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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。
Based on the design concept of settlement control, the foundation treatment of ballastless track Beijing-Shanghai high-speed railway adopts the method of raft + cushion + sparse pile to form the composite pile foundation so as to realize the optimized reinforcement scheme that effectively reduces the post-construction settlement and makes full use of the bearing capacity of the foundation. In order to explore the settlement control mechanism of the new method, the CFG pile was selected to carry out the field test of composite pile foundation. The settlement and deformation of composite pile foundations during filling, standing and unloading of high speed railway, Earth pressure, raft roof and bottom pressure. The variation of subgrade settlement, pile-soil stress ratio, load sharing ratio and raft load with filling height and consolidation time were analyzed. The results show that the raft + cushion + sparse piles combined reinforcement foundation project fully played the role of soil bearing capacity during the initial stage, resulting in differential settlement of soil between piles and piles; with the adjustment of cushion, the raft can concentrate the piles The bearing capacity of the pile body and the stress concentration of the pile head are significantly increased. The settlement of the foundation soil mainly occurs in the reinforcement zone, which reveals the bearing mechanism and deformation characteristics of the composite pile foundation under the subgrade load. The field test results can provide experimental basis for further optimizing the design parameters of CFG pile composite foundation of high speed railway.