Strain rate and size effects on the brittleness indexes of Carrara marble

The determination of rock brittleness is crucial in analyzing excavation efficiency, deep mining stability, geological hazards, while nearly all the previous studies on rock brittleness are conducted in the quasi-static loading regime or based on the quasi-static mechanical properties. But loading rate or strain rate can change the mechanical properties of rocks. In modern engineering, dynamic behaviours of rocks under high strain rates are considered more often. In the past seven decades, various quasi-static brittleness indexes were proposed and studied. However, the size effect on brittleness was not studied comprehensively. For some brittleness indexes, the suggested specimen size is even not given. The present research assesses seven major brittleness indexes by using the dynamic mechanical properties of Carrara marble to check the feasibility of the application of these quasi-static brittleness indexes into the dynamic regime. The size effect is also investigated by using three different specimen dimensions. The results indicate that some quasi-static brittleness indexes, which provide incorrect variation trends of dynamic brittleness, are not applicable in the dynamic regime. Specimen size shows only a limited influence on the dynamic brittleness indexes. Four dynamic brittleness indexes, which have better data stability, reliability and operability, are recommended by the present research.