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

261figure, a power relationship in Eq. (7.7) was established satisfactory to quantify the J s valueas indicated by a relative high coefficient of determination (R 2 ) of 0.83. Furthermore, thesedata points followed the relationship given in Eq. (7.3) suggested by Liang (2000), whichfurther reinstated the direct relationship between the J s value and the SPT N-value, asopposed to the constant values suggested by Smith (1962) and Hannigan et al. (1998) givenin Table 7.1.( ⁄ ) ; for EOD (7.7)Besides using the damping factor, the damping coefficient (c s ) as described in Section7.2 can be directly implemented in CAPWAP to define the dynamic characteristic of the soilpilesystem. Referring to Eq. (7.2), Smith (1962) defined the damping coefficient as aproduct of damping factor (J s ) and its corresponding static soil resistance (R s ). Using thedata points plotted in Figure 7.8 for EOD, the correlation between c s and the SPT N-valuewas plotted in Figure 7.9 (represented by the circular solid markers). Similarly, dampingcoefficients as tabulated in Table 7.4 were estimated based on Liang’s (2000) proposed Eq.(7.3) for J s value. Next, average damping coefficients were computed and plotted againsttheir respective SPT N-values in Figure 7.9 (represented by asterisk marks). Comparing thetwo best fit lines for the EOD, the higher R 2 value of 0.82, based on the proposed Eq. (7.7),versus the R 2 value of 0.79, based on Liang (2000), suggests that they are comparable.Similar to the aforementioned correlation study between J s and SPT N-value, theaverage shaft quake values (q s ) were calculated and plotted against the SPT N-values inFigure 7.10. The exponential decaying best fit line given by Eq. (7.8) with a high R 2 value of0.90 confirms the inverse relationship between q s and SPT N-value observed earlier in Figure7.7 and contrasts the constant values suggested by Smith (1962) and Hannigan et al. (1998)given in Table 7.1. Although the linear plastic spring of the soil model (see Figure 7.1) isnormally characterized using the quake value, it can also be defined in terms of soil stiffness(k s ), which is a ratio of static soil resistance (R s ) and the quake value. Transforming the datapoints plotted in Figure 7.10, Figure 7.11 shows a linear relationship between the k s valueand the SPT N-value given by Eq. (7.9). The relatively higher R 2 value of 0.96 exhibits a