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| − | All aggregates should meet the following criteria: | + | <ul> | 
| − | *Maximum wash loss of 0.5%,
 | + | <li>Granular material for underdrains should be clear crushed 50 mm diameter stone graded in accordance with [https://www.astm.org/Standards/D2940.htm| ASTM D 2940].</li> | 
| − | *Minimum durability index of 35,
 | + | <li>The void space ratio should be > 0.35 (or > 35%)</li> | 
| − | *Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions.
 | + | </ul> | 
| − |   | + | All gravel should meet the following criteria: | 
| − | *Granular material for underdrains should be clear crushed 50 mm diameter stone graded in accordance with ASTM D 2940.
 | + | <ul> | 
| − | *The void space ratio should be 0.4 (or 40%)
 | + | <li>Maximum wash loss of 0.5%</li> | 
| − | *A 100 mm layer of smaller grade pea gravel should be laid over the clear stone to reduce the chance of puncture damage to geotextile fabric. 
 | + | <li>Minimum durability index of 35</li> | 
| − |   | + | <li>Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions</li> | 
|  | + | </ul> | 
|  | + | {{:feedback}} | 
|  | [[Category:materials]] |  | [[Category:materials]] |