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39 9 0.16 8 0.14 7 log-normal 0.12 distribution 6 mlnx = 4.53x10-4 lnx = 0.552 0.1 Number of Pile-Cases Relative Frequency 5 0.08 normal distribution 4 0.06 3 0.04 2 mx = 1.150 0.02 1 x = 0.596 0 0 0 0.5 1 1.5 2 2.5 3 KSX = Ratio of Static Load Test Results over the Pile Capacity Prediction using the Design Method Figure 21. Histogram and frequency distributions of Ksx for 56 cases of pipe and concrete pile types in sand. (COV 0.40 vs. 0.43) in spite of the large difference in the resis- The available data were analyzed and the resulting statistical tance factors. Examining the efficiency factors, one clearly parameters and associated resistance factors are presented in sees that the method that provides the highest / ratio also Table 23. The results, though based on limited data, seem to be provides the lowest "actual" factor of safety (FS ). The fac- consistent with expected behavior. Comparing the data in tors of safety presented in Table 22 for = 3.0 (the lower of Table 23 to that presented in Table 19 for driven piles under the two values in the last column) are in line with what one compression, the following can be observed: (1) large dis- would expect, ranging from 2.59 to 5.63, with an average of placement piles in clay develop similar friction under com- 3.73. The use of lower target reliability for redundant piles pression or tension, (2) friction for small displacement piles (H) ( = 2.33) provided factors of safety ranging from 2.11 to 4.00 is smaller in tension than in compression, and (3) friction under (avg. 2.94), which are judged to be reasonable as well. pullout of all piles in sand is smaller than that which develops The recommended resistance factors based on Tables 18 under compression. The recommended resistance factors for through 22 are presented in section 3.4. pullout tests are presented and discussed in section 3.4. 3.2.5 Resistance Factors 3.3 PILE TESTING for Pullout of Driven Piles 3.3.1 Overview Utilizing the University of Massachusetts Lowell static pile database, a limited number of case histories were identified for Deep foundation testing is carried out as a quality control which a static pile load test in tension (pullout) was carried out. to check or verify pile capacity and integrity. Quality control