Horizontal bearing capacity of piles and effects of engineering treatments considering strain hardening of soil on thick silt nuclear power site
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摘要: 桩基在非基岩区核电厂相关建筑中的应用日益广泛，其水平承载力的确定与优化问题十分重要。考虑土体硬化本构模型并基于勘察资料确定合理取参方法，围绕核电厂工况构建水平承载桩基有限元模型，通过对比模型计算结果与规范经验法计算结果验证了模型的合理性，应用该模型重点分析了各类工程处理措施对桩基水平承载力的影响，研究成果表明：均匀布桩情况下，布桩形式对桩基水平承载力的影响很小，而桩径与桩基水平承载力直接相关；一般压实承台侧土可将桩基水平承载力提升10%以上，但随压实度增加后进一步提升的效果不明显；承台下进行局部土体加固的深度、宽度及加固土体刚度均会显著影响桩基水平承载力，但加固区宽度并非越宽越好；上部淤泥层预固结处理后，可将桩基水平承载力提升10%以上。另外，通过施加以上各类综合处理措施，可将桩基水平承载力提升85%以上。相关成果可为具体工况下桩基水平承载力的预测及优化提供方法路径，为工程前期阶段方案设计提供参考。Abstract: Under the current development of nuclear power plants in thick soil area, the application of piles is increasing while the determination and optimization of their horizontal bearing capacity comes to be important issues. A reasonable method was provided to determine the parameters of strain hardening model of soil based on survey data, and the finite element model was established to analyze horizontal bearing piles under nuclear power plants condition. The model was compared with the empirical method suggested by standard to verify its rationality. The impact of various engineering treatment measures on the horizontal bearing capacity of piles was analyzed in detail. The results show that as uniformly arranged, the pile arrangement form has little effect on the horizontal bearing capacity of pile group, while the pile diameter is directly related to this horizontal bearing capacity. Generally compacted soil on the side of the pile cap can increase the horizontal bearing capacity of piles by more than 10%, but the effect of further increasing compaction is not significant. The depth, width, and stiffness of the locally reinforced soil under the pile cap will significantly affect the horizontal bearing capacity of piles, but the width is not necessarily the wider the better. With the pre-consolidation treatment of the upper soft caly layer, the horizontal bearing capacity of the piles can be increased by more than 10%. Besides, by implementing the comprehensive treatment measures above, the horizontal bearing capacity of the piles can be increased by more than 85%. This study can provide a method for predicting and optimizing the horizontal bearing capacity of piles under specific conditions, and the results can provide references for the foundation design at an early stage of various engineering.
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图 1 分层土中单桩水平承载力计算模型示意图
Figure 1. Schematic diagram of horizontal bearing pile in layered soil
图 2 有限元计算与规范法计算结果对比
Figure 2. Comparison between finite element analysis and code-based calculation results
图 3 不同布桩形式及承台群桩水平承载示意图（单位：mm）
Figure 3. Different pile layouts and horizontal bearing pile groups (Unit: mm)
图 4 不同布桩形式下水平荷载–桩顶位移计算结果
Figure 4. Results of lateral load versus displacement for different pile layouts
图 5 不同桩径条件下水平荷载–桩顶位移计算结果
Figure 5. Results of lateral load versus displacement for different diameters
