A firm I once worked for required that blow counts from borings 20 feet or more in depth were required to be obtained using NW rods as opposed to AW rod. A study had found that a good deal of hammer drive energy can be lost in the sidewall of the boring depending on the depth and firmness of the soil being sampled. Is that an issue today?
I don't think I that this precaution would be necessary as long at the hammer had a "calibration" or documented energy measurements to determine the energy correction factor relative to N60 blow counts. This is a service that my company performs and I made a video for an overview of the measurement method if you are interested in checking it out. th-cam.com/video/i1DJbMS49jw/w-d-xo.html
A firm I once worked for required that blow counts from borings 20 feet or more in depth were required to be obtained using NW rods as opposed to AW rod. A study had found that a good deal of hammer drive energy can be lost in the sidewall of the boring depending on the depth and firmness of the soil being sampled. Is that an issue today?
I don't think I that this precaution would be necessary as long at the hammer had a "calibration" or documented energy measurements to determine the energy correction factor relative to N60 blow counts. This is a service that my company performs and I made a video for an overview of the measurement method if you are interested in checking it out. th-cam.com/video/i1DJbMS49jw/w-d-xo.html