| [[File:Particle void ratio.png|thumb|The highest void ratio is found in uniformly graded aggregate, as there are no smaller particles to occupy the inter-particle pores. <ref name = Judge/>]] | | [[File:Particle void ratio.png|thumb|The highest void ratio is found in uniformly graded aggregate, as there are no smaller particles to occupy the inter-particle pores. <ref name = Judge/>]] |
− | [[File:Particle permeability.png|thumb|Higher permeability is found in larger, angular, uniformly graded aggregate. This is due to larger pore sizes and lower tortuosity. <ref name = Judge/>]] For advice on decorative surface aggregates see [[Stone]] | + | [[File:Particle permeability.png|thumb|Higher permeability is found in larger, angular, uniformly graded aggregate. This is due to larger pore sizes and lower tortuosity. <ref name = Judge/>]] |
| Gravel used for [[underdrains]] in [[bioretention]], [[infiltration trenches]] and [[infiltration chambers|chambers]], and [[exfiltration trenches]] should be 20 OR 50 mm, uniformly-graded, clean (maximum wash loss of 0.5%), crushed angular stone that has a void ratio of 0.4<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>. | | Gravel used for [[underdrains]] in [[bioretention]], [[infiltration trenches]] and [[infiltration chambers|chambers]], and [[exfiltration trenches]] should be 20 OR 50 mm, uniformly-graded, clean (maximum wash loss of 0.5%), crushed angular stone that has a void ratio of 0.4<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>. |