为研究冲击荷载作用下桩周土体的动力响应特征及土动力参数合理取值,应用SPAX-2000动静真三轴仪进行佛山淤泥质土动三轴试验,分析了冲击荷载作用下周围压力、振动次数和频率对土的动剪应力、液化应力比、阻尼比、动模量的响应规律。结果表明:(1)动剪应力随着围压或振动频率的增大而提高,随着振动次数的增加而减小,当周围压力从100 kPa上升至400 kPa时,动剪应力下降幅度为67.1%~45.2%;(2)与1 Hz比较,振动频率为10 Hz的动剪应力相应高出44.3%~72.6%,动剪应力受周围压力、振动频率和振动次数的影响较大;(3)各变形阶段的动模量(初始模量、加载平均模量、加载最大模量和卸载模量)均受周围压力和振动频率影响显著,动模量随着振动频率或围压增大而增大;(4)阻尼比随围压增长近似线性递减,周围围压由100 kPa增大到400 kPa时,阻尼比则由0.285减小至0.153,阻尼比受振动频率影响不明显。研究成果可为管桩设计、高应变测试分析提供动力参数并为类似工程提供参考。

In order to study the dynamic response characteristics of the soil around the pile under impact load and the reasonable values of soil dynamic parameters, dynamic triaxial tests were conducted on the muddy soil in Foshan using the SPAX-2000 dynamic -static true triaxial system. The response law of surrounding pressure, vibration frequency and frequency to dynamic Shear stress, liquefaction stress ratio, damping ratio and dynamic modulus of soil under impact load. The results show that: (1) The variation law of soil dynamic shear stress shows that the dynamic shear stress increases with the increase of confining pressure or vibration frequency, and decreases with the increase of vibration frequency. The surrounding pressure varies from 100 kPa to 400 kPa, the dynamic shear stress decreases from 67.1% to 45.2%. The dynamic shear stress at a frequency of 10 Hz is higher than that of 1 Hz by 44.3% to 72.6%. The surrounding pressure, vibration frequency and number of vibrations have a great influence on the dynamic strength of soil. (2) The variation law of dynamic modulus of soil parameters shows that the dynamic modulus of each deformation stage (initial modulus, average loading modulus, maximum loading modulus, and unloading modulus) is significantly affected by surrounding pressure and vibration frequency. The dynamic modulus increases with the increase of vibration frequency or confining pressure. (3) The variation law of soil damping ratio shows that the damping ratio decreases approximately linearly with the increase of confining pressure. When the confining pressure varies from 100 kPa to 400 kPa, the damping ratio is reduced from 0.285 to 0.153, and the vibration frequency has no obvious effect on the damping ratio. The research results can provide reference for the design of pipe piles, dynamic parameters for high-strain test analysis or similar projects.