Evaluation of SPT Hammer Energy Variability

This report presents an evaluation of the Standard Penetration Test (SPT) hammer energy delivered to the SPT sampler during the performance of ASTM D1586, “Standard Test Method for Standard Penetration Test (SPT) and Split-Barrel Sampling of Soils.” Delivered kinetic energy was measured from SPT hammers from the Vermont Agency of Transportation (VTrans) and companies that do work for the State of Vermont. The variability of the measurements was assessed and a summary of the energy transfer ratios are provided. This report also supplies some guidance on recommended frequency of SPT hammer energy measurement on VTrans equipment. Nine different SPT hammer configurations were tested in this study. Variables included hammer type, drill rod type, drill rig type, operator, drilling method, and soil gradation. This study attempted to isolate these variables in order to quantify the contribution of each variable on the measured SPT hammer energy. A number of variables (e.g., rod type, soil gradation, groundwater condition) became evident as potential causes, but isolation of any one variable was difficult to do.