Experimental Study On The Filtration Efficiency Enhancement Of Stormwater Runoff In Permeable Pavement By Geotextiles

Geosynthetics used in different types of green stormwater infrastructure（GSI）mainly play the role of filtration,isolation,protection,seepage prevention and drainage,so as to improve the capacity of infiltration,storage,purification,utilization,discharge and etc.of the facilities.The main functions,requirements,performance and applicable conditions of geosynthetics in different GSI are summarized in this paper.The parameter requirements and improvement effects of geosynthetics applied to typical GSI such as infiltration facilities and permeable pavement are emphatically analyzed.A large number of pollutants accumulated on urban roads and other underlying surfaces are washed by stormwater runoff into receiving water bodies,causing pollution threats.Permeable pavement is one of the effective measures to reduce runoff pollution.In order to study the effect of geotextiles on the total runoff control of permeable pavement facilities,artificial simulation of uniform rainfall was used to study the effects of different specifications of geotextiles on the concentration and particle size of suspended solids（SS）,total nitrogen（TN）,total phosphorus（TP）,ammonia nitrogen（NH₃-N）,COD,heavy metal and runoff volume control by adding geotextiles into permeable pavement.Suggestions on the prevention of clogging and maintenance of geotextiles,the selection of geosynthetics in GSI and the application direction of new materials are proposed.This paper studies the following contents and draws corresponding conclusions:（1）Geotextiles with different materials,specifications and layers have different control effects on various pollutants and effluent pollutants of different types of permeable pavement,which enhance the removal effect of pollutants to a certain extent.In terms of the removal effect of dissolved pollutants,the removal rate of COD,TP,TN and NH₃-N is higher with a double layer of 600 g/m² geotextiles of polyester filament and polypropylene staple fiber in permeable pavement.Pervious asphalt concrete pavement has the greatest effect on improving the removal rate of dissolved pollutants by adding geotextiles.After operation for a period of time,TP,NH₃-N,COD of permeable pavement effluent can still be improved,but TN removal effect is not good.（2）For heavy metals,geotextiles can effectively improve the removal rate of heavy metal ions（>90%）,and enhance the stability of effluent concentration.Double-layer,400～600 g/m² polypropylene staple fiber and polyester filament geotextiles are more suitable.Mn,Zn,Ni,Pb,Cd were best removed by polypropylene staple fiber geotextiles,and Cr were best removed by polyester filament geotextiles.The removal effect of Cu was very good for two kinds of geotextiles.（3）As for the removal effect of granular SS pollutants,The SS removal rate of pavement with double layer 200 g/m² geotextiles is 67.00%.On this basis,the removal rate can be increased by 2.4～3.3 per 100 g/m² geotextile of the same specification,and the maximum SS removal rate of pavement with double layer 600g/m² geotextiles reached 89.71%after 90 min of effluent.Geotextiles can effectively remove SS with0～76μm particle size which is difficult to be removed by permeable pavement devices.The removal effect of polyester filament geotextiles are better.In permeable cement concrete pavement,geotextiles play a role in relieving the blockage of structural layer through interception and isolation.The pore size of permeable cement concrete pavement is large,and the removal effect is enhanced greatly after adding geotextiles.（4）For runoff volume,double-layer,polyester filament geotextiles have the best permeability effect.Permeable pavement with specifications of the thinner geotextiles,the more water permeable.Within a certain range of the same material specifications increased by 1 times,geotextile drainage coefficient decreased by about 10%.Adding geotextiles can absorb water,alleviate the blockage of pavement structure.It is beneficial to better drainage of pervious pavement and ensure the stability of outlet water quantity.The water permeability of permeable asphalt concrete pavement with geotextiles is the most significant improvement.