Development of a novel equation for estimating the average volume of rock blocks in a rock mass with non-persistent joints

Accurate estimation of rock block size is crucial in geotechnical engineering, yet it often encounters challenges due to the complexity of modeling methods or the limitations of oversimplified approaches. This study introduces a novel equation that enhances the accuracy of rock block size estimation by incorporating joint persistence; an important factor frequently overlooked in existing models which describes the extent to which discontinuities split the rock mass. To this end, a three-dimensional discrete fracture network (DFN) was developed using 3DEC v.7.0 to model rock masses containing three non-persistent joint sets. The DFN model was carefully calibrated by removing boundary blocks and optimizing model sizes. The analysis of 125 distinct models led to the development of a practical correlation for estimating the size of rock blocks with non-persistent joints from an existing method for rock masses containing fully persistent discontinuities. The new equation, validated through cross-validation, offers a more reliable tool for practitioners, improving accuracy in rock block size estimation and supporting better decision-making in the field. The application of the newly developed equation to the Burgo Dam spillway in Australia was also shown to result in more accurate volume estimates than the existing methods.