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| For advice on decorative surface aggregates see [[Stone]]<br> | | <poem> |
| 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]] |
| | Gravel for underdrains and underground infiltration structures should be 20 - 50 mm, uniformly-graded, clean (maximum wash loss of 0.5%), 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>. |
| | The uniform grading and the angularity are important to maintain pore throats and clear voids between particles. (i.e. achieve the void ratio). |
| | The clean wash is to prevent rapid accumulation of fines in the base of the reservoir. |
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| Gravel with structural requirements should also meet the following criteria: | | Gravel with structural requirements should also meet the following criteria: |
| *Maximum wash loss of 0.5%
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| *Minimum durability index of 35 | | *Minimum durability index of 35 |
| *Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions | | *Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions |
| | </poem> |
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| [[category:materials]] | | [[category:materials]] |