Drainage Issues Related to Porous Pavements

The paper deals with the issue of the drainage of porous pavements. This kind of pavements can be divided into two main categories: full depth porous pavements and pavements in which only the friction course is porous. The first is widely used in parking lots and in urban areas where no heavy traffic is expected. For all other purposes, porous friction courses are used: 3 ÷ 5 cm thick in the European practice, about 2 cm in the US practice. The paper focuses drainage issues related to these porous friction courses. After a brief description of the main features adopted to solve this problem, a model is presented in order to predict the need of sub-drains and their spacing. This model is the evolution of a previous one, in which some corrections have been introduced taking into account some empirical findings. Originally the model was solved in order to find the maximum level of the water table flowing within the porous friction course. After the introduction of the empirical correction, the model has been further managed in order to find the maximum flow path length before the water starts flowing over the pavement. Thus, it has been solved again using the Runge-Kutta method and several runs have been performed simulating various scenarios of porous friction courses exposed to rainfall. The results of these simulations are reported in tables that provide the maximum flow path length that should not be exceeded to avoid the surface runoff. These tables can be useful for practitioners to correctly design drain spacing. For a given road section, the designer simply have to verify that the designed drain spacing does not exceed the maximum flow path length provided by the tables