The classification of rock burst grade [37].

The occurrence of rockburst is closely related to the strength and stress conditions of rock mass. The Lalin Railway tunnel in China was taken as an example, the strength and stress parameters of rock mass at 22 rockburst locations were obtained by using the results of indoor and outdoor tests, including maximum in-situ stress, maximum tangential stress, uniaxial compressive strength of rock and uniaxial compressive strength of rock mass. These four parameters were then selected to form a rockburst grade evaluation index system. Furthermore, SSA (Sparrow search algorithm) and probabilistic neural network (PNN) were used to construct a rockburst grade evaluation network, and the sensitivity of rockburst grade evaluation parameters was therefore analyzed. It shows that SSA could determine the smoothness factor of PNN efficiently, and it is reasonable to use SSA-PNN framework to evaluate the rockburst grade; maximum tangential stress and uniaxial compressive strength of rock mass have the greatest influence on the accuracy of rockburst grade evaluation, followed by maximum in-situ stress, and uniaxial compressive strength of rock has the least influence on the accuracy of rockburst grade evaluation; integrated maximum in-situ stress, maximum tangential stress, uniaxial compressive strength of rock and uniaxial compressive strength of rock mass, the rockburst grade evaluation results are highly reliable. The results presented herein may provide important reference value for the rockburst grade evaluation and the selection of rockburst grade evaluation parameters.