Experimental Study On Sediments Variation Characteristics Of The Lower Channel Of Double-layer Sewer

Drainage pipeline is an important urban infrastructure and has a vital impact on the investment costs, land use and operating maintenance of the urban drainage system. At present, interceptive combined sewer system and separated system are adopted internationally,but they are with pollution problems due to combined overflows(CSOs) or first flush, respectively. A new type 2in1 double layer drainage system has been proposed and developed by Chongqing University research team which the author worked in. This system has been proved to be with the function of first flush interception and CSOs prevention.Sediments are a common problem encountered by most urban drainage pipes, which not only can corrode pipes and reduce capacity of water delivery, but also cause urban water environment deterioration in wet weathers due to shock pollution loadings derived from sediments flushing. Therefore, in order to investigate the sedimentation characteristics of the lower channel of the 2in1 double-layer sewer both in dry weathers and wet weathers with first flush interception, and to further provide supports for operation, maintenance, management and application of the new sewer, experiments were carried out on migration characteristics of sediments in the lower pipeline of the new double-layer urban drainage pipes in this thesis. The main results are as follows:â‘  For the separately run of the lower pipeline, the distribution in the deposition length and the variation characteristics of deposition rate and particle size with pipeline model, flow rate and concentration of sewage are obtained. At the same time,the fitted equations about the distribution and variation are obtained.â‘¡ For the case of the through of trapping rainwater in the upper pipeline, the impact of trapping rainwater on the distribution and variation characteristic of deposition in the lower pipeline is studied. Centered on lower pipeline, the distribution in the deposition length and variation characteristic of deposition rate and particle size with sewage flow rate, the flow rate of combined sewage and interceptive rainwater concentration are obtained. At the same time,the fitted equations of particle size with the sewage flow rates, combined sewage flow rate and interceptive rainwater concentration are obtained.â‘¢ Based on the theory of hydraulics and the different pipe cross-sectional shapes, the formula of the main hydraulic parameters of two different pipe cross-sectional shapes in different deposits fullness with 0.5RH1 and 0.5RH4 are obtained. Based on which thechange of flow cross-section area, hydraulic radius, velocity and flow in different deposits fullness of the lower pipes is analyzed.â‘£ In the flush test,the change law of effluent concentration of SS and particle size in different double-layer pipe shapes, flow velocities of combined sewage, concentrations of rainwater intercepted and deposit rates with flush time is obtained. At the same time,the fitted equations of the change law are established when the effluent is steady, which can be used to direct the dredging of the pipeline deposit in the lower pipeline.