Study On Infiltration-Excess Flow Behavior Of Asphalt Pavement In Consideration Of Macro And Micro Characteristics

Rapid and effective road drainage design is vital to ensure driving safety and improve road service on rainy days.When the rainfall intensity exceeds the drainage capacity of asphalt pavement,Infiltration-excess flow(IEF)will exist on the pavement surface or inside the surface layer.IEF includes the confluence process on pavement and the seepage process inside the surface layer.The waterlogging caused by confluence affects the driving safety,the seepage reduces the bearing capacity and durability of the road structure due to the erosion of the pavement materials.To explore the influence of IEF behavior on driving safety and drainage design,field observation test,and physical experiment are implemented based on the theory of hydrodynamics,seepage mechanics,and elastic mechanics.The combination includes finite element models and theoretical calculation analysis are considered,and micro digital image technology and numerical model with the dynamic grid are applied,The IEF behavior of dense graded asphalt concrete pavement and porous drainage asphalt pavement under natural rainfall is studied in macro and micro scales.First of all,the hydrodynamic pavement confluence model is proposed based on the twodimensional shallow water equation,and the above model has been verified by the depth and velocity measurement on the field.The influence of pavement geometric alignment on pavement confluence is analyzed at the macro scale.Meanwhile,the local flow field model is established at the micro-scale,and the variation of the runoff depth in the carriageway is analyzed.Secondly,on the premise of basic road performance,the porous asphalt mixture drainage test with different void ratio is carried out.By using the self-designed device,the seepage law of porous asphalt mixture is obtained,the micro characteristics of porous asphalt mixture are identified by image processing technology.The finite element model is established macroscopically to analyze the distribution of pore water pressure under the condition of void decline.Finally,according to the results at macro and micro scales,considering the difference between the critical runoff depth and the water depth of the wheel trace,driving safety is evaluated according to the macro flow field and the pressure distribution in front of the tire.The runoff depth and drainage time of porous drainage asphalt pavement are calculated.Refer to the pavement project,corresponding drainage optimization measures and maintenance measures are put forward.The results show that:1)The depth and velocity are the most important indexes to depict the IEF of asphalt pavement.For dense asphalt concrete pavement,pavement geometric alignment is one of the significant factors which affect the IEF on the pavement.The variation of pavement runoff depth with road width and rainfall intensity can be quantified by a power function.The influence of cross slope is more significant than that of the longitudinal gradient.In the transition section,the spatial distribution of runoff depth is affected by the linear change,and the maximum depth area appears at the downstream of zero cross slope(ZCS)and the inner location of the road.Moreover,the waterlogging range is significantly affected by the pavement width.2)For porous asphalt pavement,drainage capacity is determined by the voids' spatial characteristics.Macroscopically,the internal connection porosity is the primary factor affecting the drainage capacity.In this paper,it is proposed that the macroscopical connectivity of voids can be evaluated by the retention of water.The spatial anisotropy of the seepage in the mixture is related to the height.The increase of height makes the horizontal lateral seepage more obvious than that on vertical.At the micro-scale,the equivalent diameter and curvature of the connected voids are the important factors that affect the drainage volume and time.The filling degree of the seepage in the voids is affected by the pore water pressure and is closely related to the road traffic load.3)For driving safety,on the basis of obtaining the flow field,the runoff depth difference between wheel traces in the lane should be considered to evaluate driving safety in rainy days besides the critical sliding runoff depth.Meanwhile,the dynamic water pressure of the tread with different speeds also should be considered.When the voids of the porous asphalt pavement gap are blocked,waterlogging still may exist on the pavement.In this paper,the mathematical formula is used to quantify the ultimate rainfall intensity and the drainage index when the surface of the porous asphalt pavement became saturated.4)Keeping unhindered drainage is important for preventing the stability and durability of asphalt pavement declining.In the case of traditional centralized drainage of dense graded asphalt pavement,the increase of longitudinal gradient value and the blocking effect of curb lead to the increment of runoff velocity.The dense outfalls can not achieve the expected results when there exists a larger longitudinal gradient.In this paper,according to the pavement widening caused by reconstruction and expansion,the side strip drainage can be used.Referring to the drainage design requirements,water depth on surface and internal should be quantified and the drainage design method should be determined,such as the reasonable maintenance time.