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→Soil Volume
===Soil Volume===
===Soil Volume===
Each tree planted should have access to a minimum 30 m<sup>3</sup> of soil volume, including the growing medium within the tree pit and growing or structural soil medium below adjacent supported pavement. If more than one tree shares the same trench a minimum 20 m<sup>3</sup> of soil per tree may be acceptable.
Each tree planted should have access to a minimum 30 m<sup>3<sup> of soil volume, including the growing medium within the tree pit and growing or structural soil medium below adjacent supported pavement. If more than one tree shares the same trench a minimum 20 m3 of soil per tree may be acceptable. It should be noted that structural soils are mostly filled with rock and will therefore have much lower soil volumes. However, trees have been found to grow reasonably well in these soils because roots only occupy a portion of the total soil medium.
Structural soils consist of 3 components, mixed in the following proportions by weight: a load bearing stone lattice, soil, and a tackifier. Soils may be clay loam or coarser textured soil if drainage is a priority. Common tackifiers include ‘hydrogel’, a coated potassium propenoate-propenamide copolymer) or ‘stabilizer’, a plant based organic product sourced from the US.
*Crushed [[stone]] (granite or limestone) should be narrowly graded, highly angular with no fines. Stone sizes may vary between 20 to 75 mm. In British Columbia, a larger 75 mm stone (range between 60 and 80 mm) is used because it was found to allow for larger soil volumes (up to 33% of the total soil medium volume).
*[[Geotextiles]] are used with structural soils to prevent migration of fines from the road or sidewalk base into the structural soils. In BC, a Nilex 4545 fabric is used for this purpose, but other fabrics may also be suitable.
*Compaction to 95% SPD is achieved in 1 m lifts to 95% SPD. Testing of compaction of levels is accomplished with a trolled nuclear densometer for larger rock size mixes.
===Modular Soil Support Systems===
===Modular Soil Support Systems===