| Permeable asphalt concrete pavement is one of low impact development(LID)practices that support both traffic function and stormwater control efficiency.It can effectively decrease the impervious surfaces in urban road areas,and thus reduce the risk of flooding under high rainfall conditions.However,the research on stormwater control of permeable pavement is still in the early stage,the relationship between the evaluation index in the process of rainfall infiltration and pavement structural design parameters is not clear,and thus the adjustment of design parameters,such as porosity,permeability coefficient and thickness,lacks of theoretical basis and necessary experimental support in the functional design stage.Based on the saturated-unsaturated seepage theory of porous media,it is analyzed in this paper that the unsaturated two-phase flow(water and gas)in permeable asphalt pavement system and the generation process of surface rainwater runoff under rainfall conditions.At first,On the basis of determining the structures of permeable asphalt pavement,the process of rainwater infiltration in permeable asphalt pavement system is simulated in a self-designed indoor experimental device.And it is studied that the effects of pavement structural design parameters,such as porosity and thickness of permeable pavement layers,on the seepage characteristics of pavement system.Then,a numerical model of permeable asphalt pavement system is established in finite element software,and the hydraulic parameters of the model are validated by the data measured in experiments indoors.Considering the influence of the coupling effect between groundwater and infiltration rainwater on the permeability of pavement system,the impacts of different types of subgrade soil and groundwater conditions on the overall permeability of pavement is analyzed in the model.Finally,based on the control target of stormwater runoff in road area,the regional hydrological model of an actual road engineering cases is built by using the Storm Water Management Model(SWMM).And the efficiency of permeable asphalt pavement on local rainwater control and treatment is analyzed and concluded from the macroscopic performance of storm water management.The main conclusions of this paper are as follows:(1)The permeability coefficient of the permeable asphalt concrete pavement has little effect on the overall permeability of the system.But the permeability coefficient of the base has significant influence during and after rainfall events.The thickness of graded macadam subbase is the main factor affecting the storage capacity of permeable pavement.and the contribution of the thickness of surface and base to the water storage of pavement system is very limited.The moisture holding capacity of subgrade soil is a dominating factor that cause the difference of water retention performance in several designed pavement systems.(2)The impact of groundwater level on the seepage rate in permeable pavement layer is not obvious when the burial depth of groundwater level is large enough.However,when depth is small,groundwater can enter the pavement structure layer through capillary action,cause the fluctuation of seepage rate at the initial stage of rainfall and reducing infiltration rate at the stable seepage stage.(3)From the point of view of stormwater runoff control,permeable asphalt pavement,as a LID practice,has shown good efficiency in three aspects: total annual runoff control,water ponding control in road area and hydraulic load reduction of rainwater pipeline network. |
PDF Full Text Request