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基于天津于家堡南地下车库工程扩底桩抗拔极限承载力试验,结合数值模拟手段对扩底桩抗拔承载特性、破坏模式和受力机制开展了分析研究。计算分析表明,扩底桩(有效桩长19 m)相比等截面桩抗拔极限承载力提高约50%,材料增加仅8.5%,扩底桩扩大头周边土体提供的抗力显著提高了抗拔承载力;荷载较小时抗拔力主要由等截面段侧摩阻力提供,扩头段抗拔力占桩顶加载的比值随加载近似呈线性增加;扩底桩等截面段沿桩土界面先发生剪切破坏,扩头段周边土体后发生受压破坏,抗拔承载力达到极限;扩头段位于同一土层时,不同桩长扩头段提供的极限抗拔力相差不大,桩长越长,扩头段抗拔力贡献率越低;扩头段抗拔力主要由自重、扩头段法向力竖向分力和侧摩阻力组成,其中法向力竖向分量提供了扩头段的主要抗拔力,占扩头段总抗拔力约70%。
Based on the test of ultimate ultimate bearing capacity of expanded-piles in underground garage at Tianjin Yujiabu South Station, numerical simulation is carried out to analyze the bearing capacity, failure mode and stress mechanism of expanded bottom piles. Computation and analysis show that the ultimate bearing capacity of expanded pile (effective pile length 19 m) is about 50% higher than that of equivalent cross-section pile, and the increase of material is only 8.5% Pull-out force; When the load is small, the pull-out force is mainly provided by the side section frictional resistance of the section, the ratio of the pull-out force to the pile top load increases linearly with the loading; Shear failure occurred after the expansion of soil around the head section of the pressure failure occurs, anti-pull bearing capacity reaches the limit; expansion head section in the same soil layer, the difference between the extension of the pile head provides the ultimate pull-up force is not significant, pile The longer the length, the lower the contribution rate of head pull-out force. The head pull-out force is mainly composed of self-weight, vertical force and lateral friction of normal head force, and the vertical component of normal force provides Expansion of the main section of the anti-pull force, head expansion accounted for about 70% of the total anti-pull-up.