Mechanical behaviour of a sand bed subjected to low energy dynamic compaction, modelled in a geotechnical centrifuge

This paper describes the design and operation of a unique model compactor simulating the process of low energy compaction in a geotechnical centrifuge. This study was undertaken at 20g using a tamper mass of 875 gm falling through 100mm onto a stiff aluminium target, having a mass 268 gm and a diameter of 100mm. Applying standard geotechnical centrifuge scaling laws, this simulated a field scale tamper mass of approximately seven tonnes falling through two meters onto a target having a base area of 3.14m 2 . Using the WAK Test method, developed to evaluate improvement in soil mechanical characteristics due to dynamic compaction, an estimate was obtained of the change in stiffness, damping coefficient, mass of vibrated soil and effective depth of influence with increasing number of blows. The soil dynamic response to each blow was measured by an array of accelerometers and earth pressure cells embedded in the soil mass. Analysis in the time domain of the dynamic load cell and accelerometer data showed improvement of soil mechanical behaviour per blow in terms of peak particle velocity and dynamic peak pressure against time of arrival. The rate and efficiency of improvement was clearly demonstrated by the relationship of peak particle velocity and dynamic peak pressure with blow number. Likewise the WAK Test was shown to be a reliable indicator of process success.