Correlation Between the Constant mi of Hoek–Brown Criterion and Porosity of Intact Rock

Rock strength parameters are substantially impacted by porosity. This paper proposes a new model for presenting the relationship between porosity and the ratio of the unconfined compressive strength to the tensile strength of rock. The correlation between porosity and the constant mi of the Hoek–Brown (H–B) criterion is studied. To consider the effect of porosity on the rock strength ratio, the H–B criterion is modified by incorporating porosity instead of the H–B constants mi and s. A series of uniaxial, triaxial and Brazilian tests are conducted on various types of rocks (sedimentary, metamorphic and magmatic rocks) to study the effect of porosity on rock strength characteristics. The modified H–B criterion provides a good representation of the effect of porosity on the failure envelopes of rock. The modified criterion can be used to estimate the porosity and strength parameters of rock.