Study On Seepage Characteristics Of Asphalt Pavement Structure

The early water damage of asphalt pavement is closely related to the permeability of asphalt mixture.The coefficient of AC-13 and AC-20 under different conditions was tested with the application of pavement material permeability testing system under the condition of multi-field coupling developed by our research group.The influence of different factors on the penetration performance was analysed,and the application scope of Darcy’s law in the case of asphalt pavement seepage was also surveyed.The seepage form of of each section and layer was acquired using the test device of seepage form of asphalt pavement structure developed by our research group.The major research results are as follows:(1)The influence of six factors on the permeability of asphalt mixture was studied such as temperature,porosity,maximum nominal particle size,forming method,axial pressure and hydraulic pressure.The study show that the void ratio has a greatest influence on the permeability of asphalt mixture.The greater the void ratio,the larger the permeability coefficient,which indirectly proves that 8%of the porosity is the turning point of the rapid increase of the permeability of asphalt pavement.The permeability coefficient of asphalt mixture increases with the increase of temperature,the maximum nominal particle size and axial pressure,and decreases with the increase of water pressure.Under same voidage,permeability coefficient of proctor compaction molding specimen is more than permeability coefficient of rotating compaction molding specimen.(2)The applicability of Darcy’s law in the seepage of asphalt mixture is discussed by using Forchheimer Non-Darcy percolation theory.The non-linear relationship between the flow velocity and the hydraulic gradient is fitted by the Forchheimer formula.Darcy seepage is considered that when the quadratic term(inertial force term)is much lesser than the first term(viscous resistance term)which determines the scope of Darcy’s law.The study show that the critical velocity value of the Darcy seepage of asphalt mixture AC-13 and AC-20 is suggested as 0.01 to 2.18×10-2cm/s and 0.07 to 2.67×10-2cm/s respectively,the critical hydraulic gradients value is suggested as 2 to 158 and 17 to 116 respectively,and the critical Reynolds number is 0.01 to 3.59 and 0.06 to 5.45 respectively for rotary compaction.The critical velocity value of the Darcy seepage of asphalt mixture AC-13 and AC-20 is suggested as 0.02 to 2.21×10-2cm/s and 0.16 to 3.81×10-2cm/s respectively,the critical hydraulic gradients value is suggested as 7 to 133 and 11 to 106 respectively,and the critical Reynolds number is 0.01 to 3.64 and 0.14 to 7.77 respectively for compaction.(3)The effects of loading times,horizons,thickness and gradation on the seepage area of asphalt pavement structures were compared and analyzed by using Image-pro plus software to extract percolation area parameters from the fluorescent agent tracer image of the seepage specimen.It’s showed that the area of seepage form of different layers of different sides of the same specimen present a similar trend of first increase and then decrease with the increase of loading times.As to the same specimen,in order of the seepage area of different layers,it goes:the upper layer,the lower layer and the middle layer.The thicker the asphalt pavement is,the bigger the seepage area is.The seepage area of the upper layer of SMA-13 is larger than that of AC-13,and the seepage area of the lower layer of ATB-25 is larger than that of AC-25.