Volume 28, Issue 1 (January 2005)
An Assessment of the Effect of Rod Length on SPT Energy Calculations Based on Measured Field Data
The penetration resistance of a sandy soil, as measured by the Standard Penetration Test (SPT), is extensively used in geotechnical engineering. There are many factors that influence the energy transmitted to the rod string and sampler by the impact of the hammer on the anvil and thus affect the value of the blow count or N-value. This paper presents the results of a series of site investigations performed in northwest Turkey following the 1999 Kocaeli earthquake, where close to 2000 direct measurements of the energy transmitted by the hammer to the sampling system were conducted. It was found that short rod lengths have a small influence on the energy ratio when this is calculated by the force-velocity method. It was also observed that the N-value of the test interval has an influence on the effect that short rods have on the energy ratio calculated by the force-velocity method. Additionally, for this study the calculation of the energy ratio by the procedures outlined in ASTM D4633, which is currently withdrawn, is significantly greater than the energy ratio calculated by the force-velocity method.