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weight dynamic testing. Another National Cooperative High- on their use. The associated correlations used to evaluate the
way Research Program project, NCHRP-21-08 "Innovative soil properties from SPT and CPT tests are presented in Tables
Load Testing Systems," headed by the principal author of 7a and 8, respectively. While two internal friction angle inter-
this report, examines such alternative methods. As part of pretations are listed in Table 7 and were used initially, only
this ongoing project, the static load-test results of statically the method proposed by Peck Hansen and Thornburn was
loaded drilled shafts were examined utilizing the failure cri- found to provide more realistic results, and hence utilized in
teria previously described for driven piles, and the FHWA the calibrated analyses. The methods and the correlations
criterion for drilled shafts (O'Neill and Reese, 1999). The listed in Tables 7a and 8 are based on the state of practice
FHWA criterion establishes the failure load as that associ- established via the questionnaire (see section 2.1 and Appen-
ated with a displacement of 5% of the diameter at the shaft, dix A.) Table 7b elucidates the combinations and the manner
if plunging of the shaft cannot be achieved. The results of in which the correlations were applied. The notations used
this preliminary study, presented in Table 5, suggest that in Table 7b are further noted when the analysis results are
the FHWA criterion provides a reliable and simple failure reported. The tables were, by and large, prepared as part of
interpretation. For the presented LRFD calibration study, the the study of static pile capacity at the University of Florida,
FHWA failure criterion for drilled shaft (i.e., load at a dis- which is presented in Appendix C.
placement of 0.05 B) was, therefore, adopted.
2.5 DRIVEN PILES--DYNAMIC ANALYSIS
2.4 DRIVEN PILES--STATIC ANALYSIS METHODS
METHODS
2.5.1 Overview
Table 6 presents a summary of the methods used for static
capacity evaluation of driven piles detailing the equations for Prior to detailed analyses leading to the determination of
side and tip resistances, required parameters, and constraints resistance factors, two components must be established: (1) the
TABLE 5 Evaluation of failure criteria for statically loaded drilled shafts
Statistics for the Ratio between Drilled Shaft Capacity of Different Interpretation Methods
and the Representative Capacity
Davisson DeBeer Shape of Curve FHWA
# mx x # mx x # mx x # mx x
47 0.862 0.17 39 0.908 0.11 36 0.956 0.09 40 0.999 0.13
Notes: # = no. of cases; mx = mean; x=standard deviation; loads 0.85 to 20 MN; diameter 0.3 to 1.5m;
length 5.3 to 58.5m
TABLE 6 Summary of static capacity methods for driven piles
Method Side resistance Tip resistance Parameters Constraints
required
Su; +Bearing layer must be stiff
-Tomlinson
Db (bearing cohesive
(Tomlinson, 1980/1995) qs = Su embedment) + Number of soil layers 2
-API (Reese et al.,
Su
1998) qp = 9 Su
in cohesive (AASHTO,
qs = ' OCR
1996/2000)
(US Army Corps of
qs = ('+2Su) Su Only for cohesive soils
Engineers, 1992)
in cohesionless
' Dr
(Bowles, 1996)
Nordlund and Thurman sin( + ) qp =
q s = K C F'
(Hannigan et al., 1995) cos t N'q '
Meyerhof SPT (Meyer- qp = + For cohesionless soils
qs = k N N
hof, 1976/1981) 0.4D/BN' + SPT data
Schmertmann SPT (Lai
qs = function(N) qp = fn(N) N SPTdata
and Graham, 1995)
Schmertmann CPT
(McVay and Townsend, qs = function(fs) qp = fn(qc) qc, fs CPT data
1989)
