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

128borehole such that the piezometer and the flat pressure surface faced the flange of the testpile. Measurements were taken every 4 seconds during pile driving, restrikes and SLT, whilereadings were taken at 30-minute intervals between restrikes as well as between the lastrestrike and SLT. The push-in pressure cell denoted as PC1 in Figure 3.3 (a) was installedapproximately 7 m (23 ft) below the ground surface and 200 mm (0.65 ft) away from theflange of ISU5. Given the deep water table (11 m or 36 ft)) encountered at ISU5’s site, PC1was installed above the water table (i.e., at 7 m or 23 ft) to avoid damage to the connectionbetween the top of the pressure cell and the drilling rod during installation and retrieval aswitnessed previously. For ISU6 shown in Figure 3.3 (b), two push-in pressure cells (PC3 andPC4) were installed below the GWT at approximately 10 m (33 ft) below the ground surfaceand 230 mm (0.75 ft) and 610 mm (2 ft) away from the flange, respectively. Given that ISU6was the last test pile driven in a cohesive soil profile, a higher risk was taken to measure thedissipation of pore water pressure at a deeper location. Due to the space limitation, only thepore water pressure measurements are included in this paper and completed measurementsare reported in Ng et al. (2011a).3.4.5. Pile driving and restrikesSingle-acting, open-ended diesel hammers were used to drive and restrike all testpiles as summarized in Table 3.3 and to install all reaction piles. Before driving each testpile, two 18.3 m (60 ft) long HP 250×63 (HP 10×42) reaction piles were driven by aligningtheir webs as shown in Figure 3.6. To avoid the effect of reaction pile installations on soilproperties initially measured at the test pile location, the reaction piles were installed at anequal distance of 2.44 m (8 ft) on both sides of the test pile (see Figure 3.6 (a)) except forISU6 (see Figure 3.6 (b)), in which case reaction piles were installed at distances of 1.73 m(5.7 ft) and 3.12 m (10 ft) on either side of the test pile as another test pile (ISU7) wasincluded with a shallower embedded length of only 5.8 m (20 ft). In all cases, the reactionpiles were installed with an exposed length of 1.8 m (6 ft) to connect them with a horizontalreaction beam. The test pile was then driven and the PDA data were recorded during bothpile driving and restrikes. To help with pile setup evaluations, the time and the pile