Review of the literature revealed that most of the empirical equations introduced for determination of the unconfined compressive strength (UCS) of rocks based on the Schmidt hammer rebound number (Rn) are not practically reliable enough as in most of the cases one formula is used for all types of rocks, although the density of rocks is introduced to the formulas in some cases. On the other hand, if one specific relationship between hammer rebound number and unconfined compressive strength is introduced for one type of rock, 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 express the relationship between Schmidt rebound number and unconfined compressive strength of a rock mass under a 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 Schmidt number and the unconfined compressive strength, 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 be feasible for other geological conditions.
