Astm | D4633

-values are typically corrected to a 60% efficiency standard, known as N60cap N sub 60

: The hammer is raised to its standard drop height and released, striking the anvil exactly as it would during a real SPT. astm d4633

Why is this important? Two different SPT rigs—using the same hammer weight and drop height—can deliver very different energy to the soil. Without energy measurement, your N-value (blow count) might be inconsistent. ASTM D4633 allows you to: -values are typically corrected to a 60% efficiency