Study On Seepage Behavior Of Large-Scale Drainage Asphalt Pavement Based On Macroscopic Rainfall Test

With the rapid development of China ’s road traffic volume,some of the congestion is becoming more and more serious,and the reconstruction and expansion of trunk roads has become an urgent need.However,the reconstruction and expansion roads mostly adopt superwide cross-sections dominated by two-way eight-lane and two-way ten-lane,which greatly increases the drainage path of the road surface and brings severe challenges to road drainage.In order to eliminate the potential safety hazards caused by insufficient drainage capacity of ultra-wide cross-section roads,a single-layer drainage pavement structure is adopted at this stage.However,the seepage test stipulated in China ’s specifications only reflects the influence of material voids on seepage,and the pavement drainage is affected by many factors such as pavement slope,width,thickness and rainfall intensity,which makes it difficult to effectively control the pavement performance of the drainage asphalt pavement and hinders the promotion and application of the drainage pavement.In order to explore the real seepage situation of drainage asphalt pavement under rainfall environment,this study used a self-designed seepage experimental device to analyze the changes of water level and surface runoff depth inside the pavement during rainfall through laboratory tests,and to explore the temporal and spatial distribution of precipitation in pavement confluence.By using CT and image processing technology,the geometric characteristics of the void space of the porous asphalt mixture are obtained,the internal seepage field model of the mixture is established,and the internal seepage law of the mixture is obtained through simulation analysis.Based on the above experimental data and material parameters,the distribution of void water pressure and streamline in the special section of the trunk road is obtained by finite element numerical simulation,which provides a reference for the design of the drainage pavement structure of the super wide section trunk road.The results of this study are as follows:(1)Based on the self-designed rainfall test device,the pavement seepage of single-layer drainage asphalt pavement(width of 3m,thickness of 5cm)under short-duration(30min)rainstorm with different return periods was obtained,and the temporal and spatial distribution of pavement water level height and runoff change was statistically analyzed.It is found that under the action of rainfall,the internal water line of the pavement presents an arch-like distribution with high middle and low sides.The single-layer drainage asphalt pavement has insufficient drainage capacity in the case of short-term rainstorm,and there will be serious water accumulation.The maximum water depth in the test can reach 14 mm.The double-layer drainage asphalt pavement(width of 3m,thickness of 10cm)has good drainage performance in the case of short-duration rainstorm.The change of synthetic slope of pavement is the main factor affecting the drainage performance of pavement.When the slope is less than 1.5 %,the runoff of pavement will increase significantly.The strategy of setting drainage channels along the longitudinal slope to alleviate the runoff of the road surface is proposed.When the width of the drainage channel is 10 cm,the spacing should be less than 2.5 m.(2)Based on CT scanning and digital image processing technology,the spatial distribution and geometric characteristics of voids are studied.The results show that the connected void ratio directly affects the drainage performance of the mixture,and the geometric properties of the connected void(such as equivalent diameter,curvature,etc.)are important factors affecting the seepage velocity and seepage flow.(3)Based on the seepage theory of porous media materials,based on the macroscopic and microscopic test parameters,the rainfall infiltration finite element numerical simulation of the two-way eight-lane drainage asphalt pavement is carried out,and the rainfall infiltration numerical simulation is carried out on the vertical curve depression section and the super-high transition section with complex pavement alignment and easy water accumulation.The maximum depth of runoff and the range of water accumulation are obtained,which provides a reference for the drainage design of special road sections.