图 6 不同承台侧土条件下水平荷载–桩顶位移计算结果
Figure 6. Results of lateral load versus displacement under different soil conditions adjacent to the pile cap
图 7 承台下部局部水泥土加固示意图
Figure 7. Schematic of localized cement-soil reinforcement beneath the pile cap
图 8 不同水泥土加固深度影响下水平荷载–桩顶位移结果
Figure 8. Displacement under the influence of different cement depths
图 9 不同水泥土加固宽度影响下水平荷载–桩顶位移结果
Figure 9. Horizontal load – head displacement under the influence of different cement width
图 10 桩顶附近土体及结构总位移矢量图
Figure 10. Vector diagram of displacement of soil and structure near the top
图 11 不同水泥土刚度影响下水平荷载–桩顶位移计算结果
Figure 11. Displacement under the influence of different cement stiffness
图 12 淤泥层真空预压固结前后黏聚力变化试验结果
Figure 12. Experimental results of cohesion change in soft clay layer before and after vacuum preloading consolidation
图 13 淤泥层是否固结影响下水平荷载–桩顶位移计算结果
Figure 13. Horizontal load – head displacement considering whether the soft caly layer is consolidated
图 14 综合工程处理措施影响下的水平荷载–桩顶位移结果
Figure 14. Horizontal load – head displacement considering the comprehensive engineering measures
表 1 某核电项目勘察资料测定各土层参数值
Table 1. Soil parameters determined from site investigation for a nuclear power project
主要土层 土层厚
/m含水率
w/%天然密度$ {\rho }_{0} $
/(g·cm−3)土粒比重
Gs孔隙比
e塑性指数Ip 液性指数IL CU试验
总黏聚力c/kPaCU试验
总摩擦角φ/（°）压缩模量
Es1-2/kPa②淤泥层 16.4 60.8 1.62 2.76 1.744 24.31 1.35 10.08 11.07 1714 ③1粉质黏土 11.5 26.8 1.98 2.74 0.756 16.96 0.234 35.59 13.76 7047 ④粉质黏土 8.3 29.3 1.92 2.74 0.799 16.89 0.424 37.57 12.19 6906 ⑤2粉砂 4.7 1.90 2.72 2.00 28.00 11000 ⑥黏土 9.8 37.6 1.85 2.75 1.056 20.40 0.673 36.44 12.27 7590 ⑧黏土 6.81388 23.8 2.01 2.73 0.678 17.09 0.138 51.24 14.41 9766 
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表 2 有限元模拟各土层HS本构模型参数取值
Table 2. Parameters of the HS constitutive model for each soil layer
主要土层 有效黏聚力$ {c}^{\prime} $/kPa 有效内摩擦角φ'/(°) 剪胀角$ \psi $/ (°) 破坏比Rf $ E_{\rm{oed}}^{\rm{ref}} $/kPa $ E_{50}^{\rm{ref}} $/kPa $ E_{\rm{ur}}^{\rm{ref}} $/kPa $ {p}^{\rm{ref}} $/kPa $ {\nu }_{\rm{vr}} $ k0 m1 ②淤泥层 11.78 14.53 0 0.5 1542.6 1388.3 8330.0 100 0.2 0.749 0.8 ③1粉质黏土 43.73 16 0 0.95 6342.3 6976.5 27906.1 100 0.2 0.724 0.8 ④粉质黏土 44.5 14.79 0 0.95 6215.4 6836.9 27347.8 100 0.2 0.745 0.8 ⑤2粉砂 2.00 28.00 0 0.95 11000 12047 75900 100 0.2 0.531 0.6 ⑥黏土 39.94 15.55 0 0.90 6831.0 8197.2 24591.6 100 0.2 0.732 0.9 ⑧黏土 54.42 17.48 0 0.95 8789.4 10547.3 31641.8 100 0.2 0.699 0.9 回填土* 20～40 15 0 0.95 0.9Es1-2 1.1$ E_{\rm{oed}}^{\rm{ref}} $ 4$ E_{50}^{\rm{ref}} $ 100 0.2 0.741 0.9 注：*为承台侧回填土，其性质根据回填土类型及施工确定。
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表 4 桩体实际工程设计值（含淤泥层m值）
Table 4. Engineering design value of the pile (including m value of soft clay layers)
参数 工程设计值 参数 工程设计值 桩径d/m 1 混凝土弹性模量Ec/kPa 3.35×107 配筋率ρ/% 0.968 钢筋弹性模量Es/kPa 2×108 桩长l/m 55 钢筋保护层厚d0/mm 50 淤泥m值/（MN·m–4） 2.5
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表 5 综合工程处理措施对应的输入参数值
Table 5. Input parameters corresponding to engineering measures
参数 工程设计值 参数 工程设计值 桩径d/m 1 水泥土深度h/m 3/5 承台侧土Es1-2/MPa 7 水泥土加宽d′/m 3 淤泥层预固结 是 水泥土E/MPa 80
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