Study On Hydraulic Calculation And Characteristics Of The Lower Channel Of A Novel Double-layer Sewer

Urban drainage system is an important kind of urban infrastructure. As one mainbasic component, it is of great impacts on the investment, land use and operation andmaintenance of the total urban drainage system. It is well known that currently widelyapplied combined sewerage system and separate sewerage system are with the problemsof overflows and first flush runoff pollution and misconnection, while the alternativesstill in developing such as stormwater retention tank are infeasible to most of thedeveloping countries due to high cost, extra land use and other issues. So it is necessaryto develop new drainage systems which have the function of first flush runoffinterception by itself.An in-line first flush runoff interception system based on novel double-layer pipeand double-layer manhole has been developed, which is able to achieve theabovementioned function. However, as an interlayer with various shapes is set, thelower channel of the double-layer pipe will have special hydraulic characteristics whichwill lead to different hydraulic calculation method. This dissertation is intended to carryout researches on this topic by using theoretical analysis and experiments. The keyresults are as follows:(1) Hydraulic calculation for the lower channel of the double-layer pipe wasstudied theoretically with application of fundamental hydraulics and with respect to theparticular section shape, and the influencing effects of change of the interlayer both inshape and position (height) on.the hydraulic parameters both for the upper channel andthe lower channel were analyzed, and some basic important findings were obtained. thecalculation formula of common hydraulic elements of cross section was summarized,with respect to the geometrical characteristics of cross section, and general calculationformula for hydraulic elements and the critical water depth of the0.50R series standardegg shaped double drainage pipeline were deducted, in which0.5RH1lower layerpipeline non-full flow in a degree of0.1and0.5is divided into three section,0.5RH2type pipe lower pipe of non-full flow in the full degree of0.1651and0.8256is dividedinto three parts,0.5RH3type pipe and lower pipe non-full flow in a degree of0.1339and0.8368is divided into three parts,0.5RH4type pipe and lower pipe non-full flow ina degree of0.1136and0.8523is divided into three parts, hydraulic calculation formulasof parameters in different fullness degree obtained according to the geometric characteristics of the solution; the0.50R series of egg-shaped double-layer drainagepipeline were analyzed, the lower and upper pipeline is full flow area ratio in0.37～0.92,0.75~1.27weeks than in the wet, flow ratio of0.23to0.80, the velocity ratio in0.51~0.88, two of the ratio of the maximum velocity in0.76～1.05,0.29～1.1betweenthe maximum flow ratio. Barrier height variation of hydraulic parameters of the pipelinehas remarkable effect, interlayer radian change has little effect on the hydraulicparameters.0.50RH4shape tube double drain pipe and lower pipe section area in fullflow, double pipe lower pipe flow and velocity is0.878times of circular pipe, themaximum flow rate and flow velocity of double pipe layer pipe are respectively1.02times and1.043times of the circular pipe, and the height and width of circular pipe arerelatively small, comprehensive arrangement is more advantageous to the undergroundpipeline;(2) Through calculation and analysis of0.50R series of egg-shaped hydraulicparameters of double-layer drainage pipeline lower pipeline, changes of related mainhydraulic parameters, namely the wetted perimeter with a single increases fullness, andflow velocity, hydraulic radius is at the starting stage with increasing fullness degreeincreases, but when the depth of top arc contact, it will decrease with increasing fullness;interlayer radian is the same but the location is not at the same time, variation ofhydraulic parameters are consistent, hydraulic radius, velocity and flow rate willincrease with the increase of barrier height.(3) Based on the analysis of the hydraulic experimental double pipe lower fluid, togain an understanding of the empirical hydraulic characteristics of fluid in pipeline. Theresults show that: with the increase of pipe flow with the present single increased,reached the maximum at full flow; for egg shape double drainage layer, velocitycalculation formula is Chezy formula should be corrected coefficient C value accordingto the structure characteristics of the pipeline itself.