Permeability

Constant Head Permeability in a Permeameter

Results given

Coefficient of Permeability

You provide

Remoulding conditions

Note: High degrees of compaction may not be possible since the material is remoulded into acrylic, not steel, cylindrical apparatus.

Typical use(s)

Determining permeability for soakaways etc.

Material required

• 2 kg for material up to 6.3 mm particle size
• 6 kg for material up to 10 mm particle size

Note: For material over 10mm particle size we would only be able to test by this method the material passing 10mm for a British Standard test, or include test material larger than this for a non-standard test. Depending on the mix of particle sizes, the non-standard test may give a more accurate reflection of the permeability of the whole material, but the larger than permitted particles may also give a large variability in measured permeability. It cannot be known if removing oversize material will increase or decrease the measured permeability. Removing occasional gravel from a sand would be likely to increase the permeability as large impermeable regions were removed. Removing medium and coarse gravel which had been the main constituents to leave only sand and fine gravel could well decrease the permeability by reducing the size of the interstices between the particles and so restrict the flow between them. A more suitable test for non-cohesive materials up to 37.5 mm particle size is the Horizontal Permeability test, but this typically requires 200 kg of material (enough to fill a box 1000mm long by 300mm square cross section).

Considerations

This test is suitable only for samples with relatively high permeabilities (coefficients in the range 10-2m/s to 10-5m/s: typically no finer than fine sand / coarse silt). Please see the note in the ‘material required’ section regarding oversize material. For lower permeabilities, usually when checking that the material is impermeable enough to meet a specification, the Triaxial Permeability is a more appropriate test.

K H Head Method

Results given

Coefficient of Permeability

You provide

• Remoulding conditions
• Cell pressure
• Differential pressure or hydraulic gradient (optional)

Typical use(s)

Ensuring permeability of landfill clay liner meets required specification.

Material required

• If remoulded, 2 kg for 100mm diameter specimen.
• If undisturbed,100mm diameter core-cutter or liner sample, at least 100mm intact length.

Notes

This test is not in BS1377, so the same notes as found in the Accelerated Permeability section apply.

“Accelerated” Permeability

Results given

Coefficient of Permeability

You provide

• Test specification.
• Remoulding conditions.

Typical use(s)

Indication of coefficient of permeability before a definitive British Standard Triaxial Permeability (BS1377:Part 6:Clause 6: 1990) is available.

Material required

• If remoulded, 2 kg (for 100 mm diameter specimen).
• If undisturbed,100 mm diameter core-cutter or liner sample, at least 100mm intact length.

Notes

By its nature, this test is non-standard and the client will need to ascertain for themselves the suitability for their purposes of the specification provided, and the acceptability of that specification by their client.
It is our experience that in the majority of cases, the British Standard Triaxial Permeability test does not take significantly longer than an accelerated method (see considerations on the triaxial permeability section), and it has the benefit of being a nationally accepted method.