Model tests on bearing behavior of pile groups in collapsible loess ground under water immersion
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摘要: 采用人工制备湿陷性黄土作为模型试验相似材料,进行2×2群桩基础浸水模型试验,对桩周土体湿陷变形规律和桩基础荷载传递特征进行分析。结果表明：土层浸水后,随浸水时间的持续,湿陷变形量-浸水时间关系曲线可划分为：初期平缓段、浸水陡降段、中期平缓段和停水后平缓段。随湿陷深度的增大,桩侧负摩阻力自上而下发展,中性点深度逐渐下移。停水稳定后,中性点深度比为0.7。在大厚度湿陷性黄土地基中,当湿陷性黄土层下限深度采用室内试验确定时,同时考虑桩顶承受工作荷载,浸水后负摩阻力的中性点深度比可参考建筑桩基技术规范取值。当土层湿陷变形处于浸水陡降期时,桩侧负摩阻力迅速发展,下拉荷载和桩端荷载增大,导致群桩基础沉降也逐渐增大,土层的湿陷与桩侧负摩阻力、群桩基础沉降的发展呈现出同步趋势。Abstract: The artificially prepared collapsible loess is used as the similar material to carry out 2×2 pile group model tests under water immersion.The change law of collapsibility deformation and the load transfer mechanism are analyzed.The results show that with the increase of soaking time, the relationship between the cumulative collapse settlement and the time mainly includes the initial gentle section, immersion steep drop section, medium gentle section and gentle section after water cut.With the increase of collapse depth, the negative frictional resistance develops from top to bottom, and the depth of neutral point moves down gradually.When the settlement achieves stability, the neutral point depth ratio is 0.7.In large-thickness collapsible loess, when the depth of collapsible loess is determined by the laboratory experiments, and considering the working load on pile top, the neutral depth ratio of negative friction resistance can be determined by the recommended value of technical specification for building pile foundation.In the steep drop period of water immersion for collapsible deformation of soil layer, the negative friction resistance acting on the pile increases rapidly, which leads to the increase of downward load and pile end load and gradual increase of the settlement of pile foundation.Collapse of soil layer presents a synchronous trend with the negative friction of pile side and the occurrence and development of pile foundation settlement.
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Keywords:
- pile foundation engineering /
- collapsible loess /
- pile group /
- negative skin friction /
- model test
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图 3 土层累计湿陷量随时间关系曲线
Figure 3. Relationship between cumulative collapse settlement and time
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图 4 桩顶沉降与浸水时间曲线
Figure 4. Relationship between settlement of pile top and time of water immersion
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图 5 浸水后基桩桩身轴力传递曲线
Figure 5. Transfer curves of axial force of pile foundation under water saturation
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图 6 浸水后基桩桩侧摩阻力分布曲线
Figure 6. Distribution curve of lateral skin friction of piles under water saturation
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