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Grain sizes and quick clay

Soils are sorted by grain size: clay, silt, sand and gravel. Clay has such small grains that it behaves completely differently from sand. Quick clay is clay that loses almost all its strength when disturbed, and it can cause large landslides.

S_t = \frac{s_u}{s_r}

sensitivity

d_{clay} < 0.002\ \text{mm}

the clay limit

Symbols

$S_t$	sensitivity
$s_u$	undisturbed shear strength	kPa
$s_r$	remoulded shear strength	kPa

Example

$s_u = 30$ kPa and $s_r = 0.5$ kPa:

$S_t = 60$ , a very sensitive clay.

A small slide in quick clay can trigger a much larger slide further back.

Practise soil and classification for free →

← Void ratio and porosity · Total stress and pore pressure →

Part of Geotechnical Engineering: Soil and classification.