Size-Dependent Mechanical Properties and Excavation Responses of Basalt with Hidden Cracks at Baihetan Hydropower Station through DFN-FDEM Modeling  
[PERSON]  
1 Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources, Changliang River Scientific Research Institute, Wuhan 430010, China; [EMAIL_ADDRESS] (C.D. ); [EMAIL_ADDRESS] (S.O.) 2 State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China; [EMAIL_ADDRESS]  
3 School of Civil and Hydraulic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China  
*Correspondence: [EMAIL_ADDRESS]  
Zhenjiang Liu  
is a natural heterogeneous geological material, ranging from primary defects, such as microcracks and micro-holes at the meso-scale; to hard structural planes, such as beddings, cracks, and joints at the macro-scale; and even to weak structural planes with a length of several hundred meters, such as dislocation zones and faults. In other words, the discontinuities have hierarchies and scales, remarkably influencing the mechanical properties and engineering stability of rocks. Brittle rock failure is a continuous fracture evolution process that constantly involves the closure, initiation, propagation, and coalescence of defects under various loads, eventually leading to material failure [5; 6]. Therefore, the exploration of the failure process and the evolution laws of the mechanical properties of hard rocks is important to thoroughly reveal the development mechanism of disasters, accurately guide warning systems, and effectively reduce the risk of high-stress-induced disasters. The mechanical properties of rocks exhibit a significant size effect due to the presence of discontinuities at different levels. Relevant research methods mainly include tests, theoretical analyses, empirical estimation, and numerical simulations, among which the synthetic rock mass (SRM) method, which combines conventional numerical models representing an intact matrix and a discrete fracture network (DFN) model representing discontinuities, has been the most commonly used for multiscale mechanical analyses in geotechnical engineering [7; 8]. These numerical simulation methods can be broadly divided into continuous methods, such as the finite difference method (FDM), finite element method (FEM), and boundary element method (BEM); discontinuous methods, such as the discrete element method (DEM) and discontinuous deformation analysis (DDA); and hybrid methods, such as the finite-discrete element method (FDEM). In particular, the FDEM has the advantages of both discontinuous and continuous numerical methods, owing to which it can effectively simulate the gradual transformation process of materials from continuous to discontinuous, representing an important simulation technology for particle fracture, fragmentation, and interaction in brittle geomaterials [9; 10; 11; 12]. Based on the SRM model combining a DFN model with multiple numerical software packages, such as the universal distinct element code (UDEC) and particle flow code (PFC), the size effect of the mechanical properties of rocks under different stress conditions, such as uniaxial compression, triaxial compression, Brazilian disc splitting, and direct shear, has been systematically investigated, yielding the corresponding equivalent mechanical parameters and representative elementary volume (REV) [13; 14; 15; 16; 17; 18]. An accurate understanding of the fracture evolution and failure mechanisms of hard brittle rocks is important to ensure the safety of construction projects in deep underground engineering.