Gravel

• Granular material for underdrains should be clear crushed 50 mm diameter stone graded in accordance with ASTM D 2940.
• 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

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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.

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)