I have a question regarding hammers and SPT. I came across two types of hammers that are used by drillers, 140 lb and 300 lb. As we all know, standard hammer for SPT blow counts is 140 lb for a 30 in free fall. I was wondering about the 300 lb hammer. If we use a 300 lb hammer, what will the free fall be? Foundation Engineering Handbook says it is 18 inches. In that case, will the blow counts represent the same soil type or resistance as is done in the Standard penetration test? Is N-value from 140lb-30in equivalent to 300lb-18in depending on the spoon size or is there a correlation between them?
They cannot be equal, but there can be a correlation between the standard and any other penetrometer for that matter. That is why it is designated a standard. Any other penetrometer could have been designated standard. However if a penetrometer other than the standard is used in a given terrain the relative consistency of the soils in profile could always be evaluated.