Experimental Study Of Runoff Mechanism About Permeable Pavement-bioretention Combined System

With the rapid development of urbanization,impervious area has increased dramatically,which make rainwater problem aggravatingly,such as waterlogging disasters and runoff pollution.As one of the main surface of waterlogging and runoff pollution,urban road is an important research object in the field of stormwater management.Under the severe background of road waterlogging,the traditional treatment scheme,such as increasing rainwater pipeline design return period,building construction of end rainwater storage facilities could not solve the problem effectively.It should be considered that changing to end control from source control.The research shows that penetration pavement could reduce the urban road surface runoff effectively,and biological retention settings could cut the peak runoff and total runoff volume.If they are used in combination,it can solve the problem of the roads waterlogging,and saving the infiltration of rainwater,which may contribute to restoring urban hydrologic cycle.At present,the research work that aim at infiltration mechanism and hydrological control effect has been a lot,but the emphasis just focused on a single measures of runoff analysis,the runoff study that combined two as a whole is not enough.So the paper focus on the runoff mechanism of permeable pavement-bioretention combined system with rainfall intensity,road slope and overflow height as variable conditions,and carry out the research as following:(1)According to the existing research data,it analyzes the surface runoff mechanism of the permeable asphalt and seepage drainage mechanism.On the basis of soil water dynamics,it analyzes seepage process in analogical pattern,which may provide a theoretical basis for further research.(2)the research simulated runoff confluence process with different situations in 1 hour by controlling rainfall conditions and changing road materials under special slope(longitudinal slope 5%;cross slope 2%),monitored and analyzed the flow.The result shows: when rainfall recurrence period changes from 1a-20 a,the reduction rate of permeable road runoff could be 90%-57%;the total reduction rate of road peak runoff could be 91%-46%,that testify obvious peak reduction effect.The runoff coefficient of permeable asphalt could be 0.07-0.29;and 0.07-0.19 after combining with bio-retention.The rainwater collecting ratio of permeable asphalt gutter inlet could be 6%-13%,and bio-retention could reduce the total inlet flow by 95%-82%.(3)It makes some study of relation between runoff coefficient of permeable pavement and time/rainfall intensity.Runoff reduction of permeable pavement play a role when rainfall begins and ends,and reduction effect is weak at peak of the runoff.It found a runoff coefficient change by duration of rainfall intensity much more than rainfall intensity itself.If rainfall return period and total length increases,the function peak treads,and runoff coefficient distribution changes correspondingly(4)Internal vertical seepage and horizontal seepage of road surface are analyzed.It found that there is an interval when the surface seepage response to rainfall intensity rainfall.The surface runoff,horizontal/vertical seepage and water inflow ratio have been compared.When return period and composite slope increases,the flow rate ratio present different change trend.Under the small return period(P =1a),the ratio is different when compared to the rest of the return period.(5)It researches runoff reduction effect and seepage theory of bio-retention under different rainfall intensity and overflow height conditions.The peak runoff flow time could be delayed 345s-598 s by bio-retention when return period less than 10 years.The reduction rate of total runoff and peak flow could be 41%-100% and 38%-100% under different return periods.Rising overflow height affects total runoff reduction more apparently,and has large influence on seepage process.There is a certain functional relation between seepage flow and surface water height of bio-retention,which accords to Darcy's law(6)This paper briefly introduces the design points of the permeable pavement drainage system,and improves drainage system design with the characteristics of the coupled system.In addition,combined with the experimental phenomena,it optimized the design details of drainage ditches,water mouth and water cross ditches.The study based on the seepage theory,through the contrast experiment,compared hydrological control effect of the ordinary roads,permeable pavement and biological retention.By analyzing the inherent correlation of experimental data,it illustrates the law of runoff of permeable pavement through the characteristics of runoff coefficient.And through theoretical calculation,this paper derived the runoff and seepage formulas under different rainfall characteristics of bio-retention.Finally combining with the experimental phenomena,it puts forward some suggestions of the system with drainage design.The above research contents can provide certain reference for low impact development and construction in our country.