A study of low-energy dynamic compaction: field trials and centrifuge modelling

This paper describes research into understanding the efficiency of the low- energy dynamic compaction process, and the development of a novel technique of real-time monitoring that can demonstrate soil improvement in quantitat ive engineering units during the process, The research, undertaken in the f ield and using a 500 gTonne geotechnical centrifuge, investigates the valid ity of applying the principles of the WAK (wave-activated stiffness [K]) te st analysis to monitor the progress of compaction, allowing the process to be halted once the required degree of improvement has been reached. The ana lytical procedures underpinning the interpretation of the compaction proces s data in the time and frequency domain are presented, including the deriva tion of dynamic stiffness, depth of compaction, and damping factors associa ted with the combined footing/soil system. The methods of instrumentation a nd data acquisition are described for both held and centrifuge test program mes, along,vith the procedures adopted for real-time signal conditioning an d data recognition, The results of the field and centrifuge test programmes are discussed, and conclusions are drawn on the effectiveness of the compa ction process, confirming the validity of the WAK test analysis in the pred iction of improvement in soil stiffness with increasing number of blows.