Development of Rock Embedded Drilled Shaft Resistance Factors in Korea based on Field Tests
Round 1
Reviewer 1 Report
This paper presents the calibration of resistance factors in Korea based on load test data. The study incorporates load tests on drilled shafts in the rock bed. It can be a good reference for future studies on rock because not many area-specific studies have been performed for calibration of resistance factors for drilled shafts in rock. However, a few clarifications and corrections will improve the quality of the paper. The format of the paper (i.e., fonts, spacings) needs improvement. Detailed comments are provided as follows -
1. Font size in the figures is not consistent. For example, axis title in Figure 6 has a larger font size than the axis title in Figure 5.
2. Line 160 – the font is inconsistent
3. Numbering format of Equation 1 is not consistent with Equation 2. Also, the spacing before and after Equation 1 is not similar to the other equations.
4. Table 11 has an inconsistent font of the column titles. The 1st part has bold font as column titles but the 2nd and 3rd parts have regular font.
5. In the introduction part, several previous studies on the calibration of resistance factors were mentioned. But there was no discussion on the results of those previous studies. A comparison of the results of calibration studies in Korea with the resistance factor values suggested by AASHTO would be helpful.
6. The base resistance of TP2 was omitted from the statistical analysis due to the very high bias resistance value. How does this procedure of omitting data affect the bias distribution?
7. In Tables 6, 7 & 8 showing the calculated bias factors, a few of the 13 load test cases are missing. No explanation was provided on the reason behind omitting these load test cases.
8. The study was performed based on only 13 load test cases. An explanation of the effect of this low number of load tests on the calibration will be helpful for future reference.
9. As the database consists of drilled shafts majorly in rock, I’d suggest incorporating that information in the title of the paper.
Author Response
Response to Reviewer 1 Comments
Point 1: Font size in the figures is not consistent. For example, axis title in Figure 6 has a larger font size than the axis title in Figure 5
Response 1:
As your review, Figure 6 was revised. The revised Figure 6 was shown in line 204.
Point 2: Line 160 – the font is inconsistent
Response 2:
The font in line 160 was checked and unified.
Point 3: Numbering format of Equation 1 is not consistent with Equation 2. Also, the spacing before and after Equation 1 is not similar to the other equations.
Response 3:
The numbering format and spacing of Equation 1 was modified. The modified equation was descried on line 137.
Point 4: Table 11 has an inconsistent font of the column titles. The 1st part has bold font as column titles but the 2nd and 3rd parts have regular font.
Response 4:
As your review, the fonts of the column titles were inconsistent in manuscript including Table 11. So we made the rules that column titles of each tables should be bold, and all column titles were modified to bold.
Point 5: In the introduction part, several previous studies on the calibration of resistance factors were mentioned. But there was no discussion on the results of those previous studies. A comparison of the results of calibration studies in Korea with the resistance factor values suggested by AASHTO would be helpful.
Response 5:
According to reviewer opinion, resistance factors for each references were added in manuscripts.
The added explanations for AASHTO resistance factors were included in manuscript as follows.
“Resistance factors for drilled shaft in rock from AASHTO were suggested as 0.50~0.55 for shaft resistance factors and 0.50 for base resistances.”
This additional explanation was described in line 44.
Also, resistance calibration results in Korea were reflected in manuscript as follows.
“Considering these discrepancies, a great deal of research into resistance factors has been conducted in Korea. In 2008, the Korea Institute of Construction Technology [9] suggested total resistance factors for driven steel pipe piles (0.29~0.38 for target reliability index of 2.33) and drilled shafts (0.20~0.70 for target reliability index of 3.0). Jung [10] proposed total, shaft, and base resistance factors for drilled shafts using a numerical analysis. From Jung’s research, resistance factors for target reliability index of 3.0 were determined as 0.55~0.80 for total resistance, 0.20 for shaft resistance, and 0.20~0.70 for base resistance. Kim et al. [11] suggested the base and shaft resistance factors for axially loaded driven piles in sands based on the Imperial College pile (ICP) design method. The calculated resistance factors (target reliability index of 3.0) were 0.61~0.86 for base resistance and 0.55~0.96 for shaft resistance. Park [12-13] updated the total resistance factors for driven steel pipe piles based on Bayesian theory to incorporate the results of proof tests. The updated resistance factors were determined as 0.19~0.71 for target reliability index of 3.0. Recently, there were some researches to suggest the resistance factors for deep foundations using load test data in domestic region [14-15] and researches for suggestion of resistance factors and comparison according to design methods for shallow foundations [16-17]. “
This modified paragraph was described from line 55 to line 69.
