# Development of Rock Embedded Drilled Shaft Resistance Factors in Korea based on Field Tests
## 2 Evaluation of Resistance for the Drilled Shaft  
### Collected Load Test Data  
It is critical that accurate resistance values be determined. In the procedure for reliability-based resistance factor calibration, the measured resistance value can significantly influence the results of the reliability analysis and thus the subsequent the resistance factor calibration. Therefore, load test data obtained by strain gauges located in test drilled shafts were collected to provide accurate measurements of the shaft and base resistance. Based on these accurate shaft, base, and total resistance values obtained from the load transfer analysis, sufficiently accurate resistance factors can be determined.  
In this study, a total of 13 sets of in-situ drilled shaft load test results were collected from three sites: shaft tests TP1-TP4 and TP5-TP8 were conducted on two different bridge construction sites and shaft tests TP9-TP13 were conducted on a building construction site (see Figures 1-3 for site characteristics). Sites 1 and 2, corresponding to TP1-TP4 and TP5-TP8, respectively, contained large-diameter shafts,  
Over the last few decades, the bi-directional load test has been widely used to test drilled shafts due to its advantages compared to conventional top-down pile load tests. Among the load tests considered in this study, bi-directional load tests were used in Sites 1 and 2 in order to apply sufficient loading for the large-diameter drilled shafts. However, the shaft diameters in Site 3 were smaller, so bi-directional tests were not necessary to provide sufficient loading. Therefore, conventional pile (top-down) static loading tests were applied. The test programs are summarized in Table 2.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Shift No.** & \begin{tabular}{c} **Shift Length** \\ **(m)** \\ \end{tabular} & \begin{tabular}{c} **Embedded Depth** \\ **(m)** \\ \end{tabular} & \begin{tabular}{c} **Shaft Diameter** \\ **(m)** \\ \end{tabular} & \begin{tabular}{c} **Construction** \\ **Site** \\ \end{tabular} & **Rock Type** & \begin{tabular}{c} **Weathering** \\ **Degree\({}^{*}\)** \\ \end{tabular} & \begin{tabular}{c} **Unconfined** \\ **Strength** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **RQD** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{c} **TCR** \\ **(\%)** \\ \end{tabular} \\ \hline TP 1 & 18.96 & 38.96 & 2.35 & & & & \\ \hline TP 2 & 20.61 & 36.21 & 1.85 & & & & \\ \hline TP 3 & 9.11 & 33.41 & 1.35 & Site 1 (Bridge) & \begin{tabular}{c} Gneiss \& \\ schist \\ \end{tabular} & \begin{tabular}{c} Weathered \\ and soft rock \\ \end{tabular} & 10.2–25.4 & 22–78 & 53–100 \\ \hline TP 4 & 35.38 & 36.38 & 1.85 & & & & \\ \hline TP 5 & 40.14 & 55.42 & 3 & & & \\ \hline TP 6 & 44.10 & 56.60 & 2.4 & & & \\ \hline TP 7 & 45.10 & 51.20 & 2.4 & Site 2 (Bridge) & \begin{tabular}{c} Biotite \\ granite \& \\ pegantic \\ \end{tabular} & \begin{tabular}{c} Weathered \\ and soft rock \\ \end{tabular} & 44–47 & 0–42 & 90–100 \\ \hline TP 8 & 40.01 & 52.26 & 2.4 & & & \\ \hline TP 9 & 14.0 & 14.0 & 1.5 & & & \\ \hline TP 10 & 13.5 & 13.5 & 1.0 & & & \\ \hline TP 11 & 13.5 & 13.5 & 1.0 & Site 3 (Building) & \
\begin{tabular}{c} Gneiss \\ (Building) \\ \end{tabular} &
\begin{tabular}{c} Weathered \\ and soft rock \\ \end{tabular} & 38 & 0 & 100 \\ \hline TP 12 & 13.5 & 13.5 & 1.0 & & & \\ \hline TP 13 & 13.5 & 13.5 & 1.0 & & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Test shaft profile and site investigation results.  
Figure 3: Site investigation results (Site 3).