S - Kam Ng PhD Dissertation Final.pdf - Digital Repository of CCEE ...

131(R EOD ) from CAPWAP analyses. The increases in total pile resistance, shaft resistance andend bearing resistance are listed separately to illustrate the different effects on setup. Bothshaft resistance and end bearing increased with time after EOD. Referring to the lastrestrikes of all test piles, the increase in CAPWAP calculated shaft resistance ranged from51% to 71% while the end bearing resistance increased by 8% to 21%. Since the end bearingcomponent on average was about 16% of the total resistance, the impact of setup estimatedfor this component is not significant. Furthermore, the CAPWAP pile setup estimate on shaftresistance correlated well with the corresponding SLT measurements in Table 3.4 thatindicates 52% to 66% increase in shaft resistance due to setup. This observation concludesthat the setup largely affects the shaft resistance of steel H-piles.3.5.2. Assessment of pile setup trendUsing the restrike and static load test results of ISU6, the percent increase in pileresistances normalized with its initial pile resistance estimated at EOD (∆R t /R EOD ) wereplotted as a function of time (t) after EOD in Figure 3.10. Four mathematical best-fit trendsas summarized in Table 3.5 were selected to describe the relationship between the increase inpile resistance and the time given in Figure 3.10. Compared among the four trends in termsof the calculated coefficient of determination (R 2 ), the exponential equation gives the leastconfidence while the rational equation gives the best confidence in predicting the resistancegain. For long-term pile setup estimation, the constant estimation using the exponentialequation does not agree with the continuous increase in pile resistance as observed from thefield test results. Both rational and square root equations estimate relative higher increase inpile resistance than the logarithmic equation. Nevertheless, long-term restrike and load testdata are not available to evaluate them. Since restrikes and load test are normally performedwithin 14 days after EOD, the estimation of short-term pile setup is adequate for practicalapplications. Although the rational equation, which has four empirical constants, gives thebest correlation, the simpler logarithmic equation, which involves with only two empiricalconstants, provides a comparable confidence in the short-term pile setup prediction.