Pocket penetrometers and hand vane testers are both used during ground investigations to make rapid assessments of cohesive soil. Although they are sometimes treated as interchangeable, they measure different properties and have different applications and limitations.
A pocket penetrometer provides a quick indication of soil consistency and an approximate unconfined compressive strength. A hand vane tester measures the torque required to shear cohesive soil and uses this to estimate undrained shear strength.
Choosing the correct instrument depends on the soil, the required result and how the information will be used.
The difference at a glance
Pocket penetrometer
- Provides an approximate indication of unconfined compressive strength
- Best suited to rapid logging and comparison of cohesive soils
- Can be used on suitable samples and freshly exposed soil surfaces
- Compact, economical and quick to operate
- Should be regarded as an index test rather than a source of design parameters
Hand vane tester
- Estimates undrained shear strength from the torque required to cause soil failure
- Best suited to soft-to-firm cohesive soils
- Can allow peak and remoulded strength to be compared
- Provides a more direct assessment of undrained shear strength
- Results remain dependent on equipment, soil conditions and test procedure
Neither instrument is suitable for every soil type, and neither should replace an appropriately designed ground-investigation or laboratory-testing programme.
What does a pocket penetrometer measure?
A pocket penetrometer is a spring-loaded handheld instrument. Its piston is pressed into a prepared soil surface to the marked depth, and the resistance is read from the graduated scale.
It is commonly used during:
- Trial-pit logging
- Borehole and sample logging
- Preliminary assessment of cohesive-soil consistency
- Comparison of samples from different depths
- Selection of samples for further laboratory testing
The instrument is particularly useful when a geotechnical engineer or engineering geologist needs a quick, repeatable indication of changing soil conditions.
ASTM D8605/D8605M-26 describes the use of a pocket penetrometer on cohesive soils. Importantly, it categorises the method as an index test and states that its results should not be used to produce engineering design data.
Readings are generally most meaningful in relatively uniform, cohesive soils such as silty clay and clay. Stones, coarse particles, fissures, roots, surface drying and sample disturbance can all affect the result.
A pocket penetrometer is not suitable for loose sand, gravel or soil that readily crumbles when tested.
What does a hand vane tester measure?
A hand vane tester uses a set of blades that are carefully pushed into cohesive soil. The operator rotates the instrument at a controlled rate until the soil shears around the vane.
The measured torque is converted into an estimate of undrained shear strength, usually expressed in kilopascals.
A hand vane is commonly used for:
- Assessing soft-to-firm clay and cohesive silt
- Investigating changes in undrained shear strength with depth
- Testing suitable trial-pit exposures
- Checking suitable samples
- Comparing peak and remoulded soil strength
- Supporting the selection of samples for laboratory testing
Where the equipment and procedure permit, the soil may be remoulded after the initial test and tested again. Comparing the undisturbed and remoulded results can provide an indication of soil sensitivity.
The method is generally unsuitable for granular soils, very stiff soils or material containing gravel, shells, roots or other obstructions. These can prevent correct vane insertion or produce unrepresentative resistance.
Which test is more accurate?
It is more useful to ask which instrument is appropriate for the required assessment.
A pocket penetrometer provides a rapid empirical estimate. It is particularly helpful for logging, screening and comparing cohesive soils, but the small test area makes it sensitive to local variation and testing technique.
A hand vane measures the torque required to cause a shear failure around a known vane geometry. This provides a more direct estimate of undrained shear strength, but the result can still be influenced by:
- Vane dimensions and calibration
- Rate of rotation
- Soil anisotropy
- Fissures and inclusions
- Disturbance during insertion
- Partial drainage during testing
- The operator’s technique
A hand vane result should therefore not automatically be treated as a definitive design value.
How do the relevant standards apply?
For UK ground investigations, BS 5930:2015+A1:2020 provides current recommendations for planning, undertaking and reporting ground investigations. Pocket penetrometer and hand vane observations can support field descriptions and the wider ground model, but using an instrument during BS 5930-based logging does not mean the individual test is “BS 5930 compliant.”
