Plugging effect of open-ended piles in sandy soil

This paper presents an experimental study of the plugging effect on the capacity of open-ended piles installed in sandy soil. Full-scale tests, including dynamic and static axial compression load tests, were carried out on three instrumented piles with different diameters (508.0, 711.2, and 914.4 mm). To measure the outer and inner shaft resistances acting on the piles, a double-walled system was utilized, with instrumented strain gauges on the outside and inside walls of the pile. The results of field tests show that the inner shaft resistance was mostly mobilized at the location between the pile tip and 18%–34% of the total plug length. It was found that the soil plugging in the lower portion has influence on the inner shaft resistance. In addition, it can be also demonstrated that the ratio of inner shaft resistance plus annulus load resistance to total resistance was decreased with increasing pile diameters. The results of these tests show that the relationship between the degree of plugging and pile diameter is clearly established. Direct observations of the soil plugs were made and used to quantify both the plug length ratio (PLR) and the incremental filling ratio (IFR). Based on this result, it was realized that the N value of the standard penetration test (SPT) is highly correlated with the IFR.