Analysis of Negative Skin-Friction on Single Piles by One-Dimensional Consolidation Model Test

The computer program pile negative skin friction (PileNSF) was developed by the authors to predict the bearing capacity of a pile embedded in a consolidating ground due to surcharge loading. The program uses a one-dimensional analytical soil-pile model, which was formulated based on the nonlinear load-transfer method and Mikasa's generalized one-dimensional consolidation theory. To investigate the development of negative skin friction on single piles, as well as to validate the computer program (PileNSF), a laboratory model test was performed in this study. The clay layer was subjected to increasing surcharge loads to simulate actual field conditions. Results showed that as excess pore pressure decreases and as surcharge load increases, the dragload and downdrag on pile increases. The measured values of soil settlement, excess pore water pressure, and axial force on pile were compared with the predicted values obtained from the computer program. The results of the computer program (PileNSF) showed to be in good agreement with the measured data. Therefore, negative skin friction on single piles can be effectively predicted using the computer program, PileNSF, provided that reasonable parameters are used in the analysis. After validating the program, a parametric study was carried out to study the influence of various pile design parameters on negative skin friction.