Investigation of the effect of critical depth on the shaft resistance of closed ended piles in clay

This paper describes the results of field tests carried out using instrumented piles installed in a very soft estuarine silty clay deposit at Kinnegar, Belfast. The site has been used for a number of years as a geotechnical test bed site and has been comprehensively characterised using both numerous in-situ tests and by mean of an extensive laboratory test program. The instrumented pile used in the investigation was developed at University College Dublin and includes sensors which allow readings of both total radial stress and pore pressure during installation and load testing to be made at a number locations along the pile shaft and at the pile base. The tests were carried out to investigate the effect of pile length on the average shear stress mobilised during installation and load testing. The results are compared to other case histories reported in the literature.