考虑应力扩散时桩端土对桩体阻抗的影响

Influence of stress diffusion of soil surrounding pile tip on the pile impedance

摘要:

为研究桩端土体对桩体阻抗的影响,提出了一种模拟桩土相互作用的新模型．在该模型中,桩端应力扩散到下部土体中,土体中产生的附加应力符合圆形荷载下的Boussinesq应力解．相同附加应力形成三维等值面,将等值面包裹的土体区域看作虚土桩．虚土桩底部与基岩接触,限制竖向位移．根据虚土桩底部的边界条件,结合阻抗传递法可得到虚土桩顶部阻抗,将其作为实体桩的实际支撑参数,进而可求得整个桩体的阻抗响应．通过该模型计算得到的桩体阻抗与Novak的计算结果进行对比,发现考虑桩端应力扩散效应可以较为真实地反映桩端土体对桩体阻抗响应的影响．桩体刚度与桩端土厚度成反比,阻尼反之．对于长径比较小的桩体,桩端土体的影响更大．

Abstract:

A model for simulating the pile-soil interaction was presented in this paper to investigate the influence of soil under pile tip on the pile impedance. In this model, the diffusion of additional stress in the soil surrounding pile tip coincides with the Boussinesq’s solution under circular loading. The soil in the main zone of the stress diffusion is treated as a fictitious soil pile. The vertical displacement at the bottom of the fictitious soil pile is restrained by bedrock. The impedance on the fictitious soil pile top is obtained via the boundary conditions at the bottom of fictitious pile and impedance transfer method. This serves as the supporting condition of the actual pile, which can be further used to solve the impedance response of the whole pile system. Results of the proposed model are compared with those obtained by Novak’s method. It is found that it can yield more accurate prediction of impedance response of pile when considering the stress diffusion in base stratum. Pile damping is proportional to the thickness of base stratum, while the stiffness is on the contrary. For the pile with smaller slenderness ratio, the influence of the stratum under pile tip is more obvious on impedance.