In this study, it was designed to examine the key factors as to the end-bearing capacity of drilled shaft based on the past studies, and furthermore to verify and visualize the effect on the factors systematically through the scaled model test, which has been well known as a engineering solution, and also numerical analysis using the finite differential method (Code FLAC2D) was carried out to compare with the results of scaled model experiments. It was found that rock mass strength (σc) and horizontal stress ratio (K) were the most two important factors for the end-bearing capacity of drilled shaft from the other studies in the past. Actually, the result of scaled model test and the numerical analysis showed that the end-bearing capacity of drilled shaft was greatly affected by the rock strength (σc), so it presented that there was no big difference from the existing design concepts. However, the stress condition of rock mass, which had not been considered on designs for years, was responding very sensitively to the end-bearing behavior of shaft, so it is judged that this result may suggest a new design paradigm for drilled shaft from now on.
Despite increased demand of drilled shaft and lots of studies related to optimum design, the studies on bearing capacity were focused on the skin friction up to the present (Rowe and Armitage, 1987; Rollins et al., 2005; NCHRP, 2006). It is assumed that this was caused by the fact the skin friction of drilled shaft had more effects on functioning than the end-bearing capacity based on the characteristics of initial behavior of a shaft. As this result makes it harder to carry out optimum designs by bring about the studies leaning upon nearing skin friction only, so it is estimated that more studies about endbearing capacity are required in the days to come in order to raise the understanding of entire behavioral characteristics of drilled shaft. Above all, considering the fact that skin friction and end-bearing capacity are taking place at the different displacement from each other, we cannot but regard the study of end-bearing as an absolute necessity. Accordingly, in this study, the most important factors as to the end-bearing capacity of drilled shaft were examined in order to look into the characteristic of end-bearing behavior of drilled shaft, and the scaled model test, which has been used often recently in engineering fields, was carried out to suggest the basis of judgment which is realistic and visualized.
So far, as for the end-bearing capacity of rock foundation, many studies for the end-bearing capacity from the in situ data have been achieved by some researchers. Peck et al. (1974) initially suggested end-bearing capacity of drilled shaft through the mutual relations between allowable bearing capacity and rock quality designation (RQD), and in Hong Kong, the allowable endbearing capacity (q a) was supposed based on their own rock classified table, establishing weathering, strength and Total Core Recovery (TCR) indexes as a standard (Boo, 1990).