Investigation of Soil Plugging Process during Impact Driving Using a Model Pipe Pile

This study investigates the soil plugging process of an open-ended pipe pile during the impact driving through model pile tests. A semi-circular model pile with an inner diameter of 34.5 mm was driven to a depth of 500 mm along a transparent front wall of a soil tank. The authors prepared loose and dense soils with alternating colored layers of fine sands and then took photos of the entire pile driving process using a digital camera after each hammer blow. The high-definition images clearly show the effect of initial soil density on the soil plugging behavior of open-ended pipe piles. Detailed image analysis further reveals that the incremental filling ratio (IFR) repeats a trend of intermittent increase and decrease during pile driving, whereas the plug length ratio (PLR) continuously decreases as the pile penetration increases, suggesting that pipe piles may experience repeated transitions from a plugged condition to an unplugged or partially plugged condition during the impact driving process. We also computed vertical strains of the soil plugs during the pile driving process using the obtained images. Our image analyses show that the compression of the soil plug during the pile driving is more pronounced in loose sands than dense sands.