Effect of Hammer Shape On Energy Transfer Measurement in the Standard Penetration Test

The authors are to be commended for designing and executing a carefully controlled laboratory study of the effect of hammer shape on SPT energy measurements. The repeatability of the force data presented in the paper indicates that the authors have achieved consistent hammer impact velocities and that factors such as loose rod couplings have been avoided. Further, the writers are not aware of any other studies during which simple, cylindrical hammers and a safety hammer have been dropped on exactly the same anvil and rod string (Fig. 16). In this manner, the authors have eliminated all significant variables other than the hammer shape and developed a useful apparatus for laboratory studies of hammer shape effects. The writers disagree, however, with the authors' interpretation of the energy data and their resulting conclusions.