SPT (standard penetration testing) is a widely adopted ground investigation technique for use in evaluating the relative density of sands.

Key advantages of SPT testing are :

• simple

• no limit to the depth at which SPT tests can be undertaken, whereas CPT (cone penetration testing) can be limited by soil or rock strength, rod friction, and rig weight.

• provides a physical sample of the soils (clays silts sands or weathered rock) which have been tested.

• a substantial body of correlations between SPT ‘N’ values and a range of geotechnical parameters for soils of all types, but primarily the relative density of sand.

• widely used for assessment of the potential of sands for liquefaction.

  On the other hand, the key limitations of SPT testing are :

• the energy delivered by the SPT hammer to the drill rods can be very variable depending on hammer type, drill rod size, ground conditions and depth, and other factors that will cause the delivered energy to vary over time.

• marking the drill rods and recording SPT N blow counts are notoriously unreliable.

Pile Dynamics Inc. has developed the industry-standard SPT Analyzer, which measures the energy transferred into an instrumented SPT rod during a Standard Penetration Test (SPT). This permits the adjustment of the measured N-value to the normalized N60 for standard 60% energy transfer into the rods in accordance with ASTM D4633. Compensating for widely variable efficiencies from different SPT rigs and hammer types improves the reliability of soil strength estimates used in geotechnical designs. The SPT Analyzer uses a strain-gauged section of SPT rod with attached accelerometers to measure the energy transferred to the drill rods, in full compliance with ASTM D4633. ASTM requires that the energy transfer of each SPT hammer be checked at least yearly, or more for hammers subject to wear from frequent use, or rope and cathead hammers for which energy transfer may be operator-dependent.

Whereas the SPT Analyzer provides annual or more frequent ASTM-referenced hammer energy transfer verification, the non-contact PDM can be used routinely for every project and SPT test to provide

• unparalleled accuracy for SPT N blow counts

• identification of true seating depth

• assessment of the variation of effective N over the distance of a single test

• reliable projection of effective SPT N values for refusal cases

• energy transfer using force and displacement measurements*

• evaluation of ground shear wave velocity **

* (not ASTM compliant)

** (advanced feature in development)