钻孔灌注桩桩底沉渣对桩承载性状影响

Influence of bottom sediment on the bearing capacity of pedrilled cast-in-place pile

为了对沉渣影响桩的承载特性进行定量研究。根据现场检测试验资料,建立有桩底沉渣的钻孔灌注桩单桩桩土相互作用轴对称弹塑性有限元模型,从桩底沉渣厚度、物理特性以及长径比变化3个方面分析沉渣对桩承载性状影响进行研究。计算结果表明,沉渣的存在降低了桩极限承载力,沉渣厚度越大,沉渣对Q-S曲线影响也越大;当沉渣厚度大于300 mm时,桩端阻力降低幅度明显;桩底沉渣一定程度上减少了桩身变形;在对桩底沉渣物理参数进行研究的结果表明,沉渣弹性模量和摩擦系数对桩极限承载力影响明显;长径比越大,桩底沉渣对桩承载力及沉降影响越小。根据上部荷载作用下沉渣变形特性分析,当沉渣性质较弱时,桩的破坏模式更多地表现为一种刺入剪切破坏,与现场测试结果一致。

Quantitative research was conducted to analyze the influence of bottom sediment. The axisymmetric elastic-plastic finite element model of soil-pile interaction of single pile was established based onthe-spot test data. Influence analysis of bottom sediment on the bearing capacity of predrilled cast-in-place pile was made from the thickness, the physical properties and the change of length diameter ratio of bottom sediment. The finite element calculation results show that the existence of bottom sediment decreases the ultimate bearing capacity of pile, and that the thicker the bottom sediment is, the more influence on QS curve it will make. When the thickness of bottom sediment is over 300 mm, it will decrease the pile tip resistance greatly. The bottom sediment decreases, to a certain extent, the deformation of pile body. The result of physical parameters of bottom sediment shows that the elastic modulus and the friction coefficient of bottom sediment have great impact on the ultimate bearing capacity of pile,and that the larger the length diameter ratio is, the less influence the bottom sediment will make on the bearing capacity of pile. According to the analysis of the deformation properties of the bottom sediment under top loading, when the bottom sediment is weak, the failure mode of the pile is more likely to manifest itself as punching shear failure features.