A literature review revealed that most of the empirical equations introduced for determination of the uniaxial
compressive strength (UCS) of rocks based on the Schmidt hammer rebound number (N) are not sufficiently
reliable mostly due to the relatively low coefficient of correlations. This is attributed to the fact that in most
cases one formula is used for all types of rocks, although the density of rocks is introduced to the formulae in
some cases. On the other hand, if one specific relationship between N and UCS is introduced for one rock
type, the equation will yield a much higher coefficient of correlation. During a research program supported
by the Shahrood University of Technology, Iran, a third type of approach was considered. The study aimed
to establish a relationship between N and UCS of a rock mass under particular geological circumstances. As
an example, in this study, the immediate roof rock of coal seams in North-Eastern coal fields of Iran was
selected. In order to determine the N and UCS, a significant number of samples were selected and tested,
both in-situ and in the laboratory, and a new equation was established. The equation can be used to predict
UCS of the roof rock in coal extracting areas in this zone by performing simple in-situ Schmidt hammer
tests. It is predicted that such a procedure will be feasible for other geological conditions.