Water and sediment characteristics in pressurized pipelines under complex terrain conditions

This study selects the pipelines of the SGN as the research object and combines the experimental study with numerical simulation to investigate the water and sediment characteristics in pressurized pipelines under complex terrain conditions and determine the critical non-silting velocity under different flow rates. The results show that the sediment concentration and particle size gradually settle along the length of the pipeline, and the sediment particle size at the sampling position is 0.724–180 μm, with a sediment concentration ranging 1.09–6.28 kg/m3. The sediment in the inverted siphon pipeline is susceptible to siltation mainly at the bend below the rising section and the rising section. The sediment concentration in the radial direction of the pipeline is smaller at the upper layer and larger at the lower layer. As the flow rate increases, the sediment concentration in the lower layer of the horizontal section of the inverted siphon gradually decreases, while that in the lower layer of the descending and ascending sections gradually increases. Excess sediment concentration at the bottom of the pipeline under low flow conditions makes the high-velocity zone move upward. The flow velocity decreases in the lower layer and increases in the middle and upper layers. The critical non-silting velocity of sediment in the pipeline under sediment particle size of 1–500 μm is 1.20 m/s. The time-averaged pressure in the pipeline under water-sediment conditions is slightly greater than that under clear water conditions. The increase in sediment concentration at the bottom of the pipeline causes the fluctuation frequency and amplitude of pulsation pressure at the section center of the pipeline to be uneven and the frequency more dispersed. The research results may provide reference for the operation and design of similar projects.