can be effectively improved by setting the cement mortar coating layer around the PC pile.The settlement of pile top under the design load is only about 1.1~3.0mm.The outer cement mortar coating has the effect of enlarging the diameter of the post-planted inner PC pile,so its reasonable setting and selection are beneficial to improving the bearing performance of the post-planted PC pile.