## 9 Limitations  
Several limitations were encountered in this study. The first was the lack of plugging information such as the soil column depth inside the piles, or the Incremental Filling \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**\#**} & \multirow{2}{*}{**Reference**} & \multirow{2}{*}{**Pile ID**} & **Diameter** & **Length** & \multirow{2}{*}{**L/D**} & **IFR** & \multicolumn{2}{c}{**Plugging Condition**} \\ \cline{5-8}  & & & **m (in)** & & **m (ft)** & & **(\%)** & **Actual** & **Forecasted** \\ \hline
3 & [PERSON] et al. [54] & - & 0.8 (30) & 47 (154.2) & 61.7 & 89.0 & Unplugged & N/A \\ \hline
4 & \multirow{2}{*}{[PERSON] [57]} & TP4 & 1.5 (58.8) & 73.5 (241.1) & 49.2 & 100.0 & Unplugged & Unplugged \\
5 & & TP5 & 1.5 (58.8) & 86 (282.2) & 57.6 & 100.0 & Unplugged & Unplugged \\ \hline
6 & \multirow{2}{*}{[PERSON]} & LOD1 & 1.6 (62.4) & 15.7 (51.5) & 9.9 & 65.0 & Unplugged & Unplugged \\
7 & & MOD1 & 1.6 (62.4) & 15.2 (49.9) & 9.6 & 85.0 & Unplugged & Unplugged \\
8 & & & MOD2 & 1.6 (62.4) & 16.7 (54.8) & 10.5 & 115.0 & Unplugged & Unplugged \\ \hline
9 & [PERSON] et al. [58] & - & 0.6 (24) & 30.5 (100) & 50.0 & 70.0 & Unplugged & N/A \\ \hline
10 & \multirow{2}{*}{[PERSON] et al. [59]} & P1 & 0.5 (19.2) & 22 (72.2) & 45.1 & 0.0 & Plugged & Plugged \\
11 & & P2 & 0.5 (19.2) & 22 (72.2) & 45.1 & 0.0 & Plugged & Plugged \\
12 & & P3 & 0.5 (19.2) & 22 (72.2) & 45.1 & 0.0 & Plugged & Plugged \\ \hline
13 & Olson and Shantz [29] & Bent E31R & 0.6 (24) & 13.3 (43.6) & 21.8 & 83.0 & Unplugged & N/A \\ \hline
14 & \multirow{2}{*}{[PERSON] et al. [60]} & 16 & 0.8 (32.0) & 11 (36.1) & 13.5 & 88.0 & Unplugged & N/A \\
15 & & 25 & 0.8 (32.0) & 16 (52.5) & 19.7 & 88.0 & Unplugged & N/A \\
16 & & 25 & 0.8 (32.0) & 25 (82.0) & 30.8 & 88.0 & Unplugged & N/A \\ \hline
17 & [PERSON] and Standing [61] & C1 & 0.5 (18.0) & 10 (32.8) & 21.9 & 78.0 & Unplugged & Plugged \\ \hline
18 & \multirow{2}{*}{[PERSON] et al. [62]} & P & 1.2 (48.0) & 26 (85.3) & 21.3 & 95.0 & Unplugged & Unplugged \\ \hline
19 & \multirow{4}{*}{[PERSON] et al. [63]} & K24-1 & 0.6 (24) & 33 (108.3) & 54.2 & 74.0 & Unplugged & N/A \\
20 & & K24-2 & 0.6 (24) & 39.8 (130.6) & 65.3 & 74.0 & Unplugged & N/A \\
21 & & K24-3 & 0.5 (19.2) & 39.8 (130.6) & 81.6 & 73.0 & Unplugged & Plugged \\
22 & & K34-1 & 0.6 (24) & 29.3 (96.1) & 48.1 & 82.0 & Unplugged & N/A \\ \hline
23 & \multirow{2}{*}{[PERSON] [64]} & AL 1 & 0.3 (13.2) & 15.2 (49.9) & 45.4 & 71.0 & Unplugged & Plugged \\
24 & & AL 2 & 0.3 (13.2) & 42.7 (140.1) & 127.4 & 71.0 & Unplugged & Plugged \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._Ratio (IFR). This information is necessary to positively identify the onset of plugging in pipe piles. Because nearly all the piles were not instrumented, the authors are unable to separate the effects of plugging on base and shaft resistance. In addition, the authors are unable to discern when plugging occurred. Some piles may have driven as coring, and plugged during load testing (Static Plugging), while others may have plugged during driving (Dynamic Plugging). Similarly, partial/intermittent plugging is not considered; the analysis presumes a PLR of 1 or 0, while field data generally suggest PLRs between 0.5 and 1 [3]. Finally, plugging may also influence both stiffness and load transfer, but the nature of the analysis precludes identifying these effects. Consequently, that limited the analysis to being a statistical evaluation based on the pile properties and the observed measured and computed capacities only. A second limitation was that only a few piles (8 cases) were identified as developing an internal plugging condition, leading to the decision to marginalize the internal plugging condition in the process of developing the proposed diameter criterion and in the analysis overall. The third limitation was the lack of information about the age of testing for some cases in the employed dataset. Age of testing affects pile capacity significantly, which is also associated with the actual plugging condition.