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33 CHAPTER 3 INTERPRETATION, APPRAISAL, AND APPLICATIONS 3.1 ANALYSIS RESULTS tion 2.5.3). The PD/LT 2000 database was first separated into AND RESISTANCE FACTORS design and construction categories. The dynamic methods used in construction were subdivided between methods that 3.1.1 Driven Piles--Static Analysis use dynamic measurements and those that do not. These, in turn, were subcategorized according to the controlling param- Table 16 presents a summary of the results obtained from eters. Figure 27 presents the analyzed subsets, the number of the analyses used for static capacity evaluation of driven piles, case histories in each set, and the mean and standard devia- compared with the nominal resistance based on Davisson's tion for each. failure criterion. The information is grouped by soil and pile WEAP is utilized in the design stage. The analysis (not type and design method. The table includes statistical param- included in this research) needs to be carried out for driving eters and resistance factors for a range of reliability index stress evaluation, leading to a load factor. The use of the values, and a ratio of DL to LL of 2.0. method for the evaluation of pile capacity was examined The data leading to Table 16 were statistically analyzed to remove outliers (i.e., extreme cases; Section 3.5 provides a through the comparison of WEAP results for default input val- discussion of this process); and the table includes only those ues and the blow count at the EOD with static load test results. cases within 2 standard deviations of the mean. As can be The data presented were provided by GRL Inc. (Hannigan seen, subcategorization based on pile or soil type may result et al., 1996). in subsets too small for reasonable statistical analysis. On the For the construction category, the dynamic analyses meth- other hand, many of the subsets have similar statistics and ods without dynamic measurements are the ENR, Gates, resistance factors and hence can be combined. It is important and FHWA version of Gates. The methods with dynamic to note that many common design methods for all piles in all measurements are CAPWAP and the Energy Approach. The soils overpredict the actual (i.e., measured) pile-capacity. dynamic methods are broken down into subsets based on time This explains the traditional need for high factors of safety of driving, driving resistance, and area ratios. Judgment and for static design (e.g., see Table 1). statistical guidelines were used for the inclusion or exclusion A more complete picture of the performance of a method is of cases. For example, extreme CAPWAP underpredictions obtained by plotting the histogram of observed to predicted (beyond 2 standard deviations) were observed at EOD at one capacities and overlaying the best-fitting normal and lognor- site. All the case histories on that site included easy driving mal PDFs. Figures 17 through 26 present such plots for the and large area ratios; if included in the general population of selected cases of static analyses of driven piles. The figures the data, the EOD statistics would have become 1.861 1.483 are arranged in order from the most inclusive logical case, as (mean 1 S.D.). This site is included only in the subcategory the data permit, to subsets of the same category. For example, of blow count < 16 BP10cm and AR < 350. Figure 17 presents the performance of the -API method for all pile types (52 cases of H, concrete and pipe piles) in clay. Figures 18 and 19 present the performance of the method for 3.1.2.2 The Critical Categories subsets of concrete (36 cases) and H piles (16 cases), respectively. Additional graphical presentations of the data The outcomes of the statistical analyses presented in Figure are included in Appendix C. 27 allow the identification of critical categories that require calibration and development into resistance factors. For exam- 3.1.2 Driven Piles--Dynamic Analysis ple, the critical CAPWAP cases include (1) all data, (2) EOD, (3) BOR, and (4) the worst combination of soil motion effect 3.1.2.1 The Analyzed Cases (Blow count < 16 BP10cm and AR < 350). Table 17 presents a summary of the major categories of the dynamic methods Time of driving, driving resistance, and area ratio proved identified from Figure 27 as those that require calibration for to be controlling parameters for the dynamic methods (sec- a resistance factor.

