Estimation of Pile Setup and Incorporation of Resistance Factor in Load Resistance Factor Design Framework

Soil setup is defined as the increase in axial resistance of driven piles after end of driving (EOD). Very recently, over the last five years, the time-dependent increase in axial resistance of prestressed concrete piles (PSC) driven into mainly cohesive soils of Louisiana, due to setup, was systematically quantified using measured field tests. Based on the collected data of thirty PSC test piles (TP) during driving and following load tests, it was observed that soil setup is significant and continues to develop for a long time after EOD. This study will first present the development of analytical models to estimate soil setup after EOD followed by a procedure to determine the resistance factor of a pile setup in accordance with the load and resistance factor design (LRFD) methodology that targets a specific reliability index. The analytical models were developed from 70 clayey soil layers of twelve instrumented test piles. The soil setup resistance was predicted using the developed analytical models at four different time intervals (i.e.,30, 45, 60, and 90days) after EOD in order to perform the LRFD calibration. The calibration was performed using the first order second moment (FOSM), first order reliability method (FORM), and Monte Carlo simulation (MCS) method on thirty test piles (i.e.,twelve instrumented test piles and eighteen noninstrumented test piles). The statistical database showed that log-normal distribution can be used to properly describe the probabilistic characteristics of predicted setup resistance by the developed analytical models and the resistance factor was calibrated with a target reliability index, , of 2.33. The calibration showed that the resistance factor due to soil setup was 0.35.