A novel joint element parameter calibration procedure for the combined finite-discrete element method

The combined finite-discrete element method (FDEM) has been widely used to simulate the fracture process of rock materials. The FDEM simulation requires many material parameters which should be calibrated through laboratory tests or directly cited from previous conclusions. However, it is difficult to obtain the joint element parameters, including the joint element penalty Pf and the type I and type II fracture energies GI and GII. Therefore, a novel calibration method for the above three parameters must be proposed. First, Pf can be obtained by uniaxial compression simulation, and Pf = 30E (E is Young's modulus) is applicable for homogeneous and isotropic rock materials. Second, an accurate GI value in the static loading state can be obtained by Brazilian disc simulation with a central preprepared failure path. Third, an accurate GII value can be calibrated by the modified variable-angle shear model. Finally, the GI and GII values with different element sizes can be calculated by the proposed linear equations. In addition, normal uniaxial and triaxial compression simulations can be used to verify the reliability of the calibrated GI and GII values. Moreover, the tunnel excavation simulation results show that the joint element parameters calibrated by the modified method can achieve cross-scale simulation, and the simulation results are more accurate.