Study On Saturated-Unsaturated Seepage Characteristics Of Subgrade And Pavement In Rainy Area

Water damage is one of the main types of highway subgrade and pavement distress in rainy area. Although there are numerous causes of subgrade and pavement’s water damage, in essence, it is closely related with the saturated-unsaturated seepage in subgrade and pavement. In rainy area, the rainfall is not only heavy but also long duration in rainy season, so studying the characteristics of subgrade and pavement saturated-unsaturated seepage is instructive for highway drainage design optimization and prolonging the service life of highway.This paper researched the characteristics of subgrade and pavement saturated-unsaturated seepage by the method of field test and numerical simulation on the basis of theoretical analysis. The main research work of this paper includes:(1) Starting from the saturated porous media seepage differential equations, derived the saturated–unsaturated seepage differential equations based on introduction of the basic concepts of unsaturated porous media, and briefly discussed the application of saturated-unsaturated seepage theory in the seepage of subgrade and pavement. The results show that the model material parameters and boundary conditions need to be treated with caution when solving the saturated-unsaturated seepage problem of subgrade and pavement.(2) Carried out the field seepage test of subgrade and pavement relying on the North Second Ring Expressway of Guangzhou actual project. Monitored the subgrade moisture for a long time by using TDR-3 moisture sensor. Test results show that in the heavy rainfall season, the larger water content position mainly is concentrated in the depth of 130cm~200cm; subgrade and pavement of saturated-unsaturated seepage is a slow process, and water infiltration process showed obvious temporal.(3) The numerical simulation method was used to study the characteristics of saturated-unsaturated seepage of subgrade and pavement in rainy area. The feasibility of the numerical analysis was verified by the measured date, and the effect of rainfall intensity and duration on the saturated-unsaturated seepage characteristics of subgrade and pavement is analyzed. Research results show that when the rainfall last for a long time, the pavement structure layers have continued saturation phenomenon, then with the rain stopped, moisture dissipation speed become slow; when the rainfall intensity exceeds a certain value, the effect of the roadbed’s water rate distribution by the rainfall intensity isn’t obvious.(4) The effect of pavement subsurface drainage system on the saturated-unsaturated was studied. The results show that the drainage base can effectively remove water in pavement structure; the drainage cushion can also reduce the size of internal saturated zone of subgrade and pavement; the effect of edge drainage system on the saturated-unsaturated seepage of asphalt pavements is not significant.