Knowledge Base
| PARTICLE SIZE DESCRIPTION OF GRAVELS AND INTERMEDIATE GRITS (THREE LAYER SYSTEM) |
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| Material | Description | ||||
| Gravel (When intermediate layer is used) | Max 10% greater than 12mm | ||||
| Min 65% between 6mm and 9mm | |||||
| Max 10% less than 2mm | |||||
| Blinding grit (intermediate layer) | Min 90% between 1mm and 4mm | ||||
| SIZE
RECOMMENDATIONS FOR GRAVEL WHEN BLINDING GRIT IS NOT USED (TWO LAYER SYSTEM) |
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| Performance factors | Recommendation | ||||
| Bridging factor | D15(gravel) < or = 8 x D85(rootzone) | ||||
| Permeability factor | D15(gravel) > or = 5 x D15(rootzone) | ||||
| Uniformity factor | D90(gravel) / D15(gravel) < or = 3.0 | ||||
| No particles greater than 12mm | |||||
| Max 10% less than 2mm | |||||
| Max 5% less than 1mm | |||||
| PARTICLE SIZE DISTRIBUTION OF THE USGA ROOTZONE MIX | |||||
| Particle size | Recommendation (by weight) | ||||
| Fine Gravel | 2.00 - 3.40mm | Max 3% | Max 10% | ||
| Very Coarse Sand | 1.00 - 2.00mm | ||||
| Coarse Sand | 0.50 - 1.00mm | Min 60% | |||
| Medium Sand | 0.25 - 0.50mm | ||||
| Fine Sand | 0.15 - 0.25mm | Max 20% | |||
| Very Fine Sand | 0.05 - 0.15mm | Max 5% | Max 10% | ||
| Silt | 0.002 - 0.05mm | Max 5% | |||
| Clay | < 0.002mm | Max 3% | |||
PHYSICAL PROPERTIES OF THE USGA ROOTZONE MIX |
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| Physical properties | Recommended range | ||||
| Total porosity | 35% - 55% | ||||
| Air-filled (non capillary) porosity | 15% - 30% | ||||
| Water filled (capillary) porosity | 15% - 25% | ||||
| Saturated hydraulic conductivity | > 150mm/hr | ||||
| All tests should be carried out as per current ASTM Standards | |||||
