THE EFFECTS OF HAMMER-ROD ALIGNMENT AND ROD LENGTH ON SPT HAMMER EFFICIENCY

2021-12-6
Çevik, Mustafa Efekan
The Standard Penetration Test (SPT) is the most widely used in-situ dynamic penetration test to identify the geotechnical properties of mostly cohesionless soils for over 100 years. Although ASTM defines the procedure of the SPT, the test itself has special variabilities due to many uncertainties. It can be seen that, with different equipment and operator, one can obtain significantly different SPT-N values that belong to the same soil profile. To minimize this difference, some correction factors are used. The energy efficiency of the SPT hammer has been investigated since the 1970s. Two different energy measurement methods are used to calculate the energy transfer ratio: the force square (F2) method and the Force-Velocity (FV) method. The F² method was instated to ASTM D4633 in 1986 and withdrawn in 1995. ASTM D4633 was reinstated in 2005 using the FV method and used ever since. Nowadays, the only energy measurement method is the FV method; however, one of the most widely used energy correction publication, NCEER-97, is prepared on the basis of findings with the F2 method. In the present study, the effect of hammer-rod alignment on the hammer energy ratio has been studied through a set of in-situ tests, where SPT hammer efficiency is monitored. Additionally, available data from literature is compiled. On the basis of these, it is concluded that the hammer-rod alignment has an essential effect on the delivery of the energy ratio. With the increasing eccentricity of hammer anvil contact, energy efficiency decreases. Additionally, energy efficiency decreases with decreasing hammer rod length. This decrease is observed to be less than what is recommended by NCEER-97. As the concluding remark, a series of recommendations are listed to assess the energy ratio values for safety and automatic hammers along with the effects of SPT rod shorter than 10 meters.

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Citation Formats
M. E. Çevik, “THE EFFECTS OF HAMMER-ROD ALIGNMENT AND ROD LENGTH ON SPT HAMMER EFFICIENCY,” M.S. - Master of Science, Middle East Technical University, 2021.