Analysis and calculation of scour critical velocity of suspended particles in a storm sewer.

The suspended particles in storm sewer can be easily washed away and migrated. However, few studies analyzed the scouring state of suspended particles in pipelines, and also, there was a lack of quantitative calculation. This study simulated the scouring process of suspended particles in a storm sewer with different pipe materials, and mathematical models were built for the scour critical velocity. The results showed that with the increase of particle size, density and the roughness of the pipe wall, the scour resistance of suspended particles increased, and the scouring rate decreased; therefore, the corresponding scour critical velocity increased. In accordance with the scouring rates of quartz sand and zeolite at different flow velocities in the storm sewer, the scouring state of the suspended particles could be divided into three types: no scouring, minor scouring, and massive scouring. The scour critical velocity ranges of quartz sand and zeolite with two densities in four kinds of pipes were determined, and mathematical models for the scour critical velocity of suspended particles were established. After verification, the difference rate between the calculated values and measured values was in the range of -10.56% to 6.63%, and the two values had good consistency. PRACTITIONER POINTS: Scour resistance of suspended particles increases with particle size or density. The smaller the roughness of the pipe wall, the higher the scouring rate. Higher flow velocity leads to a higher scouring rate. As scouring rate rises, no scouring, minor or massive scouring occur in sequence. Difference between the calculated and measured values is from -10.56% to 6.63%.