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18 45 0.24 (1999). A comparison between the pile capacity based on Davisson's failure criterion for the slow maintained tests and 0.22 40 the static-cyclic capacity is presented in Figure 7. The obtained 0.2 relations and the associated statistical information suggest 35 that there is no significant influence on the static pile capac- 0.18 ity based on the applied static load rate. 30 0.16 The static-cyclic load test results were also compared to Number of Pile-Cases Relative Frequency log-normal distribution 0.14 the representative static pile capacity (based on the afore- 25 mx = 1.018 mentioned five methods), resulting in a mean KSC of 1.023 ^ mx = 1.013 0.12 and a standard deviation of 0.057. 20 These evaluations led to the conclusion that Davisson's lnx = 0.0829 0.1 pile failure criterion can be used to determine the reference 15 normal distribution 0.08 pile capacity for driven piles, irrespective of the pile's diam- 0.06 eter and the static load-testing procedure. 10 x = 0.1010 0.04 5 2.3.4 Failure Criterion for Statically Loaded 0.02 Drilled Shaft 0 0 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Static load tests of small- to medium-capacity drilled shafts KSD (say up to 5 MN) are similar to that of driven piles. It is com- Ratio of Representative Pile Capacity over the Pile Capacity Based on Davisson's Failure mon, however, for example in the Northeast region of the Criterion United States, to design and build high-capacity drilled shafts Figure 6. Histogram and frequency distributions of KSD (10 MN and more), often as an alternative to a large group of for 186 PD/LT2000 pile-cases in all types of soils. small-capacity driven piles. The testing for capacity of such (Paikowsky and Stenersen, 2000). shafts is a challenge that often requires alternatives to the common external reaction testing, for example, the Osterberg load-cell (Osterberg, 1992), statnamic tests (Bermingham and 2.3.3 Load Test Procedure White, 1995, Middendorp and Bielefeld, 1995), and drop for Statically Loaded Driven Piles The influence of the static load testing procedure (load- 1400 ing rate) on the designated pile capacity was examined in Equation Y = 0.924 * X Slow Maintained Static Load Test Davisson's two ways. 1200 Number of data points used = 75 R2 = 0.978351 Two detailed case histories from a research site in New- buryport, Massachusetts, were evaluated. A pipe pile and 1000 prestressed concrete heavily instrumented friction pile were Criterion (kN) tested over a lengthy period at a bridge reconstruction site. 800 Both piles were tested using three types of static load testing procedures: slow maintained (testing duration of about 45 hrs), 600 short duration (testing duration of about 6 to 8 hrs), and static cyclic (testing duration of about 15 min). Details about the piles and the testing are presented by Paikowsky and Hajduk 400 (1999, 2000) and Paikowsky et al. (1999). The interpretation Mean KSC = 0.930 Standard Deviation = 0.136 of the load-displacement relationships in both cases sug- 200 Max KSC = 1.215 gested that the test type had an insignificant influence on the Min KSC = 0.577 pile capacity (referring to a failure criterion irrespective of 0 the displacement). 0 200 400 600 800 1000 1200 1400 The effect of the test type was further investigated utilizing Static Cyclic Load Test Capacity (kN) a database containing information related to 75 piles tested 1 kN = 0.2248 kips under slow maintained and static-cyclic load testing proce- dures. In the static-cyclic procedure, the piles were loaded to Figure 7. Comparison between pile capacity based on failure using a high loading rate and then unloaded. The Davisson's criterion for slow maintained load tests and process was repeated for four cycles. The testing procedure static-cyclic load test capacity for 75 piles. (Paikowsky and its interpretation method are presented by Paikowsky et al. et al., 1999).