Permeability and its influence - Geotechnical Investigation and Design Tables - page 96

8.11 Typical hydrological values
•

Specific Yield is the % volume of water that can freely drain from rock.

Table 8.11 Typical hydrological values (Waltham, 1994).

Permeability

Material m/day m/s Specific yield (%)

Granite 0.0001 1.2 10 − 9 0.5

×

Shale 0.0001 1.2 10 − 9 1

×

Clay 0.0002 2.3 10 − 9 3

×

Limestone (Cavernous) Erratic 4

10 − 4

Chalk 20 2.3

×

4

10 − 5

Sandstone (Fractured) 5 5.8

×

8

10 − 3

Gravel 300 3.5

×

22

10 − 5

Sand 20 2.3

×

28

•

An aquifer is a source with suitable permeability that is suitable for groundwater
extraction.

•

Impermeable Rock k < 0.01m/day.

•

Exploitable source k > 1m/day.

8.12 Relationship between coefficients of permeability and
consolidation

•

The coefficient of consolidation (c v ) is dependent on both the soil permeability
and its compressibility.

•

Compressibility is a highly stress dependent parameter. Therefore c v is dependent
on stress level.

•

Permeability can be determined from the coefficient of consolidation. This is from
a small sample size and does not account for overall mass structure.

Table 8.12 Relationship between coefficients of permeability and consolidation.

Parameter Symbol and relationship

Coefficient of vertical consolidation c v k/(m v = γ w )

Coefficient of permeability K

Unit weight of water

γ w

Coefficient of compressibility m v

Coefficient of horizontal consolidation c h 2to10c v =

Coefficient of vertical permeability k v

Coefficient of horizontal permeability k h

=

2to10k v

8.13 Typical values of coefficient of consolidation
•

The smaller value of the coefficient of consolidation produces a longer time for
consolidation to occur.