Study On Performance And Mechanisms Of Stormwater Infiltration And Water Purification Of Permeable Pavement Layers

As one of the major structural measures of Low Impact Development (LID),permeable pavement consists of permeable paving surface, bedding layer, permeablebasecourse and compacted subgrade. Permeable pavement has strong surfacepermeability and water purification ability. The studies before mainly concerned theinfluence of surface clogging on stormwater infiltration while ignoring the influencecaused by particle mass strained in the internal structure of each layer of permeablepavement (referred to as internal clogging in this paper). As to water purification, thepublished studies focused mainly on the qualitative impacts of various influencingfactors on the event mean concentration (EMC) of pollutants. Pollutants removalmechanisms inside each layer are rarely reported, let alone the water purificationmathematical models.In this paper, a small-scale permeable pavement was built and the stormwaterinfiltration rates and pollutant removal rates of each layer were determined throughthe indoor simulated rainfall to study the performance of stormwater infiltration andpollutant removal of each layer. The influence mechanism of internal clogging onstormwater infiltration rate and the purification mechanism of pollutant for each layerwere studied. The most effective thicknesses of sands and gravels were determined bycomparing the pollutant average removal rates and steady infiltration rates of layers indifferent thicknesses. Binary polynomial fitting method was used to establish amathematical model to represent the mathematical relationship of pollutant removalrate, the rainfall duration and thickness of layer, and meanwhile error analysiscombining with3D surface plots was carried out to test the model. Besides, a methodto deduce the water purification mathematical model for the whole permeablepavement was put forward. The results show that:(1) Internal clogging is the main factor for infiltration rate changes of permeableconcrete blocks and graded gravels. While the amount of internal clogging, the formof water and air resistance are the key factors to determine the steady infiltration rateof sands.(2) Three layers are all effective in reducing SS and TP while the removal ofnitrogen compounds is ineffective. In addition, the removal of COD is not perfect for both permeable concrete blocks and graded gravels. COD is removed mainly rely onsands.(3) SS and COD are removed mainly benefiting from precipitation and adsorptionfor each layer. TP is adsorbed to particulate matters to be removed in the form of SS.High intensity rainfall has less effect on the already intercepted SS while COD and TPare vulnerable to heavy rainfall.(4) The most effective thicknesses of sands and gravels are5cm and20cmrespectively. And the early30min of rainfall is an important time for pollutantremoval of each layer. Reasonable measures could be taken to improve the targetpollutant removal at this stage.(5) Binary polynomial fitting method can be used to represent the waterpurification mathematical model for coarse sand bedding layer and single-gradedgravel layer in the absence of previous research. And a method based on multi-stagedust removal theory is put forward to deduce the water purification mathematicalmodel for the whole permeable pavement.