Numerical Modelling Study of Subsurface Drainage of Permeable Friction Course Considering Road Geometric Designs

This study aimed to evaluate the subsurface drainage of a permeable friction course (PFC) via two-dimensional finite element analysis. To achieve the scope, PFCs with equivalent water flow paths of length values of 10, 15, 20, and 30 m and slope values of 0.5%, 2%, 4%, 6%, and 8% were modelled based on FEniCS and implemented entirely in Python programing language to extract the time for surface ponding according to a range of rainfall intensities. The results show that when the rainfall intensity and the length of equivalent water flow path of the PFC rose, the time for surface ponding decreased. For instance, with a rainfall intensity of 10 mm/h and a slope of 0.5%, when the length of equivalent water flow path increased by 20 m, the time for surface ponding dropped by 21 min. Moreover, when the slope of the equivalent water flow path and the thickness of the PFC increased, the time for surface ponding increased. For instance, with a rainfall intensity of 10 mm/h, and a PFC with an equivalent length of 10 m, when the slope increased by 16 times, the time for surface ponding increased more than two times. The current study highlights that the thickness of the PFC has the most influence on subsurface drainage. The findings of this study indicate that at high rainfall intensities, the subsurface drainage of a PFC is not sensitive to its geometric design. Further experimental investigations are needed to evaluate and validate the subsurface drainage of a PFC considering permeability, rutting, and environmental factors.