嵌岩特性对嵌岩桩桩顶扭转振动阻抗的影响

考虑桩身截面和桩侧土性质的变化,建立了层状土中嵌岩桩的扭转振动计算模型和控制方程; 利用Laplace变换技术和阻抗递推技术,求得任意荷载作用下嵌岩桩桩顶扭转振动复阻抗,并通过与现有解对比验证了所得解析解的合理性。基于所得解析解,在桩基础动力设计关注的低频范围内讨论了嵌岩桩几何性质、桩底沉渣、岩体性质对桩顶扭转振动复阻抗的影响。结果表明:在扭转振动条件下,嵌岩桩存在一个临界嵌岩深度,临界嵌岩深度随着桩长径比的增大和嵌岩段岩体性质的提高而降低,这说明在工程设计时,并非嵌岩深度越深对整个桩土系统承载特性越有利; 临界嵌岩深度范围内,随着嵌岩深度的增加,桩顶扭转动刚度逐渐减小,动阻尼逐渐增大,超出此范围时,嵌岩深度对桩顶扭转振动阻抗基本上没有影响; 当嵌岩深度小于临界深度时,桩底沉渣的存在会使桩顶扭转动刚度降低,动阻尼增大; 当嵌岩深度超过临界深度时,桩底沉渣对桩顶扭转振动阻抗基本上没有影响; 桩径是影响桩顶扭转振动阻抗的主要因素。

Influence of Rock-socketed Characteristics on Torsional Dynamic Impedance at Head of Rock-socketed Pile

Considering the variation of the soil and the pile cross-section, the calculating model and governing equations of a rock-socketed pile embedded in layered soil were established when there was an arbitrary torsional dynamic force acting on the pile head. The analytical solution for torsional dynamic impedance at the pile head was derived by means of Laplace transform technique and impedance function transfer method. The rationality of the present solution was also verified by comparing with existing solution. Based on the presented solution, the influence of geometrical properties of the rock-socketed pile, the sediment at pile end and the property of surrounding rock on the torsional dynamic impedance of the pile head were investigated within a lower frequency range. The result shows that there is a critical rock-socketed influence depth of rock-socketed pile under the torsional dynamic loading condition, and the critical rock-socketed influence depth decreases with the increase of the length-radius ratio of pile and the shear velocity of rock. This shows that the deeper the rock-socketed depth is not necessarily beneficial to the whole pile-soil system during the engineering design. Within the critical influence depth, the torsional dynamic stiffness decreases with the increase of rock-socketed length, but the torsional dynamic damping increases as the rock-socketed length increases. If the rock-socketed length is beyond the critical influence depth, the influence of rock-socketed on the torsional dynamic response of pile can be ignored. Within the critical influence depth, the sediment can lead to the decrease of the torsional dynamic stiffness along with the increase of the torsional dynamic impedance. If the rock-socketed length is beyond the critical influence depth, the influence of sediment on the torsional dynamic response of pile can be neglected. The pile radius is a major factor for the torsional dynamic impedance of the rock-socketed pile.