为研究高填深挖地基厚填土明洞结构承载高、地基处理复杂、沉降变形不均匀等技术问题，以广湛高铁机场隧道为背景，分析不同明洞结构型式与布桩方案受力特征，提出合理的结构设计方案；系统对比规范中桩基承载力计算方法，研究桩周土性、堆载压力等因素作用下桩周负摩阻的演化规律，明确桩基承载力计算原则；梳理规范中复合地基沉降计算方法，进行适用性评价，提出填挖过渡段的沉降控制措施。研究结果表明： 1）填方段明洞宜采用斜墙平底大墙脚+粗桩疏布的结构型式，挖方段明洞宜采用直墙仰拱结构型式； 2）桩基承载力计算采用容许应力法更为保守，桩周负摩阻力具有“消散效应”,需控制单次回填厚度并对桩周不良地层进行改良； 3）挖方段地基沉降宜按照刚性桩采用桩体压缩法进行计算，可考虑采用素混凝土桩来有效衔接钻孔灌注桩与CFG桩，并通过桩顶垫层厚度的调整实现地基沉降的均匀过渡。
There exist many technical
issues of thickly-filled open-cut tunnel with highly-filled and deeply-excavated foundation, such as high load-bearing
capacity of structure, complex foundation treatment, and uneven settlement
deformation. A case study is conducted on the Guangzhou-Zhanjiang high-speed railway, and the
structural load bearing characteristics of open-cut
tunnel and pile arrangement plans are analyzed, proposing a rational structural
design plan. The load bearing capacity calculation methods of the pile in
various specifications are compared, and the evolution pattern of negative
frictional resistance around the pile under the action of soil properties and
stacking pressure is examined, clarifying the calculation principles load
bearing capacity of pile. Additionally, the calculation methods of the
foundation settlement in composite strata are summarized, and feasibility
assessment is conducted, proposing settlement control measures in transition
section between filling and excavation. The research results reveal the
following: (1) Inclined wall, flat bottom, and large arch foot structure with
large-diameter and large span piles should be adopted
for the open-cut tunnel in the filled section, whereas
straight wall and inverted arch structure should be adopted for that in the
excavated section. (2) The allowable stress method is more conservative than
the probabilistic limit state method in calculating pile foundation load. The
negative friction resistance around the pile is dissipated, thus a single-time backfill thickness should be controlled and the unfavorable
strata around piles should be conditioned. (3) The foundation settlement of the
open-cut tunnel in the filled section can be calculated
as the rigid piles and using the pile compression method. The plain concrete
piles can be used to effectively connect drilling piles and cement fly-ash gravel piles, and the thickness of the pile top cushion can be
adjusted to achieve a uniform transition of foundation settlement.
