SPT Borehole Diameter Correction Factor

[NBRY1]

Given that SPT is not an exact science:
Should one apply a borehole diameter correction factor, CB (other than 1.0) when determining the N60 value, if mud-rotary methods are used?
My understanding is that it is used to account for stress relief in the larger diameter borings due to overburden removal.

 

[emmgjld]

It used to be considered good practice to apply the assumed corrections over a range of expected depths, soil/soft rocks, drilling process/medium and sampling equipment/personnel. Then consider what is actually being accomplished and/or learned. Most of these answers come during the application process.

 

[GeoEnvGuy]

The correction factor for size increases at 6 inches. Mud rotary is usually less than 6 inches so the correction factor of 1 is appropriate.