Study On Anti-silt Design And Performance Of Double-layer Permeable Asphalt Pavement Based On Fractal Theory

Permeable asphalt roads play a super role in "infiltration" and "storage" in the face of rainwater.At present,it is mainly used in urban roads,squares and parking lots.However,the mixed flow formed by surface sediment and rainfall continuously enters the interior of the pores,gradually forming blockage,and the permeability function is continuously attenuated or even completely lost.The current domestic research and construction focus on how to achieve better water permeability,but ignore the research on the key technology of comprehensive prevention and control of sponge siltation.Previous studies have shown that no matter what cleaning technology can only effectively remove the blockage within 3mm of the surface,the pavement will continue to be blocked,with heavy workload and high cost,which limits the wide application of permeable asphalt pavement.Based on the project of Jilin Provincial Department of science and technology "Research on Key Technologies of Comprehensive Prevention and Control of Permeable Pavement Congestion in Sponge City Construction",this paper puts forward a double-layer permeable asphalt pavement with small particle size,small gap and large porosity.Based on the fractal grading theory,four anti-silting layers are designed and planned to be selected.The effect of each layer is evaluated through water permeability test,indoor siltation test and road performance test,and then the grading is optimized.The effective anti-silt layer with grade S（PAC5）and C（PAC5）and the bearing layer with grade F（OGFC16）are bonded according to different thickness ratios to verify the road performance,shear resistance and slip resistance of the designed double-layer permeable asphalt pavement.The effects of different gradation and double layer thickness ratio on water permeability,silt prevention and road performance were analyzed through laboratory tests.Finally,the discrete element method is used to establish the particle infiltration numerical model of permeable asphalt pavement under different gradation and the mixed flow siltation model of silt and water in permeable pavement through PFC3 D,and the preventional effect of proposed grade matching siltation is studied by simulating the siltation process.By this method,the spatial distribution of silting material and pore distribution characteristics of different gradation mixtures can be seen intuitively,and the anti-silting ability of planned gradation can be determined.The results show that the optimal gradation S can be used as an effective anti-silting layer to ensure the water permeability and road performance.The optimal combination mode of double-layer pervious asphalt pavement is that the gradation S with a thickness of 2cm is used as the anti-silt layer,and the gradation F with a thickness of 4.35 cm is used as the bearing layer.