Study On The Forming Mechanism Of The Replacement Pier Under Dynamic Replacement Method

Dynamic replacement method(DRM) had been put into practical engineeringapplications as an economical and practical foundation treatment technology in the1980s. With "oceanic economy" strategy being put forward and massive coastalstructures under construction, the research of dynamic forming mechanism of fillingpiers in DRM becomes more important to engineering economy and safety. Thecurrent research of DRM mainly concentrated on dynamic consolidation, the lengthof the pier, process design, bearing mechanism of composite foundat ion, strength test,etc. Generally, we considered that dynamic compaction(DC), the forming of the pier,drainage consolidation effects, etc. act upon each other in DRM. All these above arecontributors in soil improvement. However, little research has been done in theforming of filling pier, especially in dynamic forming process.In this paper, we have studied the forming process and mechanism of filling pierby using our own DRM model test chamber and relevant measuring system. Theaccelerometer can capture the tiny variation of acceleration and the high speedcamera can record the longitudinal displacement of the pounder. Some formingmechanism can be showed in the above research work, for example, difference of thepounder in the impact test between dynamic compaction and DRM, the contributorsin several stages, etc. Finally, the numerical simulation of DRM has been conductedby FEA.The experimental results show that the curve of DRM is different from DC. Theacceleration curve can be divided into4stages. With the increasing of tamping times,the energy releasing time decreased, approximate platform shortened, the average ofacceleration reduced, the peak height becomes higher. The study indicates that thefilling design has significantly affected the energy releasing time. Meanwhile, wecan observe the motion of fillings from the dynamic photos. The force-displacementcurve of the pounder shows that the dynamic impact force becomes larger. The slopeof impact loading curve is reduced. The weak section of the impact force get shorter.