强夯置换软土中碎石墩形成过程的试验研究

Experimental study of forming process of replacement pier in soft soil using dynamic replacement method

强夯置换工程要求保证夯沉量、置换墩长度等设计指标,通常通过试夯确定必要夯击次数。研究置换墩形成机制,确定夯锤能量释放时间、填料运动规律、锤底动压力等因素,对优化强夯置换工艺有重要作用。目前有关置换墩形成机制的研究较少,往往套用强夯工程的基本参数或机制来解决。针对这一问题设计了一种模型试验方法,研究强夯冲击下填料、软土与夯锤之间的相互作用过程。试验研究表明:每次夯击中夯锤的运动加速度曲线可以分为4个阶段,分别代表了夯锤作用下土体-填料的不同运动过程;通过分析夯锤的动态力-位移曲线,阐述各阶段随夯击和填料次数变化而发生的变化及原因;随填料次数的增加,在相同夯击能下,每次夯击中夯锤的能量释放时间减小,峰值动态力增加,这反映了随着夯击次数增加,软土基础中碎石墩逐渐形成的过程。

In a dynamic replacement（DR） process, the length and the subsidence of the replacement pier need to meet the design specifications. The times of tampings and the fillings to fulfill a DR process is generally determined by field test. Understanding the forming mechanism of the replacement pier, and quantifying the factors such as energy releasing time, motion characteristics of fillers, stress of pounder bottom, etc, play critical roles for optimizing the DR process. In this paper, a model test method to study the interactions of the fillers and soil under the multiple impacts of the pounder is established. Experimental rusults show that each acceleration-time curve in DR can be divided into four stages, representing different phases of the soil-fillers motions under each pounding. Through analyzing the force-displacement（F-s） curves of the pounder in this process, the characteristics of each F-s curve are distinguished and the intrinsic mechanism is discussed. It was shown that with the increasing of filling times, the energy releasing time during each pounding decreases and the maximal force increases, signifying the gradual forming of the replacement pier in the soft soil foundation.