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49 TABLE 18 The performance of the drilled shafts' static analysis methods--statistical summary and resistance factors for data using mean 2 SD Resistance factors for a Capacity Design Construction No. of given reliability index Soil Type Mean COV Component Method Method Cases 2.0 2.50 3.0 Mixed 32 1.71 0.60 0.66 0.51 0.38 FHWA Casing 12 2.27 0.46 1.15 0.92 0.73 Slurry 9 1.62 0.74 0.48 0.35 0.25 Sand Mixed 32 1.22 0.67 0.41 0.31 0.23 R&W Casing 12 1.45 0.50 0.68 0.54 0.42 Slurry 9 1.32 0.62 0.49 0.37 0.28 Mixed 53 0.90 0.47 0.45 0.36 0.28 Clay FHWA Casing 13 0.84 0.50 0.39 0.31 0.24 Dry 40 0.88 0.48 0.43 0.34 0.27 Skin Friction Mixed 44 1.19 0.30 0.82 0.69 0.58 + Casing 21 1.04 0.29 0.73 0.62 0.52 End Bearing FHWA Dry 12 1.32 0.28 0.94 0.80 0.68 Sand + Slurry 10 1.29 0.27 0.94 0.80 0.69 Clay Mixed 44 1.09 0.35 0.68 0.57 0.47 Casing 21 1.01 0.42 0.55 0.45 0.36 R&W Dry 12 1.20 0.32 0.79 0.67 0.56 Slurry 10 1.16 0.25 0.88 0.76 0.65 Mixed 46 1.23 0.41 0.68 0.56 0.45 C&K Dry 29 1.29 0.40 0.73 0.60 0.49 Rock Mixed 46 1.30 0.34 0.83 0.69 0.57 IGM Dry 29 1.35 0.31 0.91 0.77 0.65 FHWA Mixed 11 1.09 0.51 0.50 0.40 0.31 Sand R&W Mixed 11 0.83 0.54 0.36 0.28 0.22 Clay F HWA Mixed 13 0.87 0.37 0.52 0.43 0.36 FHWA Mixed 14 1.25 0.29 0.87 0.75 0.63 Sand + Clay Skin R&W Mixed 14 1.24 0.41 0.69 0.56 0.46 FHWA Mix ed 39 1.08 0.41 0.60 0.49 0.40 All Soils R&W Mixed 25 1.07 0.48 0.52 0.42 0.33 C&K Mixed 16 1.18 0.46 0.60 0.48 0.38 Rock IGM Mix ed 16 1.25 0.37 0.75 0.62 0.51 Restrike data is recommended to be interpreted by 3.4.4 Static Analysis for Drilled Shafts dynamic measurements, using signal matching analy- sis (CAPWAP). Table 29 provides the recommended resistance factors to be 4. Systematically, test the number of piles according to used for the static analysis of drilled shafts. The design meth- Table 28 at the chosen time of driving (EOD or BOR). ods should be applied based on soil parameters obtained via Restrike tests following EOD tests on the same pile are a subsurface exploration program with the detailed method important for the identification of changes with time application and correlations as outlined in section 2.5, and (setup and relaxation); however, one test type should Tables 7 and 8, with further details in Appendix C. All drilled not be substituted for the other. shafts should be tested for structural integrity as recom- 5. Average the results of the tested piles. All tested piles mended in section 3.3.4.4. should be included regardless of their performance. No "good" pile result can substitute for a "bad" one, even 3.4.5 Static Load Test if a replacement is required. If the average capacity of the tested pile is greater than or equal to 85% of the Table 30 provides the recommended resistance factors for nominal ultimate capacity, then accept the set of piles static load tests under any testing procedure for both driven as "good"; otherwise reject the set as "poor." At this piles and drilled shafts. Testing of driven piles should be stage, alternative solutions are chosen, e.g., reduce the scheduled according to the recommendations provided in required nominal strength by adding piles, drive piles section 3.4.6. The site variability can be determined accord- deeper, etc. ing to the comments listed in section 3.4.3. The nominal 6. The above criteria provide a statistical approximation strength for driven piles should be determined based on for the entire pile group. From a practical point of Davisson's failure criterion or the maximum applied load if view, a separate criterion should be set as a minimum the pile does not reach failure. The same criterion should be accepted value for each pile (e.g., 1.25 to 1.5 times the used for piles tested in tension, omitting the offset displace- design load). ment of the elastic compression line. Drilled shaft capacity