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The physical and chemical effects of bacterial biofilm formation upon hydraulic conductivity, mineral-solution interactions and the formation of biogenic mineral precipitates have been studied over a wide range of scales, from microscopic to macroscopic. Several novel pieces of equipment have been designed, constructed and commissioned in order to measure the physical effects of biofilms upon fluid flow through fractures and porous media, the overall effects of biofilm formation upon mineral surface reactivity, and the imaging and identification of mineral precipitates formed due to the presence of biofilm and bacterial cell surface polymers on a quartz surface. This paper presents an overview of key experimental methods and selected results; further experimental information is being published elsewhere.Biofilm formation within quartz sand in artificial groundwater resulted in a two orders of magnitude reduction in hydraulic conductivity under bench-scale constant head conditions. However, under quasi-environmental conditions within macroscopic centrifuge experiments, a reduction of 21% was measured, revealing differences in measurements and, hence, the value of the macroscopic experimental work in scaling from micro to macro.

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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.