Determination of instantaneous breaking rate by Geological Strength Index, Block Punch Index and power of impact hammer for various rock mass conditions

► In this study, the excavability of various rocks with impact hammer was investigated using Geological Strength Index (GSI), Power of impact hammer (P), Block Punch Index. ► We suggest new equations to predict performance of impact hammer for tunnel and slope excavation. ► Valuable results from which the users could benefit were obtained. In mining and construction industries, selection of appropriate excavation method and equipment significantly affects the project feasibility. In the selection, the most important parameters are the geomechanical properties of the rock mass in the excavation route as extensively reviewed in literature. The most widely used geomechanical parameter is uniaxial compressive strength (UCS). However, UCS laboratory test requires time consuming and expensive sampling and core sample preparation processes, which can be quite difficult or sometimes impossible for a weak rock material taken from foliated, laminated or thinly bedded rock masses of low Rock Quality Designation (RQD) values (0–20%). For these reasons, Block Punch Index (BPI) test, which has thus gained an importance for the last decade because of its simplicity, has become applicable to determine rock strength for highly-jointed and weak rocks of low RQD. BPI provides significant convenience particularly for laminated-foliated-anisotropic rocks. In this study, the excavability of various rocks with impact hammer was investigated using Geological Strength Index (GSI), power of impact hammer ( P), BPI. Valuable results from which the users could benefit were obtained.