Evaluating the Effects of Joint Set Properties on Laboratory Rockmass Analog Specimen Strength Using Bonded Block Models

At the field scale, rock formations are referred to as rockmasses, which contain sections of intact rock separated by pre-existing joints. Both properties of the intact rock and properties of the joints affect the strength of the overall rockmass. Testing the strength of rockmasses in the laboratory is difficult due to the required scale. As one alternative, small-scale rockmass analog laboratory specimens have been used to study the effects of jointing on rockmass strength. However, when using such specimens, the creation of complex joint geometries is extremely difficult. Therefore, numerical models of rockmass analog laboratory specimens can be used instead. The use of such models requires the assumption that a calibrated model of intact rock can predict the behavior of jointed models without further calibration; this assumption has only recently been verified. In this study, a previously developed bonded block model (BBM) of Blanco Mera granite was used to simulate rockmass analog laboratory specimens containing complex joint geometries. Sensitivity analyses were performed to investigate the effect of the friction angle, orientation, persistence, and number of joints on the specimen strength. Both the number of joints and joint persistence were found to have large effects on the model’s strength. The micro-mechanisms associated with failure were observed to vary depending on the joint geometry and some of the associated trends contradicted studies previously published in the literature. Notably, the increase in GSI of the rockmass specimen as a function of increasing block size was found to be significantly larger than previously published results suggest.