Vertical bearing characteristics of bridge pile foundation under pile-soil-fault coupling action
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摘要: 基于海南铺前大桥, 采用室内模型试验与数值仿真, 分析了断层-桩-岩土相互作用时桥梁桩基的距离效应与承载特性。研究结果表明: 在模型试验中, 对于直径为6.3 cm, 长度为60 cm的桩基, 当断层与桩基水平距离由9.45 cm增加到22.05 cm时, 承载力增幅为26.7%, 当水平距离由22.05 cm增加到31.50 cm时, 承载力增幅仅为3.8%, 断层与桩基水平距离对桩基承载力影响度降至6.5%, 可以忽略; 当桩长一定, 荷载相同时, 断层与桩基水平距离越小, 桩身轴力变化越小; 当断层与桩基水平距离由9.45 cm增加到22.05 cm时, 桩身30 cm处桩侧阻力增大了0.059 kN, 水平距离对桩侧阻力影响度降低了44.5%, 当水平距离由22.05 cm增加到31.50 cm时, 桩侧阻力增大了0.029 kN, 水平距离对桩侧阻力影响度降低了8.3%。在数值仿真中, 在桩基直径为1.5 m, 长度为30 m, 覆盖层厚度为10 m的工况下, 当断层与桩基水平距离由1.5 m增加到6.0 m时, 承载力增幅由11.0%减小到6.5%, 当水平距离由6.0 m增加到7.5 m时, 承载力增幅减小到4.9%;当断层与桩基水平距离由7.5 m减小到1.5 m时, 桩身轴力沿桩长方向减小趋势逐渐变缓, 当桩长一定, 荷载相同时, 断层与桩基水平距离越小, 桩身轴力变化越小; 当断层与桩基水平距离由1.5 m增加到6.0 m时, 桩身16 m处桩侧阻力增大了1.90 MN, 水平距离对桩侧阻力影响度降低了28.0%, 当水平距离由6.0 m增加到7.5 m时, 桩侧阻力增大了0.33 MN, 水平距离对桩侧阻力影响度降低了5.0%。模型试验与数值仿真结果均表明, 在5倍桩径范围内, 桩基竖向承载特性受断层与桩基水平距离的影响较大; 超出5倍桩径后, 水平距离的影响较小, 甚至可以忽略; 断层与桩基水平距离对承载力、桩侧阻力的影响度与桩侧阻力占比的仿真值均减小较快, 在水平距离为5倍桩径时, 较模型试验值分别降低了2.2%、6.0%、0.174, 结果较理想化, 可用作工程参考。Abstract: Based on the Hainan Puqian Bridge, the distance effect and bearing characteristics of bridge pile foundation under the fault-pile-rock interaction were analyzed by the indoor model test and numerical simulation. Research result shows that, in the model test, for a pile foundation with a diameter of 6.3 cm and a length of 60 cm, when the horizontal distance between the fault and the pile foundation increases from 9.45 cm to 22.05 cm, the bearing capacity of pile foundation increases by 26.7%. When the horizontal distance increases from 22.05 cm to 31.50 cm, the bearing capacity increases by only 3.8%, and the influence degree of the horizontal distance on the vertical bearing capacity reduces to 6.5% and may be neglected. When the length of pile foundation is constant and the load is the same, the smaller the horizontal distance, the smaller the change of axial force of pile foundation. The horizontal distance increases from 9.45 cm to 22.05 cm, the side resistance of pile foundation increases by 0.059 kN at the 30 cm of pile foundation length, and the influence degree decreases by 44.5%. When the horizontal distance increases from 22.05 cm to 31.50 cm, the side resistance increases by 0.029 kN, and the influence degree decreases by 8.3%. In the numerical simulation, under the condition that the diameter, length and overburden thickness of pile foundation are 1.5, 30, and 10 m, respectively, when the horizontal distance increases from 1.5 m to 6.0 m, the increment of the bearing capacity reduces from 11.0% to 6.5%. When the horizontal distance increases from 6.0 m to 7.5 m, the increment reduces to 4.9%. When the horizontal distance reduces from 7.5 m to 1.5 m, the axial force of pile foundation decreases gradually along the length direction of pile foundation. When the length of pile foundation is constant and the load is the same, the smaller the horizontal distance, the smaller the change of axial force of pile foundation. When the horizontal distance increases from 1.5 m to 6.0 m, the side resistance of pile foundation at the 16 m of pile foundation