Influence of pile-raft foundation reinforcement on subgrade of adjacent existing railway
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摘要: 在新建线桩筏地基加固过程中, 采用应力铲、水平向土应变计与测斜管对紧邻既有线路基的变形与应力进行原位监测, 分析了不同施工阶段紧邻既有线路基变形规律与受力特性。为减小测试误差, 建立了路基变形与稳定计算有限元模型, 得到了坡脚水平位移换算系数, 计算了不同开挖深度的路基最大剪应力与边坡安全系数。基于监测与计算结果, 提出了施工期跳槽浇筑、更换桩型与路基坡面喷浆挂网等既有线路基防护措施。为验证防护效果, 利用评分法与标准差法分析了轨检车数据。分析结果表明: 施工期间紧邻既有线路基累积坡脚水平位移为24.25mm, 平均每天的侧向位移小于0.59mm, 路基坡脚水平位移对施工过程反应敏感, 可作为监控既有线路基稳定状况的关键指标; 两线之间9m深度范围地基土水平应力随不同施工阶段出现挤压回缩变化, 压应力小于10kPa, 但不同施工阶段水平应力变化不明显; 浸泡条件下基坑开挖至2.2m时边坡安全系数由1.08减小为0.54, 路基失稳破坏, 因此, 施工现场必须采取既有线路基坡面防护。施工期间既有线轨检的轨道质量指数(TQI)增幅达129.58%, 既有线轨道几何线性波动较大, 但TQI小于安全限值, 即对路基防护优化后既有线路基变形得到有效控制。Abstract: During the process of pile-raft foundation reinforcement of new railway, the deformation and stress of subgrade for adjacent existing railway were measured in situ by using stress spade, horizontal strain gauge and inclinometer, and the mechanical characteristics and deformation laws of subgrade were analyzed. In order to minimize test error, a finite element model (FEM) was built to calculate the subgrade deformation and stability, the conversion factor of slope horizontal displacement was obtained, and the maximum shear stress and slope safety factors of subgrade under different excavation depths were calculated using the FEM. Based on the monitoring and calculated results, the optimized protection measures were proposed and applied during the construction process, such as pile-raft interval construction, changing pile eonstruction, and hunging mesh with steel band and grouting along the subgrade slope. The protection effect was verified with the data from track inspection car by using scoring method and standard difference method. Analysis result indicates that the cumulative slope horizontal displacement of slope foot for adjacent existing railway is 24.25 mm during construction process, and the lateral displacement per day is less than 0. 59 mm. The horizontal displacement is sensitive to the construction process and can be used as a key indicator to describe the stability of subgrade. The horizontal stress of foundation soil in the depth range from 0 to 9 m between the new railway and existing railway increases and then decreases, the compressive stress is less than 10 kPa and the stress level does not change significantly in different construction stages. The safety factor of slope decreases from 1.08 to 0.54 as the excavation depth reach 2.2 m under the soak condition, and then the state of subgrade is unstable failure, the protection measures must be adopted in the subgrade slope. The track quality index(TQI) of the existing line increases by 129.58~during the construction process, which indicates the large linear fluctuation of geometry for existing railway, but the TQI is less than its safety limit, which indicates that the deformation of subgrade is controlled effectively by using optimized protection measures.
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图 2 新建线施工对既有线路基影响
Figure 2. Influence of new line construction on existing line subgrade
图 9 基于有限元法的节点水平位移变化曲线
Figure 9. Changing curves of node horizontal displacements based on FEM
图 17 坡脚水平位移与路基最大剪应力变化曲线
Figure 17. Changing curves of slope foot's horizontal displacement and subgrade s maximum shear stress
表 1 土样物理力学性质
Table 1. Physical and mechanical properties of soil samples
表 2 轨道质量指数标准值
Table 2. Standard values of TQI
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