中文摘要：

基于沉降控制设计理念,无砟轨道京沪高速铁路地基处理采用筏板＋垫层＋疏桩的方法,形成复合桩基以实现有效减少工后沉降和充分利用地基承载力的优化加固方案。为探索该新方法沉降控制机制,选用CFG桩开展了复合桩基现场试验研究,对复合桩基在高速铁路路基填筑、静置、预压卸载过程中的地基沉降变形、桩和桩间土土压力、筏板顶与底部压力进行了长期观测,分析了路基沉降变形、桩-土应力比和荷载分担比以及筏板的受力随填筑高度和固结时间的变化规律。研究表明：筏板＋垫层＋疏桩联合加固地基方案在初期充分发挥了桩间土承载作用,导致桩与桩间土产生差异沉降;随着垫层的调节作用,筏板可集中发挥桩体的承载能力及显著提高桩顶应力集中程度,地基土沉降主要发生在加固区范围内,从而揭示了复合桩基在路基荷载下的承载机制和变形特性。现场试验结果可为指导高速铁路CFG桩复合桩基设计参数的进一步优化提供试验依据。

英文摘要：

Based on the concept of settlement controlling design,the composite piled foundation of raft,cushion and scattered piles has been applied to the ground treatment of Beijing-Shanghai high-speed railway ballast track,in order to achieve the goals of effectively reducing the post-construction settlement and make full use of the natural foundation bearing capacity.The field test of CFG（cement fly-ash gravel） composite piled foundation has been carried out to explore settlement controlling mechanism of the foundation reinforcement technology.Through long-term observation of foundation settlement,the pressure of pile and soil,raft pressure at the top and bottom during the process of high-speed railway filling,standing and preloading and unloading;the variation laws of the embankment settlement,pile-soil stress ratio and load sharing ratio,and the variation of raft pressure with the changes of both the filling height of the embankment and the consolidation time are analyzed.The results indicate that the soil between piles shares large loading pressure in the early filling,which resulted in differential settlement between piles and soil;and then raft can significantly improve the bearing capacity of piles and stress concentration degree of pile top under the regulating role of the cushion;and the settlement of foundation soil occurs mainly in the reinforcement area.Measured results provide experimental basis for revealing the bearing mechanism and deformation characteristics of composite pile foundation,and guide the optimization of design parameters of high-speed railway CFG composite piled foundation.