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

255Liang (2000) calculated an average shaft quake of 1.27 mm and toe quake of 3.18mm, based on SPT tests collected and reported by Goble, Rausche and Likins (GRL) throughthe default CAPWAP signal matching procedure. Using these quake values, Liangdetermined the damping factors through a number of consequent iterations using WEAP untilthe estimated SPT blow count matched the actual recorded SPT N-value at each soil layer forall 23 Ohio Department of Transportation piling project sites. Performing the defaultCAPWAP signal matching procedure on 34 driven test piles (31 pipe piles and 3 H-piles) atthe 23 test sites, Liang independently determined the damping factors and compared themwith those estimated using WEAP on SPT. The estimated damping factors obtained fromWEAP in this manner for all sites were adjusted by a reduction factor, so its average valuewas close to the CAPWAP average value as illustrated in Table 7.3 for both 60 and 70% SPThammer efficiencies. Finally, the correlations between the adjusted damping factors (shaftand toe) and the corresponding SPT N-values generated Eqs. (7.3) and (7.4) for clay andsand, respectively. The validation of these proposed equations has not been provided. Thus,they have not been widely implemented for practical applications.( ) (7.3)( ) (7.4)Recognizing the limitation with the current CAPWAP analysis, Roling (2010)proposed a displacement-based signal matching procedure using a commercial finite elementanalysis program SAP2000 (Computers & Structures, Inc. 2008). Similar to the onedimensionalsoil-pile model used in CAPWAP as shown in Figure 7.1, the pile topdisplacement was generated using SAP2000 and compared with that measured using thePDA. As a result of this proposed matching procedure, the shaft damping factor wasdetermined to be directly proportional to pile installation depth, whereas the shaft quakevalue decreased with the depth on account of the increasing geostatic pressure. Furthermore,Roling concluded that the magnitude of the damping factor was dependent upon the stage of