欠固结非饱和土强夯冲击动量传递关系及应用

Impact Momentum Transfer of Dynamic Compaction in Unsaturated Under-consolidated Soil and Its Application

夯锤和地层之间的相互作用是强夯地基处理效果研究的重要内容。针对欠固结非饱和土体弱胶结多孔结构的特点,忽略在强夯冲击荷载作用下弱胶结土体骨架的弹性响应,基于动量守恒原理,建立夯锤和土层系统的动量方程。通过将强夯单击加固过程表述为各微小薄层土顺次达到临界孔隙比的过程,构建强夯单击加固过程的递推格式,并将其推广于多次夯击的全过程。依据递推格式编写相应的计算程序,以北京园博园强夯加固工程为实例计算夯沉量、夯击速度、夯击时间等参数。实验表明,地基的累计夯沉量随着夯击次数逐渐增加,单击夯沉量逐渐减少,且单击夯沉量在经过多次夯击之后逐渐趋于平稳;计算结果与现场实测结果的对比表明,采用这种递推格式计算出的夯沉量数值及变化趋势和实际相符。进一步探讨了夯沉量、夯击速度随夯击时间和夯击次数的变化特性。动量递推方法为欠固结非饱和土地基强夯加固计算提供了一个新的思路,也为实际工程设计提供了参考。

The interaction between hammer and formation is a main concern in the dynamic compaction studies. According to the week cemented and porosity characteristics of the unsaturated soil under impact loading, the elasticity behavior of the unsaturated soil skeleton is not important. In this paper, the momentum equation between the hammer and the soil layers is established, and the dynamic compaction is expressed as a process of the layers reaching the ultimate porosity sequentially. The recursive equation based on the above viewpoint is also set up and extended to the whole process of the dynamic compaction. Based on the recursive equation, a computation program is developed, and furthermore, the foundation settlement, the hammer speed, the impact time and others are calculated for the example of the dynamic compaction project in Beijing Garden EXPO. It is shown that the total settlement increases with the impact number, the single settlement decreases with the number and appears to be stable after several impacts. The calculated settlement is in good agreement with the field experimental data. The tamping speed and the settlement with the tamping time are discussed in the end. The momentum recursive method provides a new way for the calculation of the dynamic compaction in the unsaturated under-consolidated soil and could be used in engineering designs.