Large-scale model tests on performance and mechanism of inclined retaining structures of excavations
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摘要: 倾斜桩支护是较为新型的基坑无支撑支护体系,已有工程案例证明其支护性能较好,然而其支护机理尚缺乏深入研究及试验佐证。运用大型室内模型试验研究了多种倾斜桩支护结构的变形及受力特征,并分析揭示了其工作机理。试验结果表明,与悬臂支护桩相比,纯斜桩支护结构主动区土压力减小,使得变形和内力均减小；而相比悬臂直桩和纯斜桩,倾斜桩组合支护结构由于具有自撑、刚架和重力三大效应,变形及内力更小,稳定性更高。倾斜桩组合支护结构自身形成一个空间刚架,内排桩和外排桩分别发挥了类似斜撑（受压）和锚杆（受拉）的作用,受力和变形特征更接近采用内支撑的支护体系；外排桩受到的主动区摩阻力、内外排桩间土体重力均可提供抗倾覆力矩,提高了支护结构抗倾覆能力。内外排桩夹角相同时,内斜直及内外斜组合结构支护性能优于外斜直组合。Abstract: The inclined retaining structure is a relatively new braceless retaining system. The existing cases have proved that its retaining performance is better, but its working mechanism still lacks in-depth researches. In this study, the retaining performance and stability of various inclined retaining structures are investigated through large-scale model tests, and the working mechanism is analyzed and revealed. The test results show that for the purely inclined pile, the earth pressure acting on the retaining pile in the active zone of excavation decreases, making its deformation and internal force smaller than those of the cantilever pile. Compared with the cantilever piles and the purely inclined piles, due to the self-supporting effect, rigid frame effect and gravity effect, the composite inclined retaining structures have smaller deformation and internal force but higher stability, and they form a rigid frame. The inner and outer row of piles respectively play roles similar to the inclined struts (compression) and the anchors (tension), making the force and deformation characteristics of the supporting structures close to those of the retaining structures with struts. The anti-overturning moment can be provided by the friction resistance in the active zone of the outer row of piles and the gravity of soil between the inner and outer rows of piles, which improves the anti-overturning ability of the retaining structures. With the same angle between the inner and outer rows of piles, the retaining performance of composite in the ward-inclined and outward-inclined piles is better than that of the composite vertical and inward-inclined piles.
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Keywords:
- excavation /
- inclined pile /
- braceless retaining structure /
- model test
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图 1 4类典型基坑倾斜桩支护结构空间示意图
Figure 1. Diagrams of four types of inclined retaining structures
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图 2 场地土层和内斜直组合20°支护剖面图
Figure 2. Profile of soil layers and composite vertical and inward-inclined piles with inclination of 20°
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图 3 悬臂直桩和内斜直组合20°的现场监测结果
Figure 3. Monitoring results of cantilever pile and composite vertical and inward-inclined piles with inclination of 20°
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图 5 倾斜桩组合支护模型试验布置图
Figure 5. Experimental layout of composite inclined pile structures
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图 8 内斜直组合20°支护基坑开挖过程
Figure 8. Process of excavation retained by composite vertical and inward-inclined piles with inclination of 20°
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图 9 不同支护类型桩顶水平位移随基坑开挖深度变化曲线
Figure 9. Variation curve of horizontal displacement at top of retaining piles with excavation depth
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图 10 支护桩桩身位移曲线随基坑开挖深度变化
Figure 10. Variation curves of displacement of retaining piles with excavation depth
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图 11 各支护结构最大水平位移和最大弯矩对比
Figure 11. Comparison between maximum horizontal displacement and bending moment of different retaining structures
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图 13 内斜直组合支护结构土压力曲线随挖深变化
Figure 13. Curves of earth pressure of retaining piles during excavation
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图 14 挖深80 cm各支护结构支护桩土压力对比
Figure 14. Comparison of earth pressure of retaining piles at excavation of 80 cm
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图 15 各类支护结构及其桩间土的整体受力分析示意图
Figure 15. Diagram of overall stress analysis of various support structures and soil between piles
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图 16 支护桩弯矩随基坑开挖深度变化曲线
Figure 16. Variation curves of bending moment of retaining piles with depth
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图 17 支护桩轴力随基坑开挖深度变化曲线
Figure 17. Variation curves of axial force of retaining piles with excavation depth
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图 18 倾斜桩组合支护桩开挖80 cm轴力对比
Figure 18. Comparison of maximum axial force of retaining piles at excavation of 80 cm
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图 19 接近倾覆破坏时倾斜桩支护基坑滑动面开展情况
Figure 19. Sliding faces of excavation retained by inclined piles
表 1 试验用干细砂的基本参数
Table 1 Parameters of sand used in model tests
参数 Gs 平均粒径d50/mm 不均匀系数Cu 最大孔隙比emax 最小孔隙比emin 峰值摩擦角φ/(°) 数值 2.65 0.28 2.15 0.761 0.533 31 
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