SPT Hammer Energy Measurements - Calibration

Since 2010 we have performed SPT Hammer Calibrations - energy measurements need to be performed on SPT hammers to be compliant with EN ISO 22476-3. ASTM D1586-08 recommends normalizing results from any SPT test using energy measurements. When these tests are performed to determine the liquefaction potential of sands, ASTM D6066-96(2004) not only recommends but mandates the normalization. ASTM D4633-05 states that the only acceptable method of determining energy for normalization of N values is by force and velocity measurements.

We use the latest and greatest version of the SPT Analyzer from Pile Dynamics. It determines the energy transferred by SPT Hammers using force and velocity measurements. From the data obtained from the SPT Analyzer, it is possible to adjust the observed raw N value to a normalized N60 value.

Practically all State and Federal projects require annual calibration and some projects are now requiring site specific calibrations. Different combinations of rigs, hammers, operators, and site conditions can cause variations in energy transfer. A different operator on the same drill, on the same day can produce different results. Therefore, we recommend conducting SPT energy measurements on every job site and keeping the same drill, hammer and operator for the duration of the project. It is also necessary to recalibrate if the drill has repairs, modifications or damage to the motor, hammer or drill rod.

The SPT Analyzer improves the reliability and accuracy of SPT N values

• Determines the Energy Transferred by SPT Hammers using Force and Velocity Measurements
• Conforms to American Society for Testing and Materials Standards (ASTM):
  • Energy measurements are recommended to normalize results (N-values) from SPT tests (ASTM D1586)
  • Normalization of N-values based on energy measurements are required when SPT results are used to determine the liquefaction potential of sands (ASTM D6066)
  • The only ASTM accepted means of determining energy for normalization of N-values is by force and velocity measurements (ASTM D4633)
• Assesses the efficiency and consistency of operation of the SPT hammer on rigs which may vary from rig to rig, operator to operator and job site to job site.
• Conforms to European Standard EN ISO 22476-3
• On large or critical projects, energy testing may verify SPT performance to allow for increased design confidence and economy, potentially saving the client time and money.
• Calculate normalized N60 from Force and Velocity measurements
  • Great potential benefit to industry
  • Better uniformity
  • Spot problem rigs
  • Improved soil predictions using normalized N60 values
  • Adjust procedures to get uniform energy