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34 TABLE 16 The performance of the driven piles' static analysis methods--statistical summary and resistance factors for data using mean 2 SD Resistance Factors Soil Pile (1) Details of Method(2) Stand. for a Given N Design Method Mean COV Type Type Application Dev. Reliability Index 2.00 2.50 3.00 4 -Method 11.5 B; T&P(2) 0.61 0.37 0.61 0.23 0.18 0.13 16 -Method 11.5B; T&P(2) 2B; T&P(5) 0.74 0.29 0.39 0.43 0.35 0.29 H-Piles 17 -Tomlinson 2B; T&P(2) 0.82 0.33 0.40 0.46 0.38 0.31 16 -API 2B; T&P(5) 0.90 0.37 0.41 0.50 0.41 0.33 8 SPT-97 mob 1.04 0.43 0.41 0.57 0.47 0.38 18 -Method 2B; Hara (5h) 0.76 0.22 0.29 0.53 0.45 0.38 Concrete 17 -API 2B; Hara (5h) 0.81 0.21 0.26 0.60 0.52 0.44 Clay Piles 8 -Method 2B; Hara (5h) 0.81 0.41 0.51 0.37 0.30 0.23 18 -Tomlinson 2B; Hara (5h) 0.87 0.42 0.48 0.42 0.34 0.26 18 -Tomlinson 2B; T&P (1) 0.64 0.32 0.50 0.30 0.24 0.19 19 -API 2B; T&P (1) 0.79 0.43 0.54 0.34 0.27 0.20 Pipe Piles 12 -Method 2B; T&P (1) 0.45 0.27 0.60 0.17 0.13 0.10 19 -Method 2B; T&P (1) 0.67 0.37 0.55 0.28 0.22 0.17 12 SP T-97 mob 2B; T&P (1) 0.39 0.24 0.62 0.15 0.11 0.08 19 Nordlund 36; 11.5B,P(6) 0.94 0.38 0.40 0.53 0.43 0.35 18 Meyerhof 0.81 0.31 0.38 0.47 0.39 0.32 H-Piles 19 -Method 36; 2B; P(5) 0.78 0.40 0.51 0.36 0.28 0.22 18 SPT-97 mob 1.35 0.58 0.43 0.72 0.59 0.47 36 Nordlund 36: 11.5B; P(6) 1.02 0.49 0.48 0.50 0.40 0.31 Concrete 35 -Method 36; 2B; P(5) 1.10 0.48 0.44 0.58 0.47 0.38 Sand Piles 36 Meyerhof 0.61 0.37 0.61 0.23 0.18 0.13 36 SPT-97 mob 1.21 0.57 0.47 0.60 0.48 0.38 19 Nordlund 36; 2B P(5) 1.48 0.77 0.52 0.67 0.52 0.41 Pipe 20 -Method 36; 2B P(5) 1.18 0.73 0.62 0.44 0.33 0.25 Piles 20 Meyerhof 0.94 0.55 0.59 0.37 0.29 0.22 19 SPT-97 mob 1.58 0.82 0.52 0.71 0.56 0.44 20 -Tomlinson/Nordlund/Thurman 36; 2B; P(5) 0.59 0.23 0.39 0.34 0.28 0.23 34 -API/Nordlund/Thurman 36; 2B; P(5) 0.79 0.35 0.44 0.41 0.33 0.27 H-Piles 32 -Method/Thurman 36; 2B; P(5) 0.48 0.23 0.48 0.23 0.19 0.15 40 SP T-97 1.23 0.55 0.45 0.64 0.51 0.41 33 -Tomlinson/Nordlund/Thurman 36; 2B; P; Hara(5h) 0.96 0.47 0.49 0.46 0.36 0.29 80 -API/Nordland/Thurman 36; 11.5B; Sch; T&P(8) 0.87 0.42 0.48 0.42 0.34 0.26 Concrete Mixed Piles 80 -Method/Thurman 36; 11.5B; Sch; T&P(8) 0.81 0.31 0.38 0.47 0.39 0.32 Soils 71 SPT-97 mob 1.81 0.91 0.50 0.84 0.67 0.52 30 FHWA CPT 0.84 0.26 0.31 0.57 0.48 0.40 13 -Tomlinson/Nordlund/Thurman 36; 2B; P(5) 0.74 0.44 0.59 0.29 0.22 0.17 Pipe 32 -API/Nordland/Thurman 36; 2B; P(5) 0.80 0.36 0.45 0.41 0.33 0.26 Piles 29 -Method/Thurman 36; 2B; P(5) 0.54 0.26 0.48 0.26 0.21 0.16 33 SPT-97 mob 0.76 0.29 0.38 0.45 0.37 0.30 (1) See Table 6 for details; (2) Numbers in parentheses refer to notations used for detailing soil parameters combinations (see Table 7b and Appendix C for more details), See Tables 7a and 8 for soil properties' correlations to SPT and CPT respectively, 36 = limiting friction angle, B = pile diameter 2B, 11.5B contributing zone to tip resistance.