7.3Permeability Characteristics
Field test: Collect a handful of representative soil material, discarding particles larger than 10 mm in diameter. Spray a fine water mist evenly throughout the soil particles to achieve the optimum moisture content. Mould the moist sample by hand pressure. The soil material is considered relatively impervious if the moulded sample remains intact after being tossed lightly from one hand to the other. The soil material is considered relatively permeable if there is difficulty in maintaining the moulded shape or the moulded sample crumbles after being tossed lightly from one hand to the other.
Permeable soils: Generally coarse grained soils including sand, gravel, sand-gravel mixtures. A soil is of basic type sand or gravel if, after the removal of any cobbles or boulders, over 65% of the material is of sand and gravel sizes.
Impermeable soils: Generally fine grained soils including clay, silt, gravelly or sandy clay, gravelly or sandy silt. A soil is of basic type silt or clay if, after the removal of any cobbles or boulders, over 35% of the material is of silt and clay sizes.
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