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

263relationship between the f s value and the dynamic soil parameters. Similarly, Figure 7.15(a)shows an approximate relationship between the FR value and the J s value, while Figure7.15(b) shows a more direct relationship between the FR and the q s value. All of theseobservations reveal that the difficulty with quantifying the dynamic soil parameters at theEOD condition using the CPT measured soil properties.To further expand on the above observations made using ISU5, the shaft dampingfactors (J s ) computed from all test piles in cohesive soils given in Table 7.4 were bestrepresented using FR values as plotted in Figure 7.16. As reported by Mayne (2007), low FRvalues (less than 1%) were observed in clean quartz sands and siliceous sands, whereas claysand clayey silts of low sensitivity exhibit FR values greater than 4%, and sandy silts and siltsfall in between. Figure 7.16 shows that medium to hard cohesive soils with SPT N-valuegreater than 9 exhibit larger J s values than soft cohesive soils with SPT N-value smaller thanor equal to 9. More importantly, Figure 7.16 shows that the J s values were dependent on theFR value (i.e., soil type). For medium to hard cohesive soils, the J s value decreased withincreasing FR value (i.e., from sandy silts, silts, clayey silts to clays). However, for softcohesive soils, the J s value decreased to a FR value of about 4% (i.e., from sandy silts to silts)and remained almost constant at about 0.08 s/m (0.024 s/ft) for clayey silts and clays. Toincorporate the FR value and the SPT N-value for a practical quantification of the J s value,data points presented in Figure 7.16 were plotted against a ratio of SPT N-value to the FRvalue (N/FR) as shown in Figure 7.17.( ⁄ ) ( ) (7.11)A linear relationship given by Eq. (7.11) was established to quantify the J s value, based ondifferent soil denseness and soil types. On the other hand, Figure 7.18 shows an approximaterelationship between the shaft quake value (q s ) and the CPT measured unit tip resistance (q c ).A similar observation was noticed in Figure 7.19 for the CPT measured unit skin friction (f s ).These analytical results reveal that the challenge associated with quantifying the quake valueusing CPT measured soil properties.