| In recent years,the frequent occurrence of urban waterlogging has resulted in huge economic losses and casualties.However,the design return period standard of the existing drainage network in China is generally low,which is not enough to cope with the high return period storm flow.Based on the experience of foreign developed countries,Chinese scholars propose to build road major drainage system as the surface drainage channel to solve the problem of urban waterlogging.As the key node of the secondary distribution of the discharge load of the surface drainage channel,the accurate calculation of the discharge distribution of the road intersection is very important for the risk assessment of the downstream road discharge.At present,at home and abroad,the flow distribution calculation of road intersections is usually based on results of rectangular open channel with a flat bottom,ignoring the impact of the actual structure such as cross slope and turning radius on the flow field of intersections;At the same time,the highly simplified 0-dimensional or 1-dimensional Road intersection model is used for the flow distribution calculation in the mainstream cities in the world.The simulation error of the calculation accuracy of the model is large.In view of these limitations,hydraulic experiments of a T-intersection considering detailed structure such as cross slope and turning radius were carried out.It is studied that the influence of hydraulic parameters and road slope conditions on the flow distribution at intersections.Based on the result of physical test,the calculation accuracy and efficiency of one-dimensional and twodimensional mathematical models of the road intersection were compared and studied.The design method of the major drainage system of the road is established,which is coupled with road intersection flow distribution calculation and SWMM mode.Finally,it is applied to practical engineering case.The research results make up for the existing physical experimental device neglecting the detailed structure problems such as road cross slope,improve the calculation accuracy of SWMM intersection flow distribution,and provide technical support and theoretical basis for the design of road as discharge channel in China.The research contents and main conclusions are as follows:(1)Influence of design parameters and hydraulic boundary conditions on the flow distribution at road intersectionsInfluenced by the fluctuant terrain characteristics of the roads in mountainous cities,the transition of the flow pattern between the rapid flow and the slow flow occurs frequently in the process of road drainage,results in the variation of the downstream hydraulic boundary conditions.The steep slope torrent often makes the downstream road flow freely.And when the road gradient changes from steep to slow,the downstream road may form backwater jacking.Hydraulic experiments of T road intersection were carried out,to study flow distribution of the intersection under free outflow and backwater jacking of downstream,then to reveal the influence of road slope,inflow and other parameters on the flow distribution of downstream road under different boundary conditions.1)Under the condition of free outflow,the flow distribution of intersection is mainly affected by the slope and hydraulic conditions of upstream road and intersection;With the increase of the longitudinal slope of the main road of intersection,the flow distribution ratio(which is radio of branch flow to upstream flow)changes with the increase of the inflow of upstream Road,from the decrease and rapid decline to the slow decline,to the gentle descending speed,and finally to the increase with the increase of the inflow flow of the upstream road;2)When the main road downstream is supported by backwater,the flow distribution ratio decreases with the increase of Froude number at the main road downstream;when the downstream roads are all backed up,the Froude number of the branch road and the downstream of the main road have the same relationship with the flow distribution ratio,which shows that the flow distribution ratio fluctuates in a small range with the increase of Froude number at the main road downstream;3)Under the condition of free outflow,the streamline at the turning of curbstone downstream of the intersection turns sharply,forming a hydraulic jump,which causes the local water depth to be too high,and easy to become the most dangerous area for discharge at the intersection;Under the condition of the main road backwater downstream,influenced by the water level jacking of the main road downstream,hydraulic jump in the intersection is formed.And at the same height of weir,the hydraulic jump position moves to the downstream with the inflow of the upstream road increases;4)Comparing with the existing studies,it was found that the flow distribution at the intersection with a free outflow downstream boundary condition is greatly affected by the cross slope and other detailed structures.This shows that the value of flow distribution ratio is larger than that of the existing experiments.While with the backwater effect from downstream,the flow distribution characteristics are quite different.This means the side slope of the roadway should be considered in the flow distribution computation.(2)Development of one-dimensional flow distribution model for road intersectionsIn view of the limitation that the existing one-dimensional model does not consider the influence of cross slope and turning radius on the flow field of intersection,based on the results of hydraulic experiment,the multi-dimensional linear regression and ridge regression analysis are used to identify the flow field characteristics of intersection under different boundary conditions and design parameters.And a mathematical model of flow distribution at one-dimensional intersection is constructed to explore the change rule of dimensionless parameters on the influence of boundary conditions.The results show that:compared with the existing one-dimensional model,the one-dimensional model considering the actual structure of the road cross slope can better reflect the flow distribution characteristics of the actual road drainage under the condition of free outflow.(3)Development of two-dimensional computational hydraulic model for Road intersectionAiming at the problem that the fitting effect of one-dimensional model is not good under the complex intersection type and extreme hydraulic conditions,and considering the two-dimensional flow characteristics of the intersection flow field,a two-dimensional hydrodynamic model of the intersection is constructed to improve the simulation accuracy of the intersection flow distribution model.According to the flow law and hydraulic knowledge of the physical experiment intersection,though extending the calculation area of the downstream road,a method is proposed to determine the calculation area and boundary conditions of the downstream of the two-dimensional model road by using the outflow curve and Manning formula.So it is used to improve the calculation efficiency under the premise of ensuring the accuracy.The simulation results of two-dimensional model show that the accuracy of flow distribution is high under the conditions of downstream free outflow and backwater jacking.Compared with the onedimensional model,the simulation results show that it can effectively make up for the lack of accuracy of the one-dimensional model in complex situations such as free flow on steep slopes.(4)Practical engineering applicationBased on the characteristics of high efficiency and low precision of one-dimensional model and high precision and low efficiency of two-dimensional model,the optimal modeling method of flow distribution calculation under different flow conditions is proposed.And a method of road drainage design which couples with road intersection flow distribution calculation with SWMM model was proposed.Taking a mountainous region in Chongqing as a case,the engineering application value of this study is investigated.Based on the model and method of this study,a major drainage system of the road in the study area is coupled hydraulically with the drainage pipe networks.The drainage capacity of the existing road drainage channel is evaluated.The retrofitting scheme is proposed to meet the requirement of the waterlogging control standard without changing the drainage networks. |
