A novel method to account for size effect in rock indentation test

Rock indentation is a basic process underlying the rock fragmentation in many engineering practices including drilling, mechanized tunneling and mining. The simple, well-reproducible and accurate rock indentation test has long been used to assess rock properties, yet as a laboratory testing method, it causes potential size effect that has to be accounted for. In this study, we proposed a simple but novel experimental procedure and theoretical model to account for size effect. The novel experimental procedure involves a subsequent indentation on the largest rock fragment after splitting of specimens resulting from the first indentation test. We performed indentation tests on specimens of three different rocks (granite, basalt and sandstone) in which the peak indentation pressure exhibited a clear size dependency. Furthermore, we proposed a theoretical model to account for the damage zone evolution, that is suitable for tests using the wedge-shaped indenter with a conical tip, the same as that from a standard point load test apparatus. Comparison between the theoretical predictions and experimental data showed a general well agreement, indicating the validity of the proposed method.