Effect of soil plugging on axial capacity of open-ended pipe piles in sands

A degree of soil plugging during pile driving affects the ultimate capacity of open-ended pipe piles. A few researchers have attempted to quantify the effect of soil plugging on pile capacity by introducing PLR (plug length ratio), ratio of length of soil plug to pile penetration depth. However, the majority of these attempts were based on model pile tests conducted in the laboratory that may not be directly applicable to field conditions due to scale effects. In this paper, we measured plug lengths at final penetration depths for 1,355 open-ended driven pipe piles with pile diameters ranging between 406 mm and 914 mm. These piles were driven mainly in dense to very dense sandy soils. The pile penetration depths ranged between about 10 m and 30 m. Our analyses indicated that the PLR values increased with the increase in pile diameter in the given soil conditions. We performed PDA (pile driving analyzer) tests on 99 piles and estimated skin friction and end bearing values of the 99 piles from CAPWAP (CAse Pile Wave Analysis Program) analyses. The results from our analysis indicated that unit skin friction and unit end bearing values increased with decreasing PLR. We suggested new design equations for estimation of skin friction factor β and end bearing factor Nq for piles driven in dense to very dense sands.