Image-Based Measurements to Estimate Bearing Capacity of Hollow Driven Piles Under Impact Loading

Abstract

Hollow driven piles are long, slender columns made of concrete or steel and have a predetermined shape and size. They are installed by driving, jetting, screwing, jacking, vibrating, drilling, and grouting, or a combination of them. When a hollow pile (open-ended) is driven into the ground, a soil plug may develop within the pile during driving, which may prevent or partially restrict additional soil from entering the pile. It is known that the driving resistance and the bearing capacity of open-ended piles are governed largely by this plugging effect. Particle Image Velocimetry (PIV) technique has been adopted to understand pile-soil interaction during the installation of piles and to determine the effect of plugging on load-carrying capacity of piles. Experimental studies have been performed in a steel tank of dimensions 600 mm × 200 mm in plan and 450 mm deep. The top central part of front side of the steel tank is made of perspex sheet to facilitate image capture. Half section hollow aluminum piles modeled using wood’s scaling law is used in the experiments. The infill material is cohesionless sand with different densities and impact load has been applied to drive the piles. Under axisymmetric conditions, the impact load is applied on the pile, and failure pattern at the interface region is captured using a high resolution digital camera that is later analyzed through Geo-PIV software. The number of blows required to drive the pile and rate of plugging induced is measured. The strain contours around pile-soil interface obtained through image analysis clearly indicated the effect of infill on pile driving. Bearing capacity of the hollow pile is estimated using three different methods, viz., IS 2911 (2010) SPT-based formula, American Petroleum Institute (API)’s design criteria, and SPT-based empirical equations proposed from literature. It is seen that SPT-based design method considering the plugging behavior gave a better estimate of bearing capacity values.