Point 6: The base resistance of TP2 was omitted from the statistical analysis due to the very high bias resistance value. How does this procedure of omitting data affect the bias distribution?
Response 6:
In case of Carter & Kulhawy, statistics based on all data were calculated as follows; mean as 1.55, Standard deviation as 1.11, and COV as 0.72. However, boundary of bias factors were calculated as 3.77(mean plus times of standard deviation), so outlying data (bias factor of TP 2 as 3.80 in Table 7) was omitted for statistical analysis. Consequently, statistics were calculated based on 9 data (excluding TP 2), and results were summarized in Table 9.
This additional explanation was described in line 289.
Point 7: In Tables 6, 7 & 8 showing the calculated bias factors, a few of the 13 load test cases are missing. No explanation was provided on the reason behind omitting these load test cases.
Response 7:
In this study, 13 load test cases were collected and used. These load tests were planned to install the strain gauge by depth and perform the load transfer analysis. From load transfer analysis, shaft and base resistances were separately determined and summarized as measured resistances in Table 6, 7 & 8. However, due to some reasons like site condition, pile construction quality and proficiency of engineer, load transfer analysis was not able to perform in some cases especially Site 3(TP 9 ~ TP 13). The strain gauge condition of test piles in Site 3(TP 9 ~ TP 13) were not good to measure the strain and perform the load transfer analysis, it was impossible to determine the shaft resistances. So, only base resistances for TP 9 ~ TP13 were used for this study.
This additional explanation was described in line 270.
Point 8: The study was performed based on only 13 load test cases. An explanation of the effect of this low number of load tests on the calibration will be helpful for future reference.
According to reviewer opinion, additional explanation was added as follows.
“Also, suggested resistance factors were based on only 13 load test cases considering regional characteristics in Korea. But, if additional load test data will be collected, LRFD methods can be updated and calibrated the resistance factors based on reliability analysis. So, results in this study are expected to be helpful for future reference.”
This additional explanation was described in line 346 and line 380.
Point 9: As the database consists of drilled shafts majorly in rock, I’d suggest incorporating that information in the title of the paper.
Response 9:
According to reviewer opinion, the title of the paper will be change as follows.
Development of “Rock Embedded” Drilled Shaft Resistance Factors in Korea based on Field Tests
Thanks for your reviews.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Very interesting article.
Only minor comments, if authors choose to do it:
Figs 1 to 3 are not sharp enough; but still readable in the PDF version. Authors may enhance them.
No. of decimal places in Table 2 may be reduced to one decimal place.
It may be better using MPa instead of kPa.
Other than that, the paper is excellent.
Author Response
Response to Reviewer 2 Comments
Point 1: Figs 1 to 3 are not sharp enough; but still readable in the PDF version. Authors may enhance them.
Response 1:
As your review, Figure 1, 2 and 3 was revised. The revised Figures were shown from line 102 to line 107.
Point 2: No. of decimal places in Table 2 may be reduced to one decimal place.
Response 2:
According to reviewer opinion (Point 2 and Point 3), Table 2 was modified. Unit of applied load was change from kN to MN and decimal place was reduced. Table 2 was modified as follows.
Table 2. Test program
Shaft no. | Loading type | Load (MN) |
TP 1 | Bi-directional loading test | 105.5 |
TP 2 | 49.1 | |
TP 3 | 44.1 | |
TP 4 | 36.8 | |
TP 5 | 206.0 | |
TP 6 | 166.8 | |
TP 7 | 117.7 | |
TP 8 | 88.3 | |
TP 9 | Top-down static loading test | 19.1 |
TP 10 | 17.7 | |
TP 11 | 17.7 | |
TP 12 | 17.7 | |
TP 13 | 17.7 |
This modified table was summarized in line 118.
Point 3: It may be better using MPa instead of kPa.
Response 3:
According to reviewer opinion, Table 6 was modified as follows. Unit of resistance was changed from kPa to MPa. This modified table was summarized in line 280.
