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

1323.5.3. Logarithmic trendWhen plotted as a function of time (t), the percent increase in total resistance, shaftresistance, and end bearing with respect to the corresponding resistance at EOD (∆R t /R EOD inTable 3.4) obtained using CAPWAP generally followed a logarithmic trend for ISU5 asshown in Figure 3.11 (a) & (b). Figure 3.11 (a) depicts the logarithmic trend over a shortduration immediately after EOD, and Figure 3.11 (b) confirms the same trend over a periodof 9 days. As shown in this figure, total, shaft and end bearing resistances increasedimmediately after EOD with rapid gains within the first day, followed by increase at a slowerrate after the second day. The same observation holds for the calculated total resistance fromWEAP. Furthermore, the extrapolated WEAP and CAPWAP logarithmic trends providegood estimates of the measured pile resistance from SLT. Figure 3.12 shows a similarobservation for all test piles, in which the percent increase in total resistance with respect tothe corresponding resistance at EOD from CAPWAP followed the logarithmic trend.3.5.4. Pore water pressurePore water pressures recorded using PC3 and PC4 at 10 m (33 ft) below groundsurface with the groundwater table at 4.6 m (15 ft) at ISU6 are plotted in Figure 3.13 asfunction of time. Figure 3.13 (a) shows the recorded data for the first 20 minutes period.Accordingly, pore water pressure recorded using PC3 experienced some drop in readingsbefore the pile toe reached the depth of the device. Significant change was recorded as thepile passed through the gauge location during driving. The recorded pore pressureprogressively increased from 84 kPa (12 psi) to 101 kPa (14.6 psi) at PC3 and from 55 kPa (8psi) to 64 kPa (9.3 psi) at PC4 between the time when the pile passed through the devices andBOR3. This observation is attributed to the compression of the normally consolidated (OCR= 1.1 between 9.3 m (30.5 ft) and 15.5 m (51 ft)) and sandy low plasticity clay soil duringpile installation, resulting in the subsequent increase in the pore water pressure. In addition,the sandy low plasticity clay layer in which the PCs were installed has a small measuredhorizontal coefficient of consolidation (C h ) of 0.008 cm 2 /min (0.0013 in 2 /min) (see Table3.1), which delayed the dissipation of pore water pressure. After BOR3, fluctuations in data