Factors which affect the capacity and the soil plug condition of an open-ended pile can be broadly divided into three categories; i.e., pile conditions, soil conditions and penetration methods. It has been found that the relative density and the horizontal stress have much effects on the soil plug behavior than other soil conditions, while the pile diameter is the most important factor among pile conditions. However, a few investigations have been performed to account for both soil conditions and pile conditions. In this paper, a number of calibration chamber tests have been conducted with three different sized open-ended model piles. The model pile is composed of two stainless steel pipes so as to measure the plug capacity, the tip resistance, and the outside skin friction, separately. The model pile was driven into siliceous sand, with varying soil conditions, to clarify coupled effects of pile diameter and soil conditions on the behavior, the capacity, and the load transfer mechanism of soil plug. According to the test results, as the pile diameter increases, the soil plug may not be effectively formed, especially for large relative density soil conditions. Thus, it has influence on the capacity of the pile as well as on the load transfer mechanism of soil plug.
