Semi-analytical solution for negative skin friction development on deep foundations in coastal reclamation areas

Abstract

This paper derives a semi-analytical solution to predict the development of negative skin friction, caused by the consolidation of newly filled soil, on piles in the reclamation area. The simulation of the whole consolidation process of the filled soil is realized by coupling the one-dimensional consolidation model before the pile driving with the two-dimensional consolidation model after the pile driving. The negative skin friction generated at the pile shaft during the consolidation is calculated by accounting the pile-soil interactions with the introduction of the load-transfer method. To address the dramatic changes of the pore water pressure at the initial drainage stage in the classic Terzaghi drainage boundary, the continuous drainage boundary is implemented. A semi-analytical solution to the developed model is derived and subsequently validated through the comparisons with the field tests and finite element method (FEM). A comprehensive parametric study is also conducted to demonstrate the effects of the pile installation time, the surcharge load, the consolidation time before or after piling, and the pile head load on the development of negative skin friction. The negative skin friction was found to be vastly different for piles installed immediately after landfilling and those installed close to full consolidation. To optimize construction period while reducing the negative friction on piles, the pile is better to be driven after the time t=90%TvH2Cv1. It is also observed that the surcharge load on the ground could significantly enhance the stiffness and ultimate capacity of the soil, and the workload subjected at the pile head can transfer the “negative” skin friction into the positive shearing resistance.