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

1213.2. IntroductionMany researchers and practitioners have recognized the increase in resistance (orcapacity) of driven piles embedded in cohesive soils over time, and this phenomenon isreferred to as pile setup. The mechanisms of pile setup are related to the healing of remoldedcohesive soils, the increase in lateral stresses, and the dissipation of pore water pressure(Soderberg 1962 and Randolph et al. 1979). When accounted for accurately during design,the integration of pile setup can lead to more cost-effective design as it will reduce thenumber of piles and/or pile lengths. Unfortunately, experimental data required for detailedpile setup studies rarely exists.Static or dynamic tests can be performed to evaluate pile setup; however, it is notfeasible in practice to perform these tests over a period of time as acknowledged in theinterim report by the American Association of State Highway and Transportation Officials(AASHTO) (2008). Empirical methods to estimate pile setup have been proposed by severalresearchers, such as Pei and Wang (1986), Skov and Denver (1988) and Svinkin and Skov(2000). However, these methods have several shortcomings. For instance, Pei and Wang(1986)’s method was purely empirical, specifically developed for Shanghai soil, and lack ofgeneralization in terms of soil properties. Skov and Denver (1988)’s and Svinkin and Skov(2000)’s methods require inconvenient and costly restrikes for the estimation of pile setupfactors, and lack of generalization in terms of soil properties. Due to insufficientexperimental data, these methods have not been substantially validated for accurate practicalapplications. For these reasons, empirical methods have not been included as part of theAASHTO (2008) LRFD Specifications to account for pile setup.To account for pile setup in the LRFD approach, the followings are needed forcommonly used foundation types: a) sufficient and detailed dynamic and static field test dataas a function of time for accurate pile setup evaluation; b) detailed subsurface investigationsand monitoring of soil stresses to quantify pile setup (Komurka et al. 2003); and c) asystematic reliability-based method to account for pile setup in the LRFD approach.