Permeability and its influence - Geotechnical Investigation and Design Tables - page 94

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Pore water pressure u 2 measured at shoulder of piezocone.

•

Soil mixtures would have intermediates times.

8.6 Effect of pressure on permeability
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The permeability of coarse materials are affected less by overburden pressure, as
compared with finer materials.

Table 8.6 Permeability change with application of consolidation pressure (Cedergren, 1989).

Soil type Change in permeability with increase in pressure

0.1 kPa 100 kPa Comment

Clean gravel 50

×

10 − 2 m/s 50

×

10 − 2 m/s

No change

10 − 2 m/s 10 − 2 m/s

Coarse sand 1

×

1

×

Fine sand 5 10 − 4 m/s 1 10 − 4 m/s

× ×

Silts 5

×

10 − 6 m/s 5

×

10 − 7 m/s

Some change

10 − 8 m/s 10 − 9 m/s

SIlty clay 1

×

1

×

10 − 10 m/s 10 − 11 m/s

Fat clays 1

×

1

×

8.7 Permeability of compacted clays
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Permeability is a highly variable parameter.

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At large pressure there is a small change in permeability. This minor change is
neglected in most analysis.

Table 8.7 Laboratory permeability of compacted cooroy clays - CH classification (Look, 1996).

Stress range (kPa) 40-160 160-640 640-1280 1280-2560

Typical soil depth (m) 2.0-8.0 m 8.0 m-32 m 32-64 m 64 m >

Permeability, k (m /s) 0.4-70 10 − 10 0.4-6 10 − 10 0.2-0.7 10 − 10 0.1-0.4 10 − 10 × × × ×

Median value, k (m /s) 2 10 − 10 0.8 10 − 10 0.4 10 − 10 0.2 10 − 10 × × × ×

8.8 Permeability of untreated and asphalt treated aggregates
•

Permeability of asphalt aggregates is usually high.

Table 8.8 Permeability of untreated and asphalt treated open graded aggregates (Cedergren, 1989).

Aggregate Size Permeability (m/s)

Untreated Bound with 2% Asphalt

38 mm to 25 mm 0.5 0.4

19 mm to 9.5 mm 0.13 0.12

4.75 mm to 2.36 mm 0.03 0.02