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动刚度是桩基动测分析中一个重要指标,研究动刚度的影响因素有着现实的工程意义。为了分析完整桩和缺陷桩单桩动刚度的变化规律和影响因素,推导并求解了竖向简谐荷载作用下考虑两个变截面桩的导纳响应解析解。利用测试数据验证了该模型能有效计算导纳共振频率值和动刚度值。同时,对513根相同型式桥桩进行机械阻抗法测试,并对其动刚度进行统计分析。研究表明:(1)桩端支撑刚度和桩长对动刚度影响较大,端承桩动刚度随桩长增加而降低,纯摩擦桩情况与之相反。摩擦桩在桩长较长时其动刚度可能大于端承桩。(2)桩身缺陷体积改变量与动刚度变化成正相关。(3)动刚度对桩身缩颈缺陷敏感度较高,在一定程度上可以用于判断桩身完整性和承载能力。
Dynamic stiffness is an important index in the dynamic analysis of pile foundation. It is of practical engineering significance to study the influencing factors of dynamic stiffness. In order to analyze the variation regularity and influencing factors of dynamic rigidity of single pile with intact and defective piles, the analytic solution of admittance of two piles with varying cross section subjected to vertical simple harmonic loads is deduced and solved. The test data verify that the model can effectively calculate the admittance resonance frequency and the dynamic stiffness value. At the same time, 513 identical type piles were tested by mechanical impedance method, and their dynamic stiffness was statistically analyzed. The results show that: (1) The stiffness and pile length of pile tip have a great influence on the dynamic stiffness. The dynamic stiffness of the pile ends decreases with the increase of pile length, but the situation of pure friction pile is the opposite. The dynamic stiffness of the friction pile may be greater than that of the end bearing pile when the pile length is longer. (2) The volume change of pile defects is positively correlated with the change of dynamic stiffness. (3) The dynamic stiffness is more sensitive to the necking defects of the pile, and to a certain extent, it can be used to judge the integrity and carrying capacity of the pile.