ISO 22476-9:2020 covers formal field vane testing. A small handheld vane used in a trial pit or on a sample should not automatically be described as complying with this standard. Compliance depends on the equipment, test arrangement, calibration, procedure and reporting requirements.
BS 1377-7:1990 includes a laboratory vane procedure for determining the total-stress shear strength of soft-to-firm cohesive soils. The suitability of a particular handheld tester should be confirmed before claiming that results comply with this method.
ASTM D8605/D8605M-26 specifically addresses pocket penetrometer use on cohesive soils. It confirms the value of the instrument for rapid consistency assessment while making clear that the results are approximate and are not engineering design data.
Always follow the project specification, current edition of the relevant standard, equipment instructions and the organisation’s quality procedures.
When should you choose a pocket penetrometer?
Choose a pocket penetrometer when you need:
- A lightweight instrument for routine site logging
- Rapid comparison between cohesive-soil samples
- An approximate indication of consistency
- A convenient screening tool for trial pits and samples
- An economical addition to a field engineer’s kit
It is often the more practical choice for preliminary investigations and descriptive logging where a rapid index reading is sufficient.
When should you choose a hand vane tester?
Choose a hand vane tester when you need:
- An estimate of undrained shear strength in suitable cohesive soil
- Greater differentiation within soft-to-firm clay
- Peak and remoulded strength measurements
- An indication of soil sensitivity
- A more specialised assessment than a pocket penetrometer provides
The vane size must suit the expected soil strength, and the instrument should be properly maintained and calibrated.
Can the two instruments be used together?
Yes. On suitable cohesive soil, the two instruments can provide complementary information.
The pocket penetrometer can be used for rapid logging and comparison across a large number of samples. Selected locations or samples can then be assessed with a hand vane where an estimate of undrained shear strength is required.
Differences between the readings should be investigated rather than forcing the results to agree. Soil disturbance, fissuring, gravel, drying and differences in the tested volume can all influence the relationship.
Neither instrument replaces laboratory testing where reliable strength parameters are required for foundation, slope, embankment or earthworks design.
What about granular or very stiff ground?
Pocket penetrometers and hand vanes are principally intended for cohesive soils. They should not be used to assign strength values to sand or gravel.
For granular materials, compacted fill or pavement investigations, a dynamic cone penetrometer may be more appropriate. Dynamic penetration testing measures resistance to penetration rather than directly measuring undrained shear strength, so its results should also be interpreted using the appropriate procedure and correlations.
Frequently asked questions
Can a pocket penetrometer be used on sand?
No. Pocket penetrometers are intended for cohesive soils. Sand and gravel do not provide the confined, uniform material required for a meaningful reading.
Can pocket penetrometer readings be used for foundation design?
Not on their own. The instrument provides approximate index information and should not be used as the sole basis for engineering design.
Does a hand vane directly measure bearing capacity?
No. It estimates undrained shear strength in suitable cohesive soil. Bearing-capacity assessment requires appropriate ground-investigation data, engineering interpretation and consideration of the proposed foundation and ground conditions.
Does every hand vane test comply with ISO 22476-9?
No. Compliance depends on the equipment, test arrangement, calibration, procedure and reporting. A handheld vane should not automatically be described as an ISO 22476-9 field vane test.
How often should the equipment be calibrated?
Follow the manufacturer’s recommendations, project specification and your quality-management procedure. The instrument should also be checked before use for damage, free movement and a correct zero reading.
Selecting the right soil-testing equipment
The pocket penetrometer is usually the best choice for rapid logging and preliminary comparison. The hand vane tester is better suited to projects requiring an estimate of undrained shear strength in soft-to-firm cohesive soils.
The key is to match the instrument to the soil and the purpose of the investigation—and to recognise the limitations of the result.
Geo Site Supply provides specialist equipment for geotechnical investigation, soil assessment and field testing throughout the UK and internationally.
View the Pocket Penetrometer and Hand Vane Tester, or contact Geo Site Supply if you need help selecting suitable equipment for your application.