Experiment and fitting calculation of migration critical velocity of small-sized sediment particles erosion in rainwater pipeline

Abstract

The migration critical velocity of small-sized sediment particles was investigated through experiments under different particle sizes, pipe wall roughness, and sediment thickness. Such experiments were carried out to simulate the erosion process of small-sized sediment particles in a rainwater pipeline during rainfall. The mathematical models were established via quadratic fitting to calculate the critical velocity of migration. Results showed that small particles had powerful cohesive force, and aggregates had strong erosion resistance. So, for the small-sized particles (in the range of 0.33–0.83 mm), the smaller the particle size, the larger the critical velocity. When the pipe wall roughness was large, the ‘starting’ particle resistance was high. A large flow dynamic was needed to overcome such resistance. Thus, the critical velocity was great. The critical velocity was also large when the sediment thickness was large. The difference rate between the critical velocity calculated by mathematical models and the measured value was within the range of −3.60% to 5.33% and had good consistency. Under the research conditions, the critical velocity ranges of the four commonly used pipes; namely, plexiglass, steel/PVC, galvanized/clay, and cast iron pipes, were calculated. HIGHLIGHTS The aggregates of small particles in rainwater pipes have strong erosion resistance.; The critical velocity is great when particle size is small (d50 = 0.33–0.83 mm).; Critical velocity significantly decreases when the pipe wall roughness reduces.; Difference rate between calculated and measured values is from −3.60% to 5.33%.; The critical velocity ranges of the four commonly used pipes have been calculated.;

Keywords

• critical velocity
• erosion process
• migration
• rainwater pipeline
• sediment particles