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219Chapter 5. The resistance factors were compared with those presented in the NCHRP Report507 and the latest AASHTO (2010) Specifications.6.4.1. PIle LOad Test (PILOT) databaseThe Iowa DOT conducted a total of 264 static pile load tests between 1966 to 1989 toimprove their pile foundation design practices. These historical test records were compiled,and an electronic PIle LOad Test (PILOT) database was developed by Roling et al. (2010) toallow for efficient analyses performed on the amassed dataset. Of these tests in PILOT, 164were performed on steel H-piles, but only 32 of them had the hammer, pile, and soilinformation required for pile resistance estimation using WEAP. Table 6.1, which showsthat steel HP 250×63 (HP 10×42) was the most commonly used pile size in Iowa, lists themeasured pile resistances obtained from static load tests (SLTs) based on the Davisson’scriterion (Davisson, 1972) and the estimated pile resistances using WEAP. For the WEAPanalysis, five different soil profile input procedures (i.e., ST, SA, Iowa Blue Book, IowaDOT and DRIVEN) described in Chapter 2 were used. It is essential to note that all pileresistances estimated using WEAP were based on hammer blow counts (i.e., number ofhammer impacts on each pile to achieve 300 mm pile penetration) recorded at the end ofdriving (EOD) condition, while the static load tests were conducted between 1 and 32 daysafter the EOD.To avoid mixing the uncertainties resulting from different soil behaviors, the PILOTdatabase was sorted into sand, clay, and mixed soil profiles, and the resistance factors wereindividually calculated for each soil type. This grouping was consistent with the AASHTO(2007) LRFD Specifications. Although AASHTO (2007) did not explain the criterion fordefining the soil profiles, a methodology for defining a site using a 70%-rule has beenaccepted by AbdelSalam et al. (2011) in the development of LRFD resistance factors forstatic analysis methods. A site is identified as sand or clay profile, if the most predominantsoil type classified in accordance with the Unified Soil Classification System (USCS) existsmore than 70% along the pile shaft embedded length. In contrast, a site with less than 70%sand or clay is identified to have a mixed soil profile. Among the 32 data records listed in