高频振动沉桩的离散元模拟分析

应用平面颗粒离散元软件PFC2D对高频振动沉桩过程进行数值模拟分析,在细观颗粒运动层面上研究高频振动沉桩的机理,得到了桩侧摩阻力的分布变化规律,分析了贯入深度和贯入速率随时间变化规律,提出了"贯入平台期"的概念,并从能量传递和能量平衡角度分析了出现的原因,研究总结了桩周土颗粒的运动规律。结果表明:贯入度一定时,侧摩阻力随深度增加,到一定深度趋于定值;贯入度变化时,同一深度处侧摩阻力随最终贯入度增加而退化。高频振动沉桩贯入速度快,最大贯入速率能达到0.38 m/s,其中贯入平台期的出现是由于振动锤系统传递到桩的能量不足以克服贯入阻力并引起土颗粒共振。高频振动沉桩引起桩周土颗粒运动按区域分布各有特点。

Numerical analysis of piles driving by high frequency vibration using discrete element method

Numerical analysis using the PFC2D software is applied to model the process of piles driving by high frequency vibration to study its mechanism in the microscopic aspect of particle movement. Through the analysis, the distribution and change of side friction are discussed; the variation of depth and velocity during penetration with time are obtained, together with the variation of soil movements a- round the pile. The concept of penetration stagnation stage is put forward. The results show that the side friction increases with depth and would come to a relatively constant value finally with a certain pentration. In the same depth, the side friction decreases with penetration. Driven by high frequency vibration piles penetrate with high efficiency, and the top penetration rate would reach to 0.38 rn/s. The penetra- tion stagnation stage comes up when the kinetic energy of pile delivered from vibration hammer system is insufficient to overcome the penetration resistance and cause the resonance of soil particles. The soil particle movements caused by high frequency vibration have different characteristics in different regions.