Forty-Year Review of the Hoek–Brown Failure Criterion for Jointed Rock Masses

The Hoek–Brown failure criterion has developed into the most widely used system for estimating rock mass strength in rock engineering. The reason lies in its unique framework for integrating the strength properties of intact rock and geological observations in the field. While the determination of intact rock properties from laboratory tests is relatively straightforward, quantifying the relevant geological characteristics remains challenging. Strength degradation relations play a central role in the Hoek–Brown failure criterion by downgrading the strength properties of intact rock, based on quantitative measures of rock mass quality and disturbance, to estimate the strength properties of the rock mass. In this independent review, the origin and evolution of the Hoek–Brown failure criterion and the associated strength degradation relations and rock mass characterization methods are discussed. Common methods for estimating rock mass cohesion, friction angle and deformation modulus are presented. The effect of parameter uncertainty on the reliability of estimated rock mass properties is investigated. Understanding the basis and development of the Hoek–Brown failure criterion is essential for proper use of the system within its limits of applicability and with realistic expectations of reliability.