Experimental and numerical studies on push-up load tests for sand plugs in a steel pipe pile

This paper focuses on the bearing capacity of soil plugs(internal shaft resistance) through fundamental research on the bearing mechanism of dry silica sand plugs. Push-up load tests onthe dry silica sand plugs inside a model pipe pile and DEM simulations were carried out to investigate the plugging behaviour. The influences of the packing state of the soil plugs(the relative density), and the height of the plugson the bearing capacity wereinvestigated. Prior to the push-up load tests, element tests onthe silica sand and DEM analyses were performed to characterise the silica sand and to determine suitable DEM analysis parameters. The experimental and DEM results clearly show that the push-up force increases significantly with the increase inthe aspect ratio of the soil plug, H/D, and with the relative density of the soil plug. The DEM analyses show a good agreement with the experimental results when the push-up force is small. Furthermore, the DEM results reveal that only the density of the soil plug in the lower portion, adjacent to the pile tip, increases gradually with theincrease inthe push-up displacement as well as the increase inH/D. Hence, it is the lower portion of the soil plug that mainly controls the capacity of the soil plug.