Introducing plastic zone and tangential stress into tunnelling strain rockburst prediction

This paper on a criterion for rockbursts is focused mainly on the stress concentration and gradient change of the tangential stress of the surrounding rock. Two parameters are introduced into tunnelling strain rockburst prediction: the radius of the plastic zone and the radial stress at the elastoplastic junction after excavating the surrounding rock. A new rockburst criterion is proposed based on the mechanism for throwing-type rockbursts and catastrophe theory. Meanwhile, a new multi-factor index for identifying rockburst classification is given based on rockbursts in actual engineering. The results show that there is a certain correlation between strain rockbursts and the plastic-zone radius and radial stress of the surrounding rock, which can be estimated using the mechanical parameters and stress distribution before excavation, whereupon strain rockbursts can be predicted. By dividing the rockburst interval through a large number of rockburst examples, the accuracy of the criterion reaches 80·36%, and the accuracy for moderate-to-strong rockbursts reaches 83·33%.