The components of permeable
paving depend on the type of paving used, but are similar to those
of conventional paving. The system normally consists of a wearing
layer, a bedding layer, a base, and a sub-base over a sub-grade. A
system of unit pavers with aggregate in the voids between pavers provides
infiltration of water straight to the bedding layer and sub base.
Porous paving allows for water to flow through the pavement itself
into the bedding layer. These two systems can be combined. Grass paving
consists of an interlocking layer of plastic cells that provide structural
support for vehicular use, while containing planting mix that allows
the grass roots to grow.
Typical
Permeable Paving Components
In situations
where the existing sub-base cannot infiltrate the stormwater load,
a sub-surface drainage system may need to be installed.
Small pieces of stone, called fines,
can block the spaces between the aggregate and affect the water storage
capacity of the base layers. For this reason, no-fine aggregates are
placed between the pavers and in the bedding layer in permeable paving
systems. Geo-textile fabrics can be inserted between layers to keep
the fines from migrating through the layers.