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

942.8.2 Effect of pileIt was reported by Camp and Parmar (1999) with focus on a stiff, overconsolidatedcohesive calcareous soil that a displacement pile (such as a closed-ended pipe pile), whichexerts greater disturbance to the surrounding soil than a low displacement pile (such as asteel H-pile), takes a longer time to fully gain its resistance (i.e., a slower setup rate).However, based on a database of pile static load and dynamic tests collected from literature,Long et al. (1999) found no clear evidence of difference in setup time between largedisplacement and low displacement piles driven into mixed and clay soil profiles. A reportby Finno (1989) indicated that a closed-ended pipe pile generated higher excess pore waterpressure than steel H-pile; however, the unit shaft resistances for both pile types matchedafter 43 weeks. It is anticipated that pre-stressed concrete piles exhibit larger setup than steelH-pile, which is due to a higher coefficient of friction along the soil-concrete pile interface asreasoned by Priem et al. (1989). Furthermore, more permeable wooden piles, which absorbwater and allow faster dissipation of pore water pressure, have higher setup rate than otherless permeable piles (Bjerrum et al., 1958 and Yang, 1956).2.8.3 Effect of soilMany research outcomes have confirmed the effect of different soil types on pilesetup. Occurrence of pile setup has been recognized in both cohesive and cohesionless soils.In cohesive soils, Komurka et al. (2003) qualitatively explained that excess pore waterpressure dissipates slowly and dictates the pile setup rate, which moderately relates tologarithmic nonlinear relationship (Zone 1), mainly relates to logarithmic linear relationship(Zone 2), and slightly involves aging mechanism (Zone 3) shown in Figure 2.18. Randolphet al. (1979) stated that the variation in soil stress around a pile after installation isindependent of the soil’s overconsolidation ratio (OCR). However, Whittle and Sutabutr(1999) indicated that reliable pile setup estimations for large diameter open-ended pipe pilesdepend on accurate measurement of OCR value and hydraulic conductivity. Compiling pileload test information published in literature, Long et al. (1999) found that piles embedded insoft clays experience more setup than in stiff clays. They noticed piles embedded in clay soil