The Mechanics of Porous Paving: How It All Works

The grass- or gravel-filled porous pavers are the first level the system

The process of water infiltration begins with the surface layer. Porous paving solutions like Grasspave2 or Gravelpave2 have 92 percent void spaces, which is about three times that of alternative permeable paver options like concrete paver blocks as well as porous asphalt and concrete. A larger volume of void space directly translates to a better drainage capacity, which is further enhanced with the fill material, be it grass or gravel.

In application, porous pavers hold the fill material, which filters the stormwater, allowing it to pass through the spaces between them and into the ground below. Because the proportion of void spaces influences performance, alternative permeable paving options (8-20 percent void space) drain at about 6.4 inches per square foot per hour. Whereas Grasspave2, which is a porous pavement filled with grass, drains 32.5 inches of water per square foot per hour and Gravelpave2, a porous paver filled with gravel, has a drainage rate of 38.5 inches per square foot per hour. 

A strong and stable base course is crucial to a porous paving system

Once the water passes through the fill material and flexible porous paver, it continues to flow downward and reaches the base course. A base course is a layer of gravel or aggregate installed between the subgrade (the natural ground) and the surface layer of a pavement structure. Serving dual roles of a foundation and a reservoir, the base layer helps infiltrate water into the water table or water detention system while also evenly distributing the load of the activities on the surface. In doing so, it prevents pavers from shifting or settling over time.

Because the base course will influence the stability and longevity of a porous paving system, its depth recommendation will vary by use— from a very shallow 2-inches for pedestrian and light stormwater capture, to 12-inches deep for heavy stormwater drainage.  

Selecting the best materials for porous paving system based on site- and project- specific requirements

Because the base course is essentially the backbone of the pavement structure, choosing the right  materials underneath a porous paver is important for its stability and performance. Factors like local climate and soil conditions significantly influence this choice, as they affect freeze-thaw cycles, soil types and water table levels. Additionally, project-specific requirements, such as anticipated traffic loads and aesthetic preferences, will also play a role in the decision-making.

Commonly used base course material includes sandy gravel and crush stone aggregate. Their well-graded particle size allows excellent drainage and load-bearing capacity, making both popular options. Similarly, open-graded aggregate is particularly favored beneath porous paving in high-flow areas, owing to its ability to promote rapid water infiltration.