One-dimensional analysis of soil plugs in pipe piles

Under static loading in compression, open-ended piles may fail in a plugged mode, with the soil plug moving with the pile, or in an unplugged mode, with shear failure occurring between the soil plug and the pile shaft. It may be shown that, under drained loading conditions, the former mode of failure will generally occur, because arching action within the pipe pile leads to high frictional capacity of the plug. However, under faster rates of loading relevant to the offshore environment, the increase in effective stresses within the soil plug is limited and the plug capacity is significantly lower. The Paper presents a simple one-dimensional analysis of the soil plug under partially drained conditions. The analysis has been implemented numerically, and the resulting program used to derive design charts which give the plug capacity as a function of the soil plug parameters and the rate of loading. These design charts are presented in appropriate non-dimensional form, with example calculations included for typical offshore piles in calcareous soil.