Influence of soil setup on shaft resistance variations of driven piles: Case study

Pile foundations are frequently used in industrial projects in southwest lowlands of Iran. Although high setup of shaft resistance is usually reported in the area, no reliable formulation or guidelines are available for considering the increased capacity in design applications. Therefore, the pile design practices are usually not optimized. The main objective of this paper is presenting a site specific formulation for setup effects of a utility plant in southwest Iran in which a good database of prestressed concrete driven piles is available. Fajr-II Petrochemical site in PetZone of Mahshahr accommodating a utility plant is selected as the database of the current study. The setup factor (A) and the reference time (t0) are evaluated through processing of a relatively large database of this well-supervised piling project. As the main portion of variations of driven piles capacity with time is related to shaft, only shaft resistance variations are considered in this research. The shaft capacity variations are derived from signal matching analysis on PDA tests. Reliability of PDA tests has been confirmed through comparing with the static load test results. Influence of driving the surrounding piles on setup factor is also investigated. The results show that the average setup factor (A) and the reference time (t0) of 0.30 and 0.01 day, respectively, are proper values for estimating the long term capacity in this region. Evaluation of the results indicates that driving 8 piles around the test pile has increased the “A” factor average of 40% resultingin increase of the shaft capacity about 19% in one month and 22% in one year, in comparison with the tested piles with no surrounding piles driven.