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Study on change of friction in pile driving in interbedded soil
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摘要: 准确确定打桩过程中的单位侧摩阻力，是提高桩基可打入性分析精度的重要途径。基于某互层土场地现场静力触探数据及高应变动测结果，分析打桩过程中单位侧摩阻力的变化规律。现场打桩全过程动测数据分析显示，与常规场地类似，在打桩过程中，同一深度的单位侧摩阻力随着贯入深度的增加而降低，总侧摩阻力表现出明显的衰减趋势；土体的互层分布对单位侧摩阻力随深度的变化趋势影响显著，表现为在砂土及粉土层中单位侧摩阻力也出现明显降低。现有的半理论半经验公式无法正确描述上述情况，对于互层土场地，建议黏土层可基于灵敏度确定折减因子，砂土和粉土宜采用与上层黏土相同的折减因子。采用该方法计算得到的单位侧摩阻与实测值基本吻合。该方法可用于互层土场地的打桩计算，提高桩基可打入性分析精度。Abstract: Accurately determining the unit friction in pile driving is very important for improving the accuracy of pile driveability analysis. Based on the in-situ cone penetration test data and high strain dynamic test results of an interbedded soil site, the change of unit friction during pile driving is studied. The results show that during the pile driving, although the total friction of pile keeps increasing with increment of penetration depth, and the total friction at the same penetration depth decreases, which is the same as that in ordinary site, the interlayered soil has a significant effect on the change of unit friction with depth. The results of analysis shows that the unit friction also decreases significantly in sand layer and silt layer in the interlayered site, which could not be described correctly with the existing semi theoretical method. In view of this, a calculation method of reduction factor in clay based on sensitivity is proposed. At the same time, it is pointed out that the same reduction factor as that of clay should be used for sandy layer and silt layer for the interlayered soil. The unit friction obtained by the proposed method is basically consistent with the measured value. The proposed method could be used in practice to improve accuracy of pile diveability analysis in an interbedded soil site.
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Key words:
- steel-pipe pile /
- pile driving /
- cone penetration test /
- unit shaft
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图 5 单位侧摩阻力计算值和实测值的比较
Figure 5. Comparison between the measured and calculated unit friction
图 7 本文方法与实测值的比较
Figure 7. Comparison between the measured and calculated unit friction with the proposed method
表 1 土层分布及桩基设计参数
Table 1. Distribution of soil layers and pile design parameters
层位 深度/m 土质描述 浮重度/（kN/m3） 不排水强度/kPa 桩土之间的外摩擦角/° 1 0~5.2 黏土和粉质黏土 7.5 2~24 2 5.2~9.2 砂质粉土与粉质黏土互层 9.4 20 3 9.2~11.6 砂质粉土 9.0 20 4 11.6~13.6 粉质黏土 8.4 40 5 13.6~20.5 粉质细砂 9.5 30 6 20.5~23.0 粉质黏土 10.0 80 7 23.0~26.0 砂质粉土 9.2 20 8 26.0~32.5 粉质黏土 9.3 90 9 32.5~37.8 砂质粉土和粉质细砂 9.4 25 10 37.8~45.3 粉质黏土 9.9 95~130 11 45.3~47.8 砂质粉土 9.2 25 12 47.8~58.5 粉质细砂 9.5 30 13 58.5~60.5 粉质黏土 9.8 160 14 60.5~64.0 黏土和粉质黏土 9.1 25 15 64.0~67.8 粉质细砂 10.3 160~200 16 67.8~69.4 粉质黏土 9.5 30 17 69.4~72.2 粉质细砂 9.7 170~190 18 72.2~76.2 粉质黏土 9.4 25 19 76.2~79.5 粉土和砂质粉土 10.0 30 20 79.5~87.9 粉质细砂 9.8 240 21 87.9~94.1 粉质黏土 9.8 20° 22 94.1~96.0 粉质细砂和砂质粉土 9.8 320 
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