不同桩体材料复合地基承载及变形性状对比试验研究

Comparative experimental research on the bearing and deformation character of composite foundations with diferent pile materials

通过室内模型试验,实测得到碎石桩、夯实水泥土桩和CFG桩复合地基桩土荷载分担比、桩土应力比和桩间土深层变形,并对三类不同桩体材料复合地基的承载及变形性状进行了对比分析.认为碎石桩复合地基和夯实水泥土桩复合地基均存在有效桩长或有效复合土层厚度;碎石桩桩长超过有效桩长,对提高复合地基承载力和压缩模量、减小变形效果不明显,除一些特别情况如为处理可液化地基外,设计桩长可适当超过有效桩长,但不宜过长;夯实水泥土桩复合地基的有效桩长与桩身强度相关性显著,应以桩身强度控制进行夯实水泥土桩桩体设计,使按桩身强度确定的单桩承载力大于或等于由桩周土及桩端土的抗力所提供的单桩承载力;CFG桩复合地基桩身强度高,桩体自身压缩性小,可全桩长发挥侧阻作用,当桩端落在好的持力层时,能很好地发挥端阻,提高承载力,减小变形,设计时应优先选择好的桩端持力层进行设计.

The pile-soil load share ratio, pile-soil stress ratio and inter-pile soil deep-seated deformation of compos-ite foundations, which include sand-gravel columns, rammed soil-cement columns and CFG piles composite ground, were measured by indoor model test. The bearing and deformation character of composite foundations were comparatively analyzed between the pile materials. An effective pile length or effective composite soil thickness exists in composite foundations with sand-gravel columns and rammed soil-cement columns. When the pile length of sand-gravel columns exceeds the effective pile length, the effect of improving the load bearing capacity, increasing the compression modulus, and decreasing the deformation is not obvious. It is inadvisable to design the pile length exceeding the effective pile length, except for treating liquefiable foundations, but the sand-gravel columns should not be too long. There is a significant correlation between the effective pile length of rammed soil-cement columns and the compressive strength of pile body; the design of pile body is dependent on the pile strength, and the load bearing capacity of a single pile derived from the pile strength should be not less than that provided by the resistance of soil around piles and pile-end soil. The CFG piles have high pile strength and small compression, and the side resistance can play along the whole pile length. The tip resistance works well when the pile tip penetrating into a good bearing layer. It is advisable to prioritize selecting a good pile-tip bearing layer for design.