Gravel

• Granite is generally recommended over limestone for all drainage applications. Granite is both more chemically stable, and more resistant to crushing over time.
• Granular material for underdrains should be clear crushed 20 or 50 mm diameter stone graded in accordance with ASTM D 2940.
• The 20 mm clear crushed aggregate permits the use of an overlaid layer of high performance bedding (HPB) as a choker layer.
• The void space ratio should be > 0.35 (or > 35%)

All gravel should meet the following criteria:

• Maximum wash loss of 0.5%
• Minimum durability index of 35
• Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions

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.

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.

The void ratio (e) of a mixture is the ratio of the volume of void-space to the volume of solids. It is closely related to the concept of porosity (n) where porosity is the ratio of the volume of void-space to the total or bulk volume of the mixture. e = Volume of voids/Volume of solids = n/(1-n)