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

69blows/ft) or less is required to fully mobilize the soil resistance. Also, re-striketesting is recommended with a few hammer blows to minimize the loss of the effectof soil setup or soil relaxation.4. A driving hammer shall have the sufficient impact force to mobilize the pile duringthe re-strike tests. Hannigan and Webster (1987) suggested the following guidelinesfor dynamic testing.Minimum impact force for steel piles =Minimum impact force for concrete piles =1 < < 3In order to improve the reliability of dynamic analysis methods, Svinkins and Woods(1998) suggested the implementation of time dependent soil properties in estimating the pileresistance. They concluded that the time between static and dynamic tests has to be within ashort duration at which the time difference should not exceed 1 to 2 days. They used theratio of pile resistances obtained from dynamic and static tests as the main criterion forcomparison and correlation studies. Lo et al. (2008) stated that the advantages of using theratio are to avoid the total uncertainty in innate variability, effects of pile installation on soilproperties, prediction model, and input parameters for resistance calculation using dynamicmeasurements. This ratio is treated as a random variable, and it is characterized by the meanand the coefficient of variation (COV). The COV is calculated by dividing standard ofdeviation by the mean. Lo et al. (2008) implied that dynamic analysis methods will tend togive a conservative pile resistance in a pile design and a conservative method is notnecessary a better method from a probabilistic point of view. In addition, the degree ofconservatism of a method and its related variability should be considered when establishingstatistical resistance factors for limit state design of pile foundations.Past correlation studies of the dynamic and static tests have been performedextensively starting from 1980’s and the results are chronologically arranged and