SPT ENERGY MEASUREMENTS WITH THE PDA

The Standard Penetration Test (SPT) has long been the most common method of subsurface sampling for geotechnical exploration. The SPT provides a sample as well as information on the properties of the soil in the form of penetration blow counts. However, inconsistencies within the testing procedure itself, such as variations in a hammer type and operator variables can have a large effect on the results of the test. The Utah Department of Transportation has conducted a series of SPR hammer energy measurements on a number of hammers using the Pile Driving Analyzer (PDA) to correct the results of the SPT test. The hammer energy was recorded for each blow during the SPR test and the average and standard deviation were calculated for each set of blows. The hammer energies were then corrected to a hammer delivering 60% of the theoretical energy for the system using the average recorded hammer energy. Longitudinal studies of SPT hammer energies indicate that energies can change over time and SPT hammer energies should be checked periodically.