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

932.8. Pile Setup2.8.1 IntroductionPile setup refers to the increase in resistance of driven piles over time, especially pilesembedded in cohesive soils. When a pile is driven, the surrounding soil is displacedprimarily radially along the pile shaft and moves downward and radially below pile toe. As aresult of this pile installation process, the surrounding soil is remolded and excess pore waterpressure is generated. Randolph et al. (1979) stated that pile driving disturbs soil stress up toa distance about 20 pile radii, and the amount of excess pore water pressure can exceed theexisting overburden geostatic stress at a region within one pile diameter. A research onclosed-ended pipe piles performed by Pestana et al. (2002) revealed that the magnitude ofexcess pore water pressure decreases at an inverse relationship with the square of the distancefrom the pile. When healing of remolded soils and/or dissipation of the excess of pore waterpressure occur, effective stress of the surrounding soil increases, which increases the shearstrength and bearing resistance of the pile. Because of these mechanisms happen over aperiod of time depending on the rate of soil recovery and consolidation, the pile resistanceincreases as a function of time. Soderberg (1961) reported that the time of excess pore waterdissipation is directly proportional to the square of the pile width and inversely proportionalto the surrounding soil’s horizontal coefficient of consolidation (C h ). Because soildisturbance and excess pore water pressure generation and dissipation occur primarily alongthe shaft, it is suggested that pile setup is primarily attributed to the increase in shaftresistance (Axelsson, 2002; Bullock, 1999; and Chow et al., 1998). However, experimentresults relate pile setup to soil disturbance and pore water dissipation rarely exist.Pile setup has become an important research topic, because the successfulincorporation of setup in pile foundation designs contributes economic advantages to ourcivil infrastructure systems. A literature review on the effect of pile and soil on pile setup issummarized in the following sections. Furthermore, current methods available in literature tomeasure and estimate pile setup are described.