Segregation in High Concentration Flows

Sand injectites are observed in a wide range of locations and settings, both modern and ancient but little is known about the processes controlling their formation. The scale of these injections range from mm to km in size and represent the forceful injection of fluidised sand into host strata. Due to the difficulty of observing in-situ events and relative paucity of outcrop data interpretations, understanding of the flow processes during fluidisation pipe formation is lacking. Existing fluidisation models provide mechanisms for fluidisation but remain simplistic and do not capture the full dynamics nor the range of characteristics which are observed to vary both spatially and temporally across the system during the formation of sand injectites. Fluidisation theory relies on an understanding of both the velocity characteristics and the concentration characteristics of a fluidisation event but comprehensive evidence of these quantities has not previously been available. The novel application of experimental techniques in both two dimensions and three dimensions in this thesis provides both high resolution velocity data for the formation and quasi-steady state of fluidisation pipes along with high resolution concentration data for the first time. Complementing this, the novel application of numerical modelling provides insight into the early stages of void formation and demonstrates a new methodology for investigating flow processes during fluidisation. The products of the fluidisation events modelled are presented providing a direct link between fluidisation processes and products for reference in interpreting outcrop data. Residual morphologies are evidenced resulting in explanations of the poor detection rate of sand injections. New models of fluidisation and void formation are presented based on the extensive characterisation of a fluidisation event achieved across multiple methodologies.