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

133due to restrike and SLT as well as graduate dissipation of pressure with time were generallyseen (Figure 3.13 (b).For PC3 that was closer to the pile, the pore water pressure dissipation generallyfollowed a logarithmic trend and reached a value of about 68 kPa (10 psi) within a day (i.e.,around BOR5) and almost its hydrostatic state, which indicates complete dissipation in aboutseven days (i.e., around BOR7). Re-plotting the dissipated PC3 pore water pressure inpercentage of the pressure measured at EOD (93 kPa) as function of time (t), Figure 3.14confirms the logarithmic trend with a relative high coefficient of determination (R 2 ) of 0.79.The minimal difference in the gradients of the logarithmic best fits (i.e., 0.55 for resistanceand 0.50 for pore water pressure dissipation in equations included in Figure 3.14) suggeststhat the logarithmic increase in total pile resistance followed the rate of the pore waterpressure dissipation. The difference between the increase of pile resistance curves and thepercent of pore water pressure dissipation curve, which is mainly due to the difference in theintercept values of 0.33 for resistance and 0.25 for pore water pressure as shown by equationspresented in Figure 3.14, is believed due to remolding and healing process occurring in thesoil disturbed by pile driving. With a lesser influence from pile installation, the PC4 porewater pressure reduced to the hydrostatic pressure within a day.3.5.5. Influence of soil propertiesSince the pile setup largely increases the shaft resistance, a detailed correlation studybetween soil properties and percent increase in shaft resistance (∆R/R EOD ) was performed.The percent increase in shaft resistance calculated for ISU5 using CAPWAP between EODand the last restrike is plotted along the embedded pile length in Figure 3.15 together with themeasured vertical coefficient of consolidation (C v ) and SPT N-value. A similar distributionof ∆R/R EOD for the SLT, the percent difference between the measured shaft resistance fromSLT at 9 days after EOD, and the CAPWAP calculated shaft resistance at EOD are alsoincluded in Figure 3.15 for comparative purposes. It is interesting to note that thedistributions of the percent increase in shaft resistance (∆R/R EOD ) for both CAPWAP and