## 5 Conclusions  
In this paper, a numerical approach is developed for the effective generation of equivalent broken rock mass models, allowing for the investigation of mechanical behavior and the determination of REV size of given broken rock masses. A statistical program is built first to evaluate the geometry parameters of the target rock masses; the parameters are then inputted into a self-development numerical program to generate the discrete fracture network based on the Monte Carlo method. A distinct element modelling platform, namely 3 DEC, is applied in conjunction with the developed programs to form a complete DFN-DEM coupling network. The performance of the proposed approach is demonstrated through a numerical example, which evaluates the mechanical parameters and REV size of the surrounding rock of the main powerhouse at the Liyang pumped storage power station using cylindrical rock models. The determined REV size is verified by the RMSI that evaluates the REV size using cubic rock model. The numerical study yields the following conclusions:  
1. The average and variance values of the structural plane in the surrounding rock of the main powerhouse are 4.30 m and 3.45 m\({}^{2}\), respectively, and the average and variance of the structural plane dip angles are 51.42\({}^{\circ}\) and (27.93\({}^{\circ}\))\({}^{2}\), respectively. The count and length of fractures per unit area of the rock masses are 0.23 and 0.97 m\({}^{-1}\), respectively; the number of fractures per unit length of the rock is 0.58 m\({}^{-1}\); and the fracture area per unit length is 1.87 m\({}^{-1}\). 2. The mechanical parameters evaluated from five cylindrical models generated using the proposed approach are quite close, which suggests good stability and effectiveness of the method. 3. The REV size of the rock masses determined using the proposed approach is 5 m \(\times\) 10 m for the cylindrical rock models. This result is consistent with the REV size estimated by the RMSI method using cubic rock models, which demonstrates the validity of using cylindrical models to evaluate the REV size of broken rock masses. In general, the numerical approach developed in this study exhibits/demonstrates desirable effectiveness in modelling broken rock masses. Once the geometrical parameters of the fracture in the engineered rock mass are obtained, a numerical model reflecting the structural characteristics of the fractured rock mass can be constructed by using the Random Fracture Network Simulation Program to provide a basis for simulating and investigating the engineering problems of the fractured rock mass. In addition to 3 DEC, some other discrete element analysis platform, such as UDEC, can work in conjunction with the developed programs for modelling large-scale mass structures and analyzing corresponding engineering problems. However, due to the difficulty in directly measuring the mechanical properties of larger-scale rock masses, the accuracy of the approach can  
Figure 14: Size effect results of equivalent rock cube model: (**a**) cube-model of the equivalent rock mass; (**b**) the relationship between the REV size indices and the side length of the cube model. only be numerically evaluated. Future studies are expected to further validate the precision of numerical modelling methods for broken rock masses. Conceptualization, X.H. and C.S. ; Funding acquisition, X.H. and C.S. ; Investigation, X.H. ; Software, X.H. and J.J.; Validation, X.H. and S.L. ; Visualization, X.H. ; Writing--original draft, X.H. and S.L. ; Writing--review and editing, X.H. and J.J. All authors have read and agreed to the published version of the manuscript. The work presented in this paper was financially supported by the National Natural Science Foundation of China (Grants Nos. 41831278) and the Fundamental Research Funds for Zhejiang Provincial Universities and Research Institutes (Grants Nos. JX6311041223). Not applicable. The data presented in this study are available in article.