The Standard Penetration Test (SPT) is a widely employed soil exploration tool that involves using a SPT hammer to drive a split barrel sampler at the bottom of a drill string to obtain soil samples. The number of blows required to penetrate the last 300mm (1ft) is the “N value”, which is related to soil strength.
The SPT Analyzer Determines the Energy Transferred by SPT Hammers using Force and Velocity Measurements, for Improved Reliability of SPT N-values
Several different types of SPT hammers are used to conduct Standard Penetration Tests. Their varying efficiencies influence the N value. The measured N value is normalized by multiplying it by the ratio of the measured energy transferred to the rod to 60% of the theoretical potential energy. The normalization compensates for the variability of the efficiencies of different SPT hammer types, and improves the reliability of soil strength estimates used in geotechnical applications.