Soil classification - Geotechnical Investigation and Design Tables - page 27

Figure 2.3 Soil and rock origins.

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The transporting mechanism determines its further classification:
- Alluvial - deposited by water
- Glacial - deposited by ice
- Aeolian - deposited by wind
- Colluvial - deposited by gravity
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Fill - deposited by man

2.18 Classification of residual soils by its primary
mode of occurrence

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Residual soils are formed in situ.

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The primary rock type affects its behaviour as a soil.

Table 2.18 Classification of residual soils by its primary origin (Hunt, 2005).

Primary occurrence Secondary occurrence Typical residual soils

Granite Saprolite Low activity clays and granular soils.

Diorite
Gabbro Saprolite High activity clays.

Basalt
Dolerite
Gneiss Saprolite Low activity clays and granular soils.

Schist
Phyllite Very soft rock.

Sandstone Thin cover depends on impurities. Older sandstones

would have thicker cover.

Shales Red Thin clayey cover.

Black, marine Friable and weak mass high activity clays.

Carbonates Pure No soil, rock dissolves.

Impure Low to high activity clays.