SPT Hammer Efficiency Analysis

SPT hammer analysis is a geophysical method of measuring the amount of energy that is transferred from a SPT drop hammer to the drill stem (and subsequently to the SPT sampler).  SPT hammer analysis can be critical to the thorough evaluation of potentially liquefiable sand deposits.

The SPT analyzing equipment measures the hammer energy that is transferred to a standard drill rod section that has been instrumented with accelerometers and strain gauges and is linked directly into the advancing drill stem. Each time the SPT hammer strikes the drill stem, a force and acceleration are measured by the SPT analyzing equipment and are recorded for later data processing. The data output is later used to adjust the measured N-value to the normalized N60 for standard 60% energy transfer into the rods. Compensating for widely variable efficiencies from different SPT rigs and hammer types improves the reliability of soil strength estimates used in geotechnical designs.