Table 6. Calculated bias factors for shaft resistance
Depth(m) | Measured shaft resistance (MPa) | Carter & Kulhawy (1988) | Horvath & Kenney (1979) | FHWA (1999) | Rowe & Armitage (1987) | |||||
Predicted resistance (MPa) | Bias factor | Predicted resistance (MPa) | Bias factor | Predicted resistance (MPa) | Bias factor | Predicted resistance (MPa) | Bias factor | |||
TP1 | 35.0-36.0 | 1.22 | 0.36 | 1.53 | 0.38 | 1.44 | 0.36 | 1.51 | 0.83 | 0.66 |
36.0-37.0 | 2.45 | 0.80 | 3.18 | 0.85 | 2.99 | 0.81 | 3.15 | 1.84 | 1.38 | |
37.0-38.7 | 1.90 | 0.77 | 2.09 | 0.82 | 1.96 | 0.78 | 2.07 | 1.77 | 0.91 | |
TP2 | 28.8-32.9 | 0.81 | 0.89 | 0.9 | 0.95 | 0.85 | 0.90 | 0.89 | 2.06 | 0.39 |
32.9-33.9 | 0.89 | 0.77 | 1.16 | 0.82 | 1.09 | 0.78 | 1.14 | 1.77 | 0.5 | |
33.9-35.3 | 2.06 | 1.03 | 2 | 1.10 | 1.88 | 1.04 | 1.98 | 2.37 | 0.87 | |
TP3 | 26.9-28.0 | 0.68 | 0.57 | 1.19 | 0.61 | 1.12 | 0.58 | 1.18 | 1.32 | 0.52 |
28.0-29.0 | 0.37 | 0.65 | 0.57 | 0.69 | 0.54 | 0.66 | 0.56 | 1.50 | 0.25 | |
29.0-30.0 | 1.40 | 0.82 | 1.7 | 0.88 | 1.6 | 0.83 | 1.69 | 1.90 | 0.74 | |
30.0-31.0 | 1.79 | 0.81 | 2.21 | 0.86 | 2.08 | 0.82 | 2.19 | 1.86 | 0.96 | |
31.0-33.1 | 2.69 | 0.67 | 4.02 | 0.71 | 3.78 | 0.68 | 3.98 | 1.54 | 1.74 | |
TP4 | 24.0-30.5 | 0.24 | 0.27 | 0.87 | 0.29 | 0.82 | 0.28 | 0.86 | 0.63 | 0.38 |
TP5 | 44.0-46.5 | 0.32 | 2.18 | 0.15 | 2.32 | 0.14 | 2.20 | 0.15 | 5.01 | 0.06 |
46.5-48.5 | 2.85 | 2.58 | 1.1 | 2.75 | 1.04 | 2.61 | 1.09 | 5.95 | 0.48 | |
48.5-50.5 | 2.00 | 2.85 | 0.7 | 3.03 | 0.66 | 2.88 | 0.69 | 6.56 | 0.3 | |
50.5-52.5 | 1.44 | 2.67 | 0.54 | 2.84 | 0.51 | 2.69 | 0.54 | 6.14 | 0.23 | |
52.5-54.5 | 1.52 | 1.26 | 1.2 | 1.34 | 1.13 | 1.27 | 1.19 | 2.90 | 0.52 | |
TP7 | 45.5-50.21 | 3.35 | 1.36 | 2.46 | 1.45 | 2.31 | 1.37 | 2.44 | 3.13 | 1.07 |
TP8 | 46.26-48.26 | 1.22 | 0.28 | 4.36 | 0.30 | 4.1 | 0.28 | 4.32 | 0.64 | 1.89 |
48.26-49.76 | 1.17 | 0.38 | 3.04 | 0.41 | 2.85 | 0.39 | 3.01 | 0.88 | 1.32 | |
49.76-51.35 | 1.60 | 0.55 | 2.9 | 0.59 | 2.73 | 0.56 | 2.87 | 1.27 | 1.26 | |
Also, bearing capacity equations in Table 4 were still expressed in kPa unit. It is because that bearing capacity equations in Korea specifications were expressed in kPa unit. So, to avoid the confusion for readers, we decided to maintain the unit in Table 4 as kPa.
Thanks for your reviews.
Author Response File: Author Response.docx
