Hydraulics & Waterways

Oral

397322 - Modeling soil loss by water infiltration through sewer pipe defects

Thursday, June 7
8:30 AM - 10:00 AM
Location: Greenway CD
Co-Authors: David Zhu, Edmonton, Alberta, Canada – University of Alberta; Dave Chan, Edmonton, Alberta, Canada – University of Alberta

Due to the deterioration of sewer pipes, soil loss due to water infiltration through pipe defects may result in ground collapses and/or the formation of urban sinkholes. In this paper, sand flow under the influence of water is studied using a numerical model. Soil particles without cohesion are simulated using a coupled discrete element model incorporating fluid flow and Darcy’s Law is used to account for soil/water interaction. The parameters in this numerical model are calibrated based on physical experiments. From the numerical results, soils above the pipe defect will be eroded by water flow in a narrow zone just above the pipe defect, and the width of the erodible zone is proportional to the size of the defect. Based on analysis of the force chain between soil particles during the erosion process, it is found that soil particles close to the pipe defect are driven under the action of gravity and drag forces from the fluid, whereas the friction between soil particles has a negligible effect on particle motion. From the variation of soil flow rate in the erosion process, soil particle size and pipe defect size are the two dominant factors controlling the rate of flow of the soil which is proportional to the water flow rate. Based on the free-fall arch theory, an analytical model has been developed incorporating Stokes law to account for the water flow. The analytical model is verified by comparing it with physical and numerical modeling results. The mechanism of soil loss due to defective sewer pipe is investigated in this numerical simulation, and the proposed analytical model provides an effective approach to estimate the soil flow rate in the erosion.

Yao Tang

University of Alberta

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