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

Ratio of Final to Initial Pile Resistance95experiencing setup by a factor of 1 to more than 6 of its initial resistance estimatedimmediately after installation, while piles in a mixed profile exhibited over a range betweenthose for sand and those for clay. Although effect of soil on pile setup is apparent, necessarydata to quantitatively estimate pile setup in terms of soil properties is rarely available.Zone 1:NonlinearPile SetupRate or PoreWaterDissipationZone 2:Linear Pile SetupRate or Pore WaterDissipationZone 3:AgingTime in Logarithmic ScaleFigure 2.18: Idealized schematic of pile setup zones (after Komurka et al. 2003)For the case of piles embedded in cohesionless soils, Komurka et al. (2003) statedthat excess pore water pressure dissipates rapidly. As a result, pile setup occurs with alogarithmic linear relationship (Zone 2 in Figure 2.18) and mostly associates with aging inthe soil (Zone 3 in Figure 2.18) (Axelsson, 2002). Aging refers to a time-dependent changein soil properties at a constant effective stress. The effect of aging increases soil shearmodulus, stiffness, and dilatancy, and reduce soil compressibility (Axelsson, 1998; andSchmertmann, 1991). Research performed by Chow et al. (1998) on open-ended pipe pilesdriven into dense marine sand showed an 85% increase in shaft resistance during the intervalbetween 6 months and 5 years after installation. They concluded pile setup was caused bythe changes in the stress regimes created during pile installation and the creeping effect