A comparative understanding of variable SPT energy measurement in practice

Accurate measurements of hammer energy are essential for reliable interpretation of the Standard Penetration Test (SPT). While energy variability is well-documented, standards often recommend measurements at a few depths or assume rig efficiencies. In many countries, these measurements are rarely performed, and there is a lack of guidance on sensor specifications and measurement frequency. This study addresses these gaps through a two-phase investigation. First, a custom 2-channel system (using either a 5000g/10000g accelerometer) that measures Energy Transfer Ratio (ETR) simultaneously at both the anvil and sampler levels, was compared with a commercial 4-channel system (10000g accelerometers) that can only measure ETR at the anvil level. The extensive laboratory and field comparison confirmed the reliability of the simpler 2-channel system, with ETR differences typically within ±5%. The second phase involved a large-scale field study with the 2-channel system across 77 boreholes (314 SPTs) at five test sites. This revealed substantial ETR variability across different rigs, even under uniform soil conditions. Anvil and sampler ETRs ranged from 29% to 78% and 21% to 54%, respectively, highlighting significant energy loss along the drill rods. These findings highlight the value of depth-wise ETR measurements for improving SPT energy correction and support future refinement of current SPT practice/standards.