Enhancement of Shaft Capacity of Cast-in-Place Piles Using a Hook System

Abstract

This research investigates an innovative approach to improve the shaft bearing capacity of castin-place pile foundations by utilizing passive inclusions (Hooks) that will be mobilized if movement occurs in pile system. An extensive experimental program was developed to study the shaft bearing capacity of cast-in-place piles with and without hook system in soft clay and sand.First phase of the experiment was developed to investigate the effect of passive inclusion on pilesoil interface shear strength behaviour, employing a modified direct shear test apparatus. The interface strength obtained for pile-soil specimens was found to significantly increase when passive inclusions were implemented. Apparent residual friction angle for concrete-sand interface increased from 22 to 29.5 when two hook elements were used at the pile-soil interface. The pile-clay apparent adhesion was also increased from 19 kPa to 34 kPa.A series of pile-load testing at field were performed on cast-in-place in soft clay to investigate the effect of passive inclusions on pile bearing capacity. The pile-load tests were conducted at Gloucester test site. Four model piles were cast with steel cages along with hooks (P1-no hook, P2-7 hooks, P3-5 hooks and P4-5 hooks) installed on the exterior side of the steel cages prior to filling the hole with concrete. Results from these tests show a proportional increment of friction resistance compared to the number of hooks installed, also compared with those obtained using traditional pilling system (without hook). The interface apparent adhesion for concrete piles sheared against clay under static load test conditions increased about 38% when 5 hooks were installed at the surface of the concrete. *Patent Pending III ACKNOWLEDGMENTS