大面积填土场地中摩擦型桩负摩阻力分布特性研究

中国大面积场地形成工程日益增多，在缓解土地供求矛盾的同时也带来了诸多工程问题，如场地大面积沉降会造成桩基负摩阻力增加，影响桩基安全性，但针对大面积填土场地中桩基负摩阻力研究成果较少。结合某现场试验，建立了单桩有限元分析模型，与实测数据对比验证模型的合理性。基于验证后的数值分析模型，研究了大面积填土场地工程中填土天然重度及厚度、桩顶和地表荷载及场地形成时间对摩擦型桩下拉荷载和中性点的影响。结果表明，填土厚度和桩顶荷载的变化显著影响中性点的位置；填土的天然重度和厚度越大，下拉荷载越大；场地固结时间越长，下拉荷载越小；减小桩顶荷载和增加地表堆载会增大下拉荷载。敏感度分析表明，相比荷载因素，场地形成因素对下拉荷载及桩顶沉降影响更为显著。最后，结合国内外规范讨论了考虑大面积填土场地中摩擦型桩负摩阻力计算方法的适用性。研究结果对大面积填土场地摩擦型桩设计具有参考价值。

Investigation on distribution of negative friction of frictional piles in large filling sites

In recent years, the number of large-area filling sites projects have been greatly increased in China. This can alleviate contradictions between supply and demand of construction lands. However, it also gives rise to many engineering problems. For example, subsidence of large area site increases negative skin friction(NSF) on pile shaft, which affects the pile safety. However, there have been limit studies on NSF of frictional piles occur in large area filling sites. Based on a field test, a single pile finite element analysis model is established, and the rationality of the model is verified by comparing with the measured data. Based on the verified numerical model, influences of weight and thickness of fill, load on pile head, surcharge loading and field consolidation time on skin friction of a single frictional pile are studied. The results show that fill thickness and load on pile head play major influences on neutral point position. An increased negative frictional force is associated with an increase in thickness and weight of fill, and a reduction in fill consolidation time. It is also linked to a reduction of load on pile head and increase in surcharge. Sensitivity analysis show that factors related to fill formation play a more significant role in NSF of pile shaft than the loading factors. The applicability of the common design methods used at home and overseas, calculating the NSF of frictional pile in large filling sites is discussed. The results can provide guidance for engineering application of frictional pile in large filling sites.