桩土滑移的饱和土中海洋高桩竖向振动特性研究

Vertical Vibrations of Marine Pile in Layered Saturated Soil Based on Slippage Between Pile and Soil

海洋工程深水基桩下段埋置于土中,基桩上段暴露于水中和空气中,基于一维杆理论建立了饱和土中深水基桩的竖向振动简化计算模型。利用阻抗传递法,获得了深水基桩的桩顶竖向振动频域解析解和时域半解析解。计算结果表明,桩土接触相对滑移模型在接触刚度很大时与完全黏结条件下的深水基桩竖向振动响应基本一致,当接触刚度减小时,基桩动力响应增大,说明完全黏结条件过高地估计了土层的阻抗,造成桩顶响应减弱;频率相关的阻尼系数可以抑制导纳的发散效应,能够更好地模拟桩土动力相互作用。分层模型计算表明,暴露段对基桩振动产生明显影响,时域反射信号在泥面处会产生同向反射,此外,上、下土层的模量比也会对桩的振动响应产生一定的影响,这些不加以甄别会引起基桩检测误判。

In coastal and ocean engineering, the lower segment of marine pile is buried in seabed and the upper segment of pile is exposed to water and air. A simplified calculation model to analyze vertical dynamic responses of marine pile in layered saturated soil was developed based on Bernoulli theory of one-dimensional bar. By means of transfer impedances between the pile segments, an analytical solution in frequency domain of vertical vibration of piles was deduced. Then a semi-analytical solution in time domain was obtained by using convolution method. The numerical results show that the dynamic responses of pile with the imperfect contact decreased with the increasing contact stiffness between pile and soil. When the stiffness was very larger, the results agree well with the pile with perfect contact. It was deduced that the decrease of dynamic responses of pile was due to the overestimated soil impedance under the perfect contact. Frequency-dependent damping coefficient can inhibit the divergent effects of admittance and it is beneficial to simulate the dynamic interaction of soil and pile. Numerical results of dynamic responses of pile in layered saturated soil show that length of the exposed pile had a significant impact on pile vibration and a reflective signal in coordinated with incident signal at the same direction generated at the soil surface. The ratio of shear modulus of the upper and the lower soil layer also has significant effects on pile dynamic responses. All of them might be raised the misjudgment of pile testing and should be carefully distinguished with reflectometry signals of the defect of pile.