Laboratory experiments evaluating sedimentation and mound formation of obliquely discharged sand particles in stagnant water

Abstract

Many parameters are involved in the deposition of a known mass of sand particles discharge from oblique pipes used in a range of engineering applications. Existing knowledge is not sufficient to accurately predict sediment mound dimensions and development from vertical and horizontal pipes. To better understand deposition patterns, laboratory experiments were done to investigate the development of subaqueous sand deposits from oblique pipes in stagnant water. Factors including nozzle diameter, release angle, release height, and sand mass were evaluated. It was found that nozzle size plays the most important role in shape formation and mound development. Release angle and release height were secondarily important. Five different shape patterns were observed and denoted as circular, ellipse, circular-ring, ellipse-ring, and pear-shaped. The scour hole diameter in the middle of the sediment mound was predicted using engineering assumptions and available semi-empirical correlations from the literature. It was found that the existing formulations can accurately predict the size of the scour hole for large release angles (θ = 60°). An aspect ratio of L/do was defined to combine the effect of nozzle size, do, and sand mass where L is the equivalent length of sand particles in a pipe. It was found that the mass balance equation can predict the deposition for L/do < 100. For higher aspect ratios, semi-empirical formulations were developed to predict the deposition length, width, height, and area with ±10% error.