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

342.3.8. Interpretation and calculation of PDA resultsGoble and Likins (1996) suggested that final PDA results interpretation should beperformed by qualified engineers who understand wave propagation concept, Case method,pile design, and pile driving. Soil resistance effects on pile can be evaluated qualitativelyfrom the force and velocity records. Noted that the velocity record has been multiplied bythe pile impedance Z, and it is plotted together with the force record. Figure 2.5 illustratesthe pile responses induced by various soil resistance conditions. The pile loading sectionhappens between the time of impact when the first peak of both force and velocity recordsoccur and the time at 2L/C. The unloading section occurs after the time 2L/C. Theseparation between the force and velocity records between the time of impact and the time2L/C represents the shaft resistance, and the toe resistance is identified at the time 2L/C.Figure 2.5(a) shows a minimal separation between force and velocity within theloading section. The velocity peaks and the force decreases to negative at the time 2L/C.These typical responses indicate that only small shaft and toe resistances acting on the pilewhich is similar to a free end rod as described in Section 2.3.3. Within the unloading section,the force increase from negative to positive value and rises above the velocity record thatdecreases from positive to negative value. Similar to the loading section, the smallseparation between the force and velocity records show a small shaft resistance on the pile.Figure 2.5(b) shows a similar response as observed in Figure 2.5(a) at the loading section.However, the force increases and velocity decreases significantly at time 2L/C, indicating asmall shaft resistance and a large toe resistance on the pile. At the unloading section,because of high toe resistance, the force continues above the velocity before a dissipation ofthe force. In contrast, Figure 2.5(c) shows a large separation between the force and velocityrecords during the loading section. These typical responses show that the pile has a largeshaft resistance, and a similar observation is noticed in the unloading section. Detailedinterpretation of the PDA results can be referred to Hannigan et al. (1998) and Hussein andGoble (1987).