Panda Penetrometer Testing

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Corehard have employed the use of ultra-light dynamic cone penetrometers to provide resistance values in relation to existing or imported materials. As a result these devices have two primary uses.

1. Unbound materials or soils investigation: This is applicable to investigations on existing ground and will provide accurate information in relation to the following.

• Preliminary investigations (road structures, trenches, river banks, railway cuttings, etc)
• Soil studies (buildings, pylons, masts, structures, etc)
• Diagnosis and assessment (Moisture content, voids, material layers, disorders, etc)
• Site investigations with remote or restricted access
• Monitoring of embankment stability

2. Control of compaction

• Quality control of reinstated backfills
• Layer thickness monitoring
• Compaction homogeneity
• Trench or excavation backfill compaction
• Compaction control of all types of embankments (roads, rail, earthworks, dams, dykes, etc)

The device provides results throughout depth of penetration and will identify layers within structure of materials to be tested. Output from the device will provide standard results in MPa but can be converted to KN, psi, and CBR at any given depth through penetration. Conventional test methods such as  deflectometer plates, and impact hammers will only supply results from depths proportional to a diameter of hammer or plate, and this will not account for anomalies beyond this effective depth due to dissipation of force. Such dissipation of force will also affect equipment and compaction should only be carried out in recommended layers and number of equipment passes as recommended by either a works specification or manufacturers recommendations for selected device. If prescribed layers or passes have not been applied the lower portion of backfill will retain excessive air and through an unknown amount of time will subside. This may be accelerated through dynamic loading such as traffic, but otherwise may only manifest at surface possibly years later through failure of surface reinstatement or subsidence.

This is why reinstatement of backfill materials should be tested in layers no more than 100 – 150mm thick when employing impact (Clegg) hammer to verify trench compaction. Otherwise surface modulus value will provide misleading results as compaction is not being tested or investigated where layers have not been applied and compaction has only been applied to finished backfill rather than individual layers or “compacted lifts”.

Examples of penetrographs correct and incorrect applications can be seen in the following:

Correct:    Recycled Granular 150mm layers – 50kg vibrotamper       Incorrect:  Recycled Granular 900mm layer – 50kg vibrotamper

• Standard DCP is a recognised method for measuring in situ strength of flexible road construction in all materials other than bound concrete or bituminous mixtures.
• For information on PANDA penetrometer please click here
• For further information relating to penetrometer testing services available, or to discuss your specific requirements please click here