Rock engineering applications require a more efficient and dependable approach to estimating mode-I fracture toughness (KIC) than is currently available. Herein, we develop an empirical relation between mode-I fracture toughness and tensile strength according to data from laboratory tests and previous researches on several kinds of brittle rocks. The tensile strengths were determined from Brazilian disc (BD) specimens, and the mode-I fracture toughness data were determined from cracked chevron-notched Brazilian disc (CCNBD) specimens, as suggested by the International Society for Rock Mechanics (ISRM). In contrast to the previously published linear and exponential relations, our empirical relation exhibits dimensional unity between the two sides of the empirical formula, which is preferable in terms of both physical meaning and mathematical form. Furthermore, the previously published linear relations are only applicable in special cases premised on a uniform specimen radius. Using our proposed empirical relation, the mode-I fracture toughness of brittle rocks can be quickly estimated from the known tensile strength.

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