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Robust geotechnical design and analysis of horizontal bearing capacity of laterally loaded pile
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摘要: 针对岩土参数不确定性对单桩水平承载力的影响, 以及水平荷载波动引起的单桩设计方案水平承载力考虑不足问题, 提出基于可靠度理论的单桩水平承载力鲁棒性设计思路。先将岩土参数和水平荷载作为不确定因素, 利用平均值及标准差考虑参数变异性; 其次将桩身几何尺寸、配筋率及混凝土强度作为设计参数, 同时考虑桩顶边界条件, 按照抵抗桩顶水平位移的挠度失效模式与抵抗桩身弯矩的强度失效模式作为目标函数进行单桩水平承载力设计。鲁棒性设计避免了传统设计忽略岩土参数不确定的不合理问题, 将鲁棒性作为安全性评价标准, 结合经济性对水平承载桩基进行多目标优化设计。通过与传统设计对比分析, 证明了鲁棒性设计的合理性与重要性。分析表明:桩径和配筋率的增加可显著提高单桩水平承载力, 而桩身混凝土强度对抵抗桩顶位移的作用并不明显且经济性较差。
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关键词:
- 水平承载桩 /
- Pasternak双参数地基 /
- 不确定性 /
- 鲁棒性 /
- 经济性
Abstract: The horizontal bearing capacity of the laterally loaded pile is influenced by the uncertainty of soil parameters and the fluctuation of the horizontal loads will increase the risks of failure of the pile. In order to solve these problems, a robust geotechnical design (RGD) based on the reliability is presented in this study as a new geotechnical design concept. First, the mean and standard deviation of the soil parameters are investigated to clarify the uncertainty of the soil parameters in the RGD method. And then the size of the pile, the reinforcement ratio and the concrete strength are taken into consideration as the design parameters, and the boundary conditions of the pile top are also analyzed. The horizontal deflection failure modes (DFM) and the resistance of bending moment strength failure modes (SFM) of the pile top are used as a target function in the design of the horizontal bearing capacity of a single pile. As a safe evaluation standard, the design robustness is used to evaluate the feasibility of the design scheme for the horizontal bearing capacity of the single pile with the RGD method. By use of the RGD approach, the cost efficiency and robustness are the optimun target to achieve the multi-objective engineering optimization. The design scheme satisfies the bearing capacity requirements. Meanwhile, the cost efficiency and robustness of the design are guaranteed. Comparing with the traditional design methodology, the rationality and importance of the RGD are proved in this study. Analysis results show that the increase of the pile diameter and the reinforcement ratio can significantly improve the horizontal bearing capacity of the single pile, but the effect of the concrete strength of the pile shaft on the resistance to the pile head displacement is not remarkable and its economic benefit is poor. -
图 4 鲁棒性设计方法计算的水平桩基失效概率
Figure 4. Probability of failure of laterally loaded pile obtained by RGD
图 6 混凝土强度对水平桩鲁棒性设计的影响
Figure 6. Influence of concrete on laterally loaded pile obtained by RGD
图 7 桩顶自由条件多目标优化
Figure 7. Multi-objective optimization of free-head laterally loaded pile
图 8 桩顶嵌固条件多目标优化
Figure 8. Multi-objective optimization of fixed-head laterally loaded pile
表 1 干扰因素
Table 1. Parameters of noise factors
参数 分布类型 平均值 变异系数范围 N 正态分布 20 0.1~0.3 F 极值Ⅰ型分布 200 kN 0.2~0.5 
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表 2 一次可靠度与蒙特卡洛法计算的设计失效概率
Table 2. Failure probabilities of deterministic design by FORM and Monte Carlo simulation
计算方法 挠度失效 强度失效 自由 嵌固 自由 嵌固 蒙特卡洛法 0.465 1.9E-3 0.988 0.028 一次可靠度法 0.369 1.09E-4 0.999 1.765E-4 误差(%) 20.6 94.3 1.1 99.4
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