Influence of pile plugging on skin friction in overconsolidated clay

Field tests were conducted to investigate the influence of the method of installation and degree of soil plugging on the skin friction developed along displacement piles subjected to static axial loading in overconsolidated clay. The study was conducted at the National Geotechnical Experimentation Site at the University of Massachusetts in Amherst and included the installation and testing of 44 pipe piles with diameters ranging from 60 to 168 mm and embedment lengths ranging from 1.5 to 10.7 m. The methods of pile installation included both driving and jacking. Some piles were installed with 60 degrees apex cone tips while others were installed open ended. Results of the test program indicated that the method of installation had a significant influence on the amount of soil plugging in open-ended piles. In addition, it was found that the pile installation method and degree of plugging significantly affected the resulting axial compressive skin friction. It is suggested that the plugging effect on skin friction results from differences in lateral stresses that develop along pile shafts, while the effect of the installation method is related to installation disturbance. An effective stress method of analysis is proposed for estimating ultimate pile skin friction taking into consideration the influence of installation method and plugging on pile capacity.