Experimental Study on Submerged Sand Erosion through a Slot on a Defective Pipe

A physical model study was conducted to examine the development of submerged sand erosion through a slot on a defective sewer pipe. Various parameters that affect the erosion process were studied, including particle size, defect size, position on the pipe, and water depth. This experimental study used particle image velocimetry analysis to provide a deeper understanding of the mechanism of sand erosion due to defective sewer pipes. The sand velocities were determined, and the sand and water flow rates were measured. After the erosion process was initiated, the sand and water outflow rates quickly reached the steady state until the eroded zone reached the slot opening. During the steady erosion process, the region of sand motion was restricted to a narrow zone above the opening, with sand particles sliding into the newly formed cavity at the angle of repose. An increase in slot width significantly increased the sand and water flow rates. A decrease in sand particle size from medium to fine resulted in a decreased sand flow rate mainly due to decreased water flow. An increase in sand particle size from medium to coarse resulted in a decreased sand flow rate due to the arching resistance close to the slot for larger sand particles. In this study, the sand flow ceased when the ratio between the slot width and particle size was less than 3.1. The ratio between the sand and water flow rates was found to be a function of the ratio of slot width to particle size. The water level above the pipe and the slot position affected the sand and water flow rates. A simple analytical model was developed to estimate the sand and water flow rates in the erosion process. (C) 2017 American Society of Civil Engineers.