length increases by 1.90 MN, and the influence degree of the horizontal distance on the side resistance reduces by 28.0%. When the horizontal distance increases from 6.0 m to 7.5 m, the pile side resistance increases by 0.33 MN, and the influence degree decreases by 5.0%. The results of model test and numerical simulation show that the vertical bearing characteristics of bridge pile foundation are greatly affected by the horizontal distance between the fault and the pile foundation when the horizontal distance is less than five times the pile foundation diameter. When the horizontal distance is more than five times the pile foundation diameter, its influence is smaller or even negligible. The side resistance ratio and influence degrees of the horizontal distance on the bearing capacity and side resistance of pile foundation decrease rapider in the numerical simulation than in the indoor model test. When the horizontal distance is five times the pile foundation diameter, the numerical simulation values reduce by 0.174, 2.2%, and 6.0% compared with the indoor model test values, respectively. Therefore, the numerical simulation result is ideal and can be used as engineering reference.
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图 7 不同覆盖层厚度比例下的P-S试验曲线
Figure 7. P-S test curves under different cover thickness ratios
图 9 桩基竖向承载力影响度
Figure 9. Influence degrees of vertical bearing capacities of pile foundations
图 10 桩基竖向承载力增幅试验曲线
Figure 10. Test curves of vertical bearing capacity amplification of pile foundation
图 15 不同水平距离下的P-S仿真曲线
Figure 15. P-S simulation curves under different horizontal distances
图 16 桩基竖向承载力仿真曲线
Figure 16. Simulation curves of vertical bearing capacity of pile foundation
图 17 桩基竖向承载力增幅仿真曲线
Figure 17. Simulation curves of vertical bearing capacity amplification of pile foundation
图 20 桩基竖向承载力影响度试验曲线
Figure 20. Test curves of influence degree of vertical bearing capacity for pile foundation
图 21 桩基竖向承载力影响度仿真曲线
Figure 21. Simulation curves of influence degree of vertical bearing capacity for pile foundation
图 22 桩侧阻力影响度试验曲线
Figure 22. Test curves of influence degree of pile foundation side resistance
图 23 桩侧阻力影响度仿真曲线
Figure 23. Simulation curves of influence degree of pile foundation side resistance
表 1 模型土剪切波速
Table 1. Shear wave velocities of model soils
土体 淤泥质黏土 卵石土 微风化花岗岩 剪切波速/ (m·s-1) 138 539 917 
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表 3 断层与桩基水平距离计算工况
Table 3. Calculation conditions of horizontal distance between fault and pile foundation
分析因素 影响因素 l L/cm d1/cm h/cm 1.5d1、2.5d1、3.5d1、5.0d1 40、60、80、100 6.3 30
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表 4 数值仿真模型材料参数
Table 4. Material parameters in numerical simulation model
材料 弹性模量/MPa 泊松比 重度/ (kN·m-3) 黏聚力/kPa 摩擦角/ (°) 钢筋混凝土 41 500.00 0.20 24.0 淤泥质黏土 45.68 0.42 17.0 20 20.4 卵石土 99.80 0.28 24.0 200 30.0 微风化花岗岩 60 058.00 0.20 26.5 1 740 51.0 断层 29 000.00 0.20 25.0 0 60.0
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表 5 数值仿真计算工况
Table 5. Calculation conditions in numerical simulation
工况 分析因素 影响因素 l/m L/m d2/m h/m 1 1.5、3.0、4.5、6.0、7.5 30 1.5 10 2 60 1.8 70
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