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

2607.5.1. EOD condition for cohesive soils using SPTResults summarized in Table 7.4 for test pile ISU5 were selected to illustrate in detailthe relationship between the measured soil properties and the computed dynamic soilparameters at EOD along the embedded pile length. Figure 7.7 (a) and (b) show thecomparison of the SPT N-values to the computed shaft damping factors (J s ) and the shaftquake values (q s ), respectively. Figure 7.7 (a) shows a direct relationship between J s and theSPT N-value, demonstrated by the increase in J s up to 0.59 s/m at the depth of 10.39 m,where the low plasticity clay (CL) reached its maximum SPT N-value of 22 and by thedecrease in the J s value to 0.31 s/m as the SPT N-value decreased from 22 to 13 beforereaching the pile toe at 16.76 m. In contrast, Figure 7.7 (b) shows an inverse relationshipbetween q s and the SPT N-value, whereby the low plasticity clay at 10.39 m with themaximum SPT N-value of 22 had the smallest q s value of 1.02 mm. Below the 10.39 m, theq s value increased to 2.03 mm as the SPT N-value reduced from 22 to 13. Furthermore, thesefigures show the influence of soil types on the dynamic soil parameters. For instance, unlikethe CL layers indicated in Table 7.4, the first 0.82 m fill layer (silt (ML) and sandy clay(SC)), mechanically compacted during road construction, had a relative high J s value of 2.57s/m and a relative small q s value of 0.51 mm. Although the soil layer (CL and SC) near theground water table (GWT) at 10.8 m shared the same SPT N-value of 22 with the clay soillayer above it, its dynamic soil parameters (J s = 1.65 s/m and q s = 1.78 mm) were higher thanthose for clay soil (J s = 0.59 s/m and q s = 1.02 mm). These figures prove that the dynamicsoil parameters are not constant throughout the soil profile, as treated in the defaultCAPWAP matching procedure.To further expand on the above observations, the dynamic soil parameters computedfrom all test piles provided in Table 7.4 were compared with SPT N-values. To present abetter correlation with the SPT N-value, an average dynamic soil parameter was computedfrom those values corresponding to the same SPT N-value as plotted in Figure 7.8 to Figure7.11. Using these correlated data points, best-fit lines and their corresponding 95%confidence intervals were drawn. Figure 7.8 shows a plot for the J s value at the EOD as afunction of SPT N-value (represented by the circular solid markers). Using this data in this