Brittleness determination of granites by Schmidt rebound hammer hardness to evaluate drillability

For estimating the rock strength and brittleness, Schmidt rebound hammer hardness value (SRH) is a useful and inexpensive technics. Brittleness depends on rock strength indicating the resistance of rock to elastic deformation. Since the direct methods for measuring of brittleness were not standardized, indirect methods such as Schmidt hammer were used in engineering geology. For this purpose, Schmidt rebound number, uniaxial compressive strength and Brezilian tensile test of seven granite rocks outcrops in Borujerd area were measured. Also, B1, B2, B3 and B4 concepts of brittleness and brittleness index (BI) as well as their relations with Schmidt rebound hammers hardness value (SRH) of the rocks were determined (in natural water content). The results show a good positive corrolation among Schmidt rebound hammers hardness value (SRH), brittleness index (BI) and brittleness concepts of these rocks(r2>0.7). Borujerd granites according to brittleness classificatoin system fall in to slighty brittle. The maximum and minimum brittleness index value in dry condition of rocks are 4.94 and 3.13, respectively. The study shows that the brittleness of the rocks decrease with an increase in water content. In saturation condition, the minimum brittleness concept(B4) is 5.27 Mpa. Monzogranites having B4
28 Mpa are very brittle and hard for drilling.