Multi-scale Study On The Seepage Behavior Of Porous Asphalt Pavement Considering Clogging Effect

Permanent seepage and drainage capacity is the key parameter to measure the performance of porous asphalt pavement,which is mainly controlled by the spatial distribution characteristics of internal voids in porous asphalt mixture.However,due to the compaction effect of aggregate particles caused by repeated driving loads,the accumulation of small solid particles in the voids of mixtures,causes the voids of mixtures are easily clogged,which leads to deterioration of water seepage and drainage capacity.In order to ensure the durable seepage and drainage capacity of porous asphalt pavement,it is necessary to study the seepage law in porous asphalt mixture and evaluate the main influencing factors of the attenuation of seepage capacity.Taking the seepage process in asphalts mixture for example,the combination of macroscopic and microscopic analysis were used to show the anisotropy of the water seepage process in porous asphalt mixture,and the decline of water seepage process in the porous asphalt pavement was quantified under the influence of clogging by multi-scale analysis.Macroscopically,the pore clogging of asphalt mixture is characterized by void controlling.The retained water inside the specimen and the penetration water was measured through the device for the lateral permeability of the asphalt mixture,so that the anisotropy of the seepage process of porous asphalt pavement under the influence of clogging conditions is quantified.Mesoscopically,the internal microscopic structure of the porous asphalt mixture was obtained based on X-ray CT scanning and digital image processing technology.The void ratio,the connected void ratio,the void equivalent diameter,the curvature and the minimum cross-sectional area were selected as the microscopic parameters to characterize the variation process of the void under the influence of the clogging condition.Combining macroscopic and microscopic analysis conclusions,a finite element model of asphalt pavement considering the effect of water-loading was established basing on the theory of seepage in porous media,the seepage process influenced by wheel load was simulated,pavement permeability coefficient was modified reasonably according to the microscopic analysis.Results show that the water seepage process inside the porous asphalt mixture shows obvious anisotropy,and the semi-connected void inside the mixture can be reflected by the retained water volume.Compared to the void ratio,the connected void ratio is moreaccurately to qualify the drainage performance.The drainage time is determined by the curvature of the void,drainage capacity is determined by the minimum cross-sectional dimension.Lateral seepage is significantly greater than vertical seepage,and the lateral seepage is 1.66~2.43 times that of the vertical seepage on average.With the void declining by clogging,both the vertical and lateral seepage are decreasing,and the vertical permeability decreases relatively faster.The wheel load can accelerate the vertical penetration inside the pavement.When the pores are severely blocked,the water diffuses in the lateral direction at the bottom of layer,and extends the residence time of water inside the pavement,which is unfavorable to the stability of pavement structure.In summary,high vertical penetration ability can quickly eliminate surface water and improve driving safety;when the pores are clogged and the void ratio is reduced,high lateral permeability is required to drain water from the pavement structure and improve the durability of the pavement structure.The water seepage process inside the porous asphalt pavement can be quantified by the analysis on the water seepage behavior of the porous asphalt pavement by the influence of the void clogging condition,and this research put forward the scientific guidance for the design and maintenance for the porous asphalt pavement.