Consequently, the consistency of the SPT N values is questioned, i.e., the ability of 6.1 Transferred Energy Efficiency and Correction Factors.
normalise SPT data from higher energy efficiency hammers to that from liquefaction assessment requires the SPT N-value to be corrected for.
An auto hammer is estimated to be about 80% efficient. 1.333 times more than a safety hammer. The N value needs to be corrected to a normalized N60. We find .
is reported as the SPT blowcount value, commonly termed “N”. S.S.C. Liao and R.V. Whitman, 1986, Overburden Correction Factors for SPT in Sand: In 1990, Clayton presented an expanded listing of SPT hammer efficiencies (Em) in: 8).