A laboratory investigation of the effect of flow rate and bedding characteristics on the interaction of a vertical water jet with an idealised soil medium

Water conveyed through pipes systems installed beneath the ground surface has become standard practice in which treated fresh water is transported to communities. This kind of water delivery is successful in many regards but also results in considerable amounts of water wastage in the form of undetectable leakage. This is a serious concern since fresh water reserves throughout the world are being depleted faster than it is replenished; yet, there exists a large gap in understanding how leaks outside water distribution pipes behave. Recent studies that have investigated external leakage behaviour have discovered that when water under pressure passes through a leak opening (orifice); a water jet is formed, which interacts with the surrounding soil (bedding material) in a manner that causes the granular medium to fluidise. This fluidisation process was seen to exhibit complex behaviour, which restricted shallow leaks under relatively high pipe pressures from growing and reaching the bed surface. As a result, leaks are able to remain bound beneath the ground surface with reduced chances of being detected and repaired. The goal of this study was to conduct experiments aimed of performing a sensitivity analysis on how leakage conditions in the bed are affected when soil-leak characteristics including jet flow rate, bed height and the size of the granular particles in the bed are varied. In this study a vertical water jet in an idealised granular bed (glass beads) was used. The leakage conditions that were examined for each soil-leak factor comprised of measuring the height of the fluidised region and distributions of pore pressure, fluid velocity and energy within the bed. The sensitivity analysis was based on data collected from experiments, which were conducted using an apparatus that was able to simulate an unbound pipe leak. The apparatus comprised of a glass tank, which housed the bedding material. An orifice installed at the bottom of the tank assisted in creating the water jet required for the pipe leak and, a Pitot tube positioning system above the tank allowed for positioning of straight and L-type Pitot tubes in the granular bed, which were used to measure the leakage conditions within the bed. Results from the experiments revealed that the soil-leak factors, which were investigated had significantly affected leakage conditions, each to varying degrees. Larger jet flow rates led to an exponential increase in fluidisation height and higher maximum pore pressures, velocities and energies were measured in the bed. It was found that by varying the bed height, fluidisation height increased linearly with decreasing bed height and only the pore pressure distribution was considerably affected, where larger maximum pore pressures were measured in beds that were shallower. The effects of varying particle size included lower fluidisation heights and maximum pore pressures in beds that contained larger particles. Interestingly, the velocity and energy distribution remained substantially unaffected