多元件粘弹性土模型条件下桩的纵向振动特性与时域响应

研究了桩侧土为4元件粘弹性模型(分别采用两个Voigt体串联或两个Maxwell体并联)及其简化条件下(可简化成多种三元件粘弹性模型)桩土系统的振动特性,并求得了桩顶在瞬态半正弦脉冲荷载作用下,桩的时域纵向响应的半解析解,同时结合基桩完整性检测的机械阻抗法和反射波法研究了各主要模型参数对时域及频域响应曲线的影响。试算分析表明,当采用两个Voigt体串联模型时,桩的振动特性主要受参数较小的一个控制,较大的一个则起辅助作用。而当采用双Maxwell体并联上模型时,在Maxwell体中,串联的弹簧和阻尼器通过相互耦合发挥作用,即弹簧系数的增加可表现为传统Voigt模型下阻尼作用的增强,而阻尼系数的增加则也可表现为传统Voigt模型下土刚度作用的增强,其中一个元件(弹簧或阻尼器)系数增加的极限状态(趋于无穷大)等效于另一个元件单独存在时的作用结果。研究结果表明,本文得到的理论成果相比于已有理论更加完善并能更好地反映客观实际。

Vibration of pile embedded in soil with multi-components viscous elastic model

Vibration of pile was studied and a new theory was developed, in which surrounding soil was described as multi-components visco-elastic models. In detail, one soil model is that two Voigt bodies are connected in series (called as Model A), the other is that two Maxwell bodies are connected in parallel (called as Model B). Then, a series of analytical responses in the frequency or time domain were obtained by means of Laplace transform and invert Fourier transform. Based on this, several figures were prepared to illustrate influences of soil model parameters on the responses, and some important conclusions were drawn for pile integrity test. With Model A, it is shown that the vibration characteristics of pile are influenced mainly by one Voigt body with smaller parameters, and secondarily by the other. It is also shown that fluctuation of curves of amplitude versus frequency will decrease and reflection from pile toe in velocity response of pile top in time-domain will reduce too with damping coefficient of Voigt body being increased. On the other hand, with Model B, some different regulars are found that spring or damper in a Maxwell body won't act alone, that is to say, one have to depend on the other. Out of the ordinary, the influence of increasing of damper or spring coefficient would be equivalent to that of increasing of the other to some extent from traditional angle. Either Model A or Model B could be simplified into the traditional soil model of single Voigt body. So, the new theory is more perfect than the current one.