Finishing grades and surface layer installation: permeable pavements

Bedding layer

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)

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Placement and installation

Placement and Installation

Paver installation

Permeable pavers have the highest load tolerance of the permeable pavement variations. It is especially important that the permeable pavers be installed correctly on the bedding material. See Permeable pavements: Specifications for more information.

Construction Steps:

1. Lay permeable pavers by hand or install whole pallets of pavers at a time with specialized equipment.
2. Cut pavers to fit into the edges of the infiltration area.
3. Fill voids between pavers with joint aggregate.
4. Sweep excess joint aggregate from pavement surface.
5. Compact completed surfaces with a plate vibrator at the end of each day or when all pavers are placed. The plate vibrator can be applied up to 1.8 m from the laying face (incomplete edge).

Key Inspection Points:

• Cracked/broken pavers are discarded and replaced with intact pavers prior to filling void spaces.
• Sizes of pavers and joint width conform to applicable municipal standards.
• Pavers conform to the specifications of the design.
• Minimum setback of 1.8 m from the laying face is considered when compacting at the end of each workday.
• Cut pavers are installed to edges of the practice before compaction of completed sections takes place.
• Pavers are elevated within 3 mm to 10 mm above adjacent inlets or channels.
• Paver pattern and joint widths conform to the directions of the manufacturer.
• Permeable pavers are compacted at least twice with a plate compactor.

Mistakes to Avoid:

• Leaving pavers uncompacted – finished surfaces must be compacted at the end of each workday.
• Cutting blocks in infiltration area – edge pavers should be cut with a wet saw in a designated area away from the infiltration area to avoid clogging with fines and dust.

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  Installing entire pallets of pavers is possible with specialized equipment. (Photo Source: CVC, 2012)

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  The equipment shown can install single pallets of pavers all at once. (Photo Source: TRCA, n.d.)

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  Joined permeable pavers being installed with a crane. (Photo Source: TRCA, n.d.)

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  Pavers cut to the shape of the adjacent curb at IMAX Headquarters in Mississauga. (Photo Source: CVC, 2013)

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  Finished parking lot at IMAX Headquarters in Mississauga. (Photo Source: CVC, 2013)

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  Cutting pavers within the infiltration area is not advised as the fines/dust could clog the permeable surface. (Photo Source: CVC, 2014)

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.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

Toronto and Region Conservation Authority

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.