Influence of dredging on the foundation deformation of antique stone bridge built on soft ground and its mechanistic analysis
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摘要:
在当今城市景观提质改造活动积极开展的背景之下，滨水或水域古建筑多面临着清淤的现实需求。为有效保护古建筑，需要充分考虑清淤对古建筑地基变形的影响。以某软土地基古石桥为例，建立了桥体与场地地基土层的三维模型，研究了清淤深度、清淤坡肩宽度和清淤坡比3个参数对软土地基古石桥位移和应力分布的影响规律，并进一步分析了清淤对古石桥地基变形影响的机制。研究结果表明：①清淤开挖效应主要表现为引起桥体及邻近区的土体位移、改变应力分布和导致邻近区土体出现塑性区3个方面，使得古桥自身及其邻近区土体处于更为复杂的应力场与位移场之中；②不同清淤参数对古桥及其邻近区地层位移场和应力场的影响以及影响程度存在差别，清淤深度主要影响土体的位移变化幅度，清淤坡肩宽度控制着清淤效应的波及范围，清淤坡比和清淤坡肩宽度共同影响着土体位移曲线形态的变化和塑性区的发展；③在实际清淤工作中，清淤参数的设置除了需要满足工程可行性与经济性的要求之外，还应当合理确定清淤参数、控制清淤开挖对相邻古建筑的影响程度，在确定设计清淤深度时需要综合考虑清淤坡肩宽度和清淤坡比。研究成果对古建筑的清淤工作有实际指导意义。
Abstract:Objective The great demand for urban landscape improvement and reconstruction has required increasing dredging practices for waterfront buildings, particularly antique buildings. To effectively protect such antique buildings, the influence of dredging on the ground deformation of antique buildings needs to be carefully considered in the dredging operations.
Methods To obtain a better understanding of the effect of dredging activities on antique buildings, the influence of dredging depth, dredging slope shoulder width and dredging slope ratio on the displacement and stress distribution of an antique stone bridge on soft ground via a three-dimensional model of the bridge body and its ground strata was studied in this paper. Based on the calculated results, mechanistic explanations of dredging on the ground deformation of antique stone bridges were proposed.
Results The simulated results show the following: ① Dredging effects on the antique stone bridge mainly appeared as giving rise to the displacement of the bridge and the near strata, changing the stress distribution, and forming a plastic zone in the adjacent area of strata. As a result, dredging activities render a more complex stress and displacement distribution to the bridge and the strata around the bridge. ② Different dredging parameters have different effects on the displacement fields and stress fields of the bridge and its surrounding area. The dredging depth primarily affects the displacement magnitude of the soil, and the dredging slope shoulder width is the crucial factor affecting the scope of the dredging effect, whereas the dredging slope ratio and the dredging slope shoulder width jointly manipulate the change in the soil displacement curve and the development of the plastic zone. ③ In dredging projects, the setting of dredging parameters should not only meet the requirements of engineering practicability and economy but also reasonably determine the dredging parameters and control the impact of dredging on adjacent ancient buildings and take into account the width of the dredging slope shoulder width and the dredging slope ratio when determining the designed dredging depth.
Conclusion The results in this work are of practical significance for dredging activity in antique building protection.
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Key words:
- antique stone bridge /
- dredging /
- soft ground /
- ground deformation /
- numerical simulation
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图 3 桥体两侧清淤方式示意图(单位: m)
h为清淤深度(m)；l为斜坡水平宽度(m)；D为桥墩埋置深度(m)；b为清淤坡肩宽度(m); i为清淤坡比，i=tanα=h/l；α为坡角
Figure 3. Sketch of dredging modes on both sides of the bridge
图 5 清淤前(a)和清淤后(b)桥体和场地地层竖向位移云图(h为清淤深度；i为清淤坡比；b为清淤坡肩宽度，下同)
Figure 5. Vertical displacement contour changes of bridge body and strata before (a) and after (b) dredging
图 6 清淤前(a)和清淤后(b)桥体和场地地层水平位移云图
Figure 6. Horizontal displacement contour of bridge body and strata before (a) and after (b) dredging
图 7 各记录点竖向位移增量同清淤参数的关系
Figure 7. Relationship between the vertical displacement increment of tracing points and dredging parameters
图 8 各清淤参数对桥体邻近区淤泥面处竖向位移分布的影响
Figure 8. Influence of dredging parameters on vertical displacement distribution at mud surface in vicinity of bridge
图 9 清淤前(a)和清淤后(b)桥体和场地地层剪应力云图
Figure 9. Shear stress contour of bridge body and strata before (a) and after (b) dredging
图 10 应力集中区应力增量同清淤参数的关系
Figure 10. Correlation between stress increment in stress-concentrated area and dredging parameters
图 11 清淤前(a)和清淤后(b)的地层塑性区分布
Figure 11. Distribution of the plastic zone of the before (a) and after (b) dredging
图 12 不同清淤参数与桥体邻近区地层塑性区体积比的变化关系
Figure 12. Correlation between dredging parameters and volume ratio of the plastic zone of the stratum adjacent to the bridge
表 1 古桥桥体石材及场地地层物理力学参数
Table 1. Physical and mechanical parameters of the stone of the antique bridge and the strata
地层和桥体 平均厚度
d/m干密度
ρd/(g·cm-3)剪切模量
G/MPa体积模量
K/MPa黏聚力
c/kPa抗拉强度
σt/kPa内摩擦角
φ/(°)剪胀角
ψ/(°)①淤泥层 4.0 1.0 0.52 5.00 10.0 0 9.5 0.0 ②砂淤泥过渡层 2.0 1.2 1.14 5.33 3.0 0 23.0 2.0 ③淤泥质土层 3.0 1.4 2.96 8.89 10.0 0 17.0 0.0 ④砾砂层 3.0 1.6 11.10 33.30 0.0 0 42.0 3.0 ⑤残积土层 3.0 1.5 3.70 11.10 15.0 0 23.4 0.0 桥板和桥墩 — 2.6 30 200.00 43 900.00 1 620.0 4.5 50.4 0.0 
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表 2 淤泥层其他主要物理力学性质指标
Table 2. Other physical and mechanical parameters of mucky soil
含水率ω/% 孔隙比e 饱和度Sr/% 液限ωL/% 塑限ωp/% 液性指数IL 灵敏度St 59.1 1.6 98.5 50.1 26.3 1.40 14.6
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表 3 不同工况下清淤参数设置
Table 3. Dredging parameters under different cases
清淤参数 控制条件 设置工况 清淤深度h/m — b=0 0.3 0.6 0.9 1.2 1.5 — 清淤坡比i h=1.0 b=1.0 0.58 0.84 1.00 1.19 1.73 — 清淤坡肩宽度b/m h=1.0 i=1.00 1.0 1.5 2.0 2.5 3.0 3.5
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