Study On The Characteristics Of Mud And Sand Depositon In Submerged Pipe After The Dam Was Built On Xiangjiang In Changsha

As an important urban infrastructure, drainage systems play an important role in the long running process, but sediments in drainage pipes have been continuously deposited will reduce the hydraulic section area, i ncrease flow resistance, leading to significantly reduced pipeline capacity. When sediments are deposited to a certain extent causes the drainage pipe blocked, affect the operation and regulation of urban drainage pipe system.The high-ranked culvert buried under the Nanhu road is the main drainage network of the south of the upper zone of the Nanjiao Park Area. The present situation of the network is that the culverts(4m×3m boxes) are lying along Xueyuan Road and Shuichang Road.After the damming of the Xiangjiang River, The original free flow in the pipe network culvert changes into a submerged flow, due to its culvert bottom elevation below the normal water level, which will lead to the present network overflow especially when it rain in those areas. If t his problem cannot be solved, we do believe that this overflowing condition will inevitably lead to a great economic loss.In order to solve these problems, this study uses the theoretical formula of deposition of sediment movement and Ackers-White formulas.The equations of the velocity when the particles start to move,suspend and stop were gotten from the rule of silt sediment movement. The velocity with no depositing was gotten from a equation of silt sediment movement in drainage. And the relation betwee n these velocity was analyzed at last to determined the self-cleaning velocity in this study.Using computational fluid dynamics(CFD) commercial software FLUENT as the simulation platform, Simulated mud and sand deposition rule of submerged outflow pipe, the results showed that: according to the heavy rain, moderate rain, light rain do in three operating conditions of the comparison,rainfall effects on the deposition of suspended matter is small, but great influence on the sand deposits. And with a reduction in rainfall, culvert reached upon clearance flow in bottom sediments gradually increasedSimulated results on the three conditions of mud and sand facies sedimentary thickness to be cumulative, obtained under different rainfall intensities, silt sedimen t thickness per unit rainfall. Synthesizing the current rainfall data for many years in Changsha, and accumulate silt sediment thickness in different seasons to determine the pipeline dredging cycle.Based on a comprehensive comparison of existing domestic and international dredging technology, and the consideration of the existing dredging technology in Changsha City, Dredging channel was decided to be used. A new pipeline was set in the effected area in order to form a double-pipeline. And set valve to dredging pipeline. In a submerged outflow pipe culvert upstream at the appropriate location, set the horizontal flow type grit Chamber,use mechanical equipment to regularly clean up the grit in the mud and sand. CFD simulation results shows that: Horizontal flow type grit Chamber sand-removing effect better, it can achieve the desired removal effect.