Comparative evaluation of Schmidt hammer test procedures for prediction of rocks strength

Uniaxial compressive and Brazilian tensile strengths (UCS and BTS) of rocks are considered important properties in the design of most the geotechnical projects that interact with rock such as slope stability and underground excavation. Measuring UCS and BTS using standard laboratory tests are time consuming, tedious and expensive. Moreover, it requires a large number of well-prepared rock cores that is often not, particularly in soft or highly jointed rock masses. For these reasons, indirect tests such as Schmidt hammer hardness (SH) can be used for prediction of UCS and BTS of rocks. There is a wide variation in the recommended SH test procedures by institutions and various researchers. The objective of this study is to evaluate the performance of SH testing procedures for prediction of UCS and BTS of rocks. For this, 22 sandstone samples from Qum Province, central Iran, were selected and their UCS, BTS and SH were determined. Using data analysis, correlation equations have been developed between UCS and BTS with SH. To check the validity of the correlation equations, a t–test was performed. Results showed that SH test procedures based on continuous impacts at a point reveals the lower values than that based on single impacts. Further, it was found that SH test procedures have different performance for prediction of UCS and BTS of rocks.