
Different types of correction  Correction factor 

Correction for hammer 

Donut hammer  0.5–1.0 
Safety hammer  0.7–1.2 
Automatictrip donut hammer  0.8–1.3 

Sampler correction 

Without liner  1.00 
With liner: dense sand, clay  0.80 
Loose sand  0.90 

Rod length correction 

Length > 10 m  1.0 
6–10  0.95 
4–6  0.85 
0–4  0.75 

Borehole diameter correction 

Hole diameter 60–120 mm  1.00 
150 mm  1.05 
200 mm  1.15 
Correction for overburden pressure, ()  , where 
Correction for fines content ()  , where FC = percent fines content (percent dry weight finer than 0.074 mm) and = SPT value for 60% energy ratio 
