Study On The Influence Of Obstacles On The Flow Capacity Of Urban Drainage Pipeline

Because of-the too long use of time, nonstandard construction, lack of maintenance and mismanagement and other reasons, obstacles defect and other functional defects exists in urban drainage pipeline. The existence of obstacles will certainly change the flow of water in pipeline, evaluating the influence of obstacles on pipeline flow ability through these changes is the main content and task of the paper.Based on classical hydraulics theory, combined with drainage pipeline characteristics and current pipeline design standard, a transparent drainage pipeline device was built and four grades obstacles (two for each grade) was made to research the influence of obstacles on pipeline flow ability. The main characteristics of the whole device are easy to observe the flow state, control slope and flux and densely measure the water depth in pipe in large scale.Through the experimental phenomena observed, if there is no obstacle in pipe, the flow state of water in pine is uniform flow. After joining the obstacle, due to obstacles’ blocking effect, upstream appeared backwater phenomenon and produced a list of wave to propagate upstream until the inlet and upstream water depth continued to increase, finally, the water slopped over the top of obstacle, forming weir flow; the water fell from the top of the obstacle, depth reduced and velocity accelerated, forming rapid stream. With the increase of the flow distance, current velocity decreases gradually and in the same time, water depth increases, formats water tongue, finally, water depth restored to the state of no obstacle of water depth in front of the pipe outlet.Adding a second obstacle, the rapid stream between two obstacles occurs strong turbulence phenomenon for the reason of being blocked, in the same time, also produced a wave to propagate upstream. Due to the flow speed is faster than the wave speed, wave unable to continue spread to the upstream and disappeared between the two obstacles, water depth increases and slop over the top of the second obstacle, relevant hydraulic state is similar to it when it is only an obstacle. After the flow became stable, the water depth of the first obstacle upstream increased further.The upstream water depth of the first obstacle increases with the increase of the slope and obstacle grade.Aiming at hydraulic condition in the course of the experiment, qualitative analysis was undertaken in theory. Focusing on the factors of water depth change, regarding pipe flow as weir flow processing, got fit relationship between flow and weir head in the station of different obstacles grades, based on which, from the engineering point of view, defined a kind of method to carry out quantitative analysis and obtained tables of the influence of different obstacle grades on pipe flow ability under different pipe slops and design fullness degrees, which is helpful for pipe design and maintenance and has important engineering significance.