Overview on theoretical calculation method of broken rock zone

The purpose of theoretical calculation of broken rock zone is to guide the design and construction of undergroundengineering project. Compared with the field measurement method and numerical simulation analysis,the theoreticalcalculation of broken rock zone is more convenient and faster. Two main theoretical calculation methods of brokenrock zone are systematically summarized,which are the strength criterion method and the mathematical modelmethod. The strength criterion method is mainly based on Mohr-Coulomb,Hoek-Brown and Druker-Prager theory. Usually,it can get a more accurate radius of broken rock zone by deriving the plastic zone radius,differentiating theboundary between broken rock zone and plastic zone,and modifying the parameter of rocks’ strength. The key is the boundary conditions of broken rock zone and the method to soften rocks. It also recommends that the calculation should be done by setting the stress gradient as the boundary condition,and adjusting the parameter of rocks by parametric inversion.Furthermore,the fundamental calculation of broken rock zone based on the dynamic and static mechanics ideas and the unified strength criterion is also briefly reviewed. The mathematical model method is based on the study of influencing factors of broken rock zone. Neural network models,support vector machine models,unascertained clustering models and multiple regression function fitting are commonly used in this method. The key is to determine the influencing factors,model selection and modeling. The focus of influencing factors selection is the secondary factors while the focus of model selection and modeling is to introduce other models to optimize the core elements of the original model. It recommends that the influencing factors should be selected according to local conditions,or the gray prediction model should be introduced,and then the model must be optimized by local database training and correction. In actual engineering project,as the strength criterion method is based on the circular roadway model under hydrostatic stress in homogeneous rock mass,the roadway radius,lateral stress coefficient and heterogeneous lithology will significantly affect the accuracy of calculation. On the other hand,the mathematical model method is restricted by insufficient consideration around influential factors and the existing database noise,which makes it difficult to improve the prediction accuracy. Combining with the field measurement technology,the size of broken rock zone fluctuates within a certain range within one cross section of the roadway and adjacent sections of the same roadway due to many factors,soany non-field-measured method cannot accurately predict the size of broken rock zone. In engineering applications,it is not advocated to determine the size of broken rock zone by theoretical calculation under the conditions that it is difficult to meet the assumptions of strength criterion method,or the unknown secondary factors have a significant influence on broken rock zone in mathematical model method. Future studies can be carried out from the perspectives of newstrength criterion derivation,a combination of multiple single prediction models and data iso-dimensional. Furthermore,the theoretical calculation of broken rock zone on various geological conditions in deep mine,and the rectangular or other irregular shape roadway should be focused on as well,under the condition of improving the prediction accuracy.