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

Abstract

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 quantitative engineering units during the process. The research, undertaken in the field and using a 500 gTonne geotechnical centrifuge, investigates the validity of applying the principles of the WAK (wave-activated stiffness [K]) test analysis to monitor the progress of compaction, allowing the process to be halted once the required degree of improvement has been reached. The analytical procedures underpinning the interpretation of the compaction process data in the time and frequency domain are presented, including the derivation of dynamic stiffness, depth of compaction, and damping factors associated with the combined footing/soil system. The methods of instrumentation and data acquisition are described for both field and centrifuge test programmes, along with the procedures adopted for real-time signal conditioning and data recognition. The results of the field and centrifuge test programmes are discussed, and conclusions are drawn on the effectiveness of the compaction process, confirming the validity of the WAK test analysis in the prediction of improvement in soil stiffness with increasing number of blows.

Dynamic Soil Stiffness Between WAK, SASW and SCPT Tests

“…The stiffness of the soil is obtained by considering the soil to be vibrating as a single degree of freedom (SDOF) system. The most important feature of this test for the design of foundation is that, although essentially a dynamic test, the excitation and the free-body response are of such low frequency that the output may be used to predict the static-output relationship and the transfer function will be independent of the magnitude of the input [10]. Moreover, Briaud and Lepert [4] showed that an analysis of the force and velocity signals using the fast Fourier transform provides a good estimate of the stiffness of the footing-soil assembly.…”

“…The accelerometers were chosen instead of geophones in these tests. This is because the geophones were not appropriate for detecting the change in stiffness due to the high accelerations generated by impulsive forces as recommended by Merrifield and Davies [10].…”

Assessment of rapid impact compaction for transportation infrastructure applications

“…RIC is a compaction method that uses impact forces to density loose, granular soils (Allen 1996;Braithwaite and du Preez 1996;BRE 2003;Kristiansen and Davies 2004;Miller 2005;SAICE 2006;Serridge and Synac 2006;Simpson et al 2008;Watts and Charles 1993;Woodward 2005). This process has been called by other names including low energy dynamic compaction (Allen 1996;Merrifield and Davies 2000;Merrifield et al 1998;Parvizi 1999Parvizi , 2006Parvizi , 2009Parvizi and Merrifield 2000) and high speed dynamic compaction (Neilson et al 1998).…”

“…Although the majority of studies into RIC have involved field investigations, laboratory modeling of the RIC method utilizing a geotechnical centrifuge has been performed (Merrifield et al 1998;Merrifield and Davies 2000;Parvizi 1999;Parvizi 1999;Parvizi 2006;Parvizi 2009;Parvizi and Merrifield 2000).…”

“…Research was conducted in the field and the laboratory using a geotechnical centrifuge. Merrifield and Davies (2000) This document describes work undertaken to evaluate a prototype high speed dynamic compactor (RIC). The work reported was intended to implement a monitoring system for the machine to provide an indication when optimum compaction had been achieved.…”