Permeability and its influence - Geotechnical Investigation and Design Tables - page 91

Permeability and its influence

8.1 Typical values of permeability
•

The void spaces between the soil grains allow water to flow through them.

•

Laminar flow is assumed.

Table 8.1 Typical values of coefficient of permeability (k).

Soil type Description k, m/s Drainage

Cobbles and boulders Flow may be turbulent, Darcy's law may not be valid 1

10 1
10 2
10 3
10 4
10 5
10 6
10 7
10 8
10 9
10 10
10 11
10 12

Very good

Gravels Coarse Uniformly graded coarse

aggregate

Clean

Gravel sand mixtures Clean Well graded without fines

Good

Sands Clean, very fine

Silty
Stratified clay/silts

Fissured, desiccated,
weathered clays
Compacted clays - dry of
optimum

Silts Homogeneous below

zone of weathering

Poor

Clays Compacted clays - wet of

optimum

Practically
impermeable

Artificial Bituminous, cements stabilized soil

Geosynthetic clay liner / Bentonite enriched soil
concrete

•

Granular material is no longer considered free draining when the fines > 15%.

•

Granular material is often low permeability (if well compacted) when the fines
>

30%.

8.2 Comparison of permeability with various engineering
materials

•

Material types have different densities.

•

Materials with a higher density (for that type) generally have a lower permeability.