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| Gravel for underdrains and underground infiltration structures should be 20-50 mm, uniformly-graded, clean, crushed angular stone that has a void ratio of 0.4 (40%)<ref>Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017 </ref>. | | For advice on decorative surface aggregates see [[Stone]]<br> |
| | Gravel for underdrains and underground infiltration structures should be 20 - 50 mm, uniformly-graded, clean, crushed angular stone that has a void ratio of 0.4 (40%)<ref>Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017 </ref>. |
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| | Gravel with structural requirements should also 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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| [[category:materials]] | | [[category:materials]] |