Laboratory Modeling of Vibro‐Driven Piles

Abstract

TO better understand the factors influencing the driveability and bearing capacity of vibro‐driven piles, a large‐scale laboratory study was performed. The testing system consisted of a pressure chamber to simulate in situ stresses, a 4‐in.‐ (102‐mm‐) diameter instrumented displacement pile, a model vibratory driver, and a model impact hammer. The influence of soil and vibro‐driver parameters, in situ stress conditions, and restriking with an impact hammer on the performance of vibro‐driven pile was investigated. The soil parameters of interest were particle size (effective grain size of 0.2 mm and 1.2 mm) and relative density (65% and 90%). The vibratory‐driver parameters of interest were the frequency, eccentric moment, and bias weight applied to the vibrator. Based on maximum rate of penetration of the pile, an optimum driver frequency of 20 Hz was observed for the vibro‐driver‐pile‐soil system under investigation. The optimum driver frequency was not affected by the range of soil conditions, eccentric moment, and bias weight investigated. The relative density of soil has the greatest influence on the rate of penetration of vibro‐driven piles. Static and dynamic unit‐load‐transfer relationships were developed for piles driven by vibration and compared with those obtained for piles driven by impact under similar conditions. Impact‐driven piles developed higher capacity than vibro‐driven piles in medium‐dense sand (65% relative density), but the reverse was observed at 90% relative density, with vibro‐driven piles having greater bearing capacity.