现浇X形桩复合地基静载荷试验研究

结合南京市桥北污水处理厂软土地基处理工程,开展了现浇X形桩单桩、单桩复合地基和多桩复合地基的静载荷试验研究,现场测得其荷载-沉降关系曲线、桩身轴力与桩侧阻力、桩土荷载分担与桩土应力比、桩侧阻力与桩端阻力的分布规律,重点论述分析了多桩复合地基竖向承载力的变化特性和规律。试验研究结果表明:X形桩单桩承载力、单桩及多桩复合地基承载力均符合设计要求;布桩间距、布桩方式及桩长是影响单桩复合地基承载力的主要因素;多桩复合地基的受力特性及变形规律与单桩复合地基基本相同;多桩复合地基桩侧阻力的整体分布规律符合传统圆形桩特点,且中性点位置在桩长的1/4～1/3处;在满足设计要求时,桩土荷载分担比例桩约为63%、土约为37%,桩土应力比约为27;桩的最大侧阻力值是桩承载力值的73.2%,具有典型的摩擦桩的特性。试验研究成果为X形桩复合地基在市政构筑物软土地基处理设计和施工应用提供了可靠的参考依据。

Static Load Field Test of X-Section Cast-in-Place Pile Composite Foundation

Based on Nanjing northbound sewage plant soft ground treatment project, a static load field test on single X-section cast-in-place pile, single and multi X-section cast-in-place pile composite foundation was carried out. The curves on load-settlement, axial force of pile shaft and side friction of pile shaft, pile-soil load sharing ratio and stress ratio, the distribution of side friction of pile shaft and pile tip resistance were measured. Multi-pile composite foundation characteristics were mainly studied. The results show that the bearing capacity of X-section pile, single and multi-pile composite foundation are all meet the design requirements; the pile distance, pile layout type and pile length are the key influence factors for both bearing capacities of single and multi-pile composite foundation. The distribution of side friction of X-section pile is similar with that of circular pile, and its neutral point is at 1/4 to 1/3 pile length. The results also show that the pile-soil load sharing ratio equals to 63%, and the pile-soil stress ratio nearly equals to 27 under the working load. Nearly 73.2% of bearing capacity of X-section cast-in-place pile is side friction of pile shaft, which means that X-section cast-in-place pile belongs to typical friction pile type. These study results of X-section pile composite foundation in soft ground treatment can provide a reliable reference for municipal structures design and construction applications.