Finishing grades and surface layer installation: permeable pavements

Bedding course being spread across the infiltration area. (Photo Source: CVC, 2012)

The bedding layer consists of a coarse stone and provides a level medium onto which paved surfaces are installed. Note that bedding layers are required for permeable pavers but not porous concrete. Additionally, the bedding layer can function as the choker layer, depending on the design.

Construction Steps:

1. Place stone bedding material on top of compacted reservoir course.
2. Level aggregate to the appropriate depth, as per the design. A vibratory screed can be used to level the bedding material.

Key Inspection Points:

• Granular bedding material is correct size and material (e.g. 5 mm stone) upon arrival to site. For an example of a municipal standard for gradation and material size, refer to (City of Toronto, 2021).
• Bedding depth conforms to design and is uniform across the LID feature.
• When a 3-metre straightedge is placed on the surface of the bedding material, gaps between the straightedge and bedding surface are not greater than 10 mm at any point.

Mistakes to Avoid:

• Fines in the aggregate – ensure that the correct stone gradation is provided and the medium is free of fines and crushed stone. See Jar test to ensure there are no fines in the crushed stone aggregate.
• Compaction – the bedding layer cannot be compacted
• Use of plate vibrators – do not use plate vibrators for levelling, as they can crush the bedding material. Tamping should be performed after the installation of the pavers.

For more guidance on materials specifications, refer to Aggregates, OPSS aggregates and (Ontario Provincial Standards, 2013)

---

Credit Valley Conservation

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Soil particles with a diameter less than 0.050 mm.

Soil particles with a diameter less than 0.050 mm.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.