Modeling of hydraulic fracturing process in crystalline rock reflecting actual mineral distribution using FDEM based on extrinsic cohesive zone model

A grain-based model (GBM) replicating the exact mineral distribution of the experimental specimen was constructed, and hydraulic fracturing simulations were conducted using the finite–discrete element method (FDEM), enabling direct comparison with laboratory observations. To leverage FDEM’s ability to represent fracture surfaces explicitly, the GBM incorporated the mineral boundary geometries directly into the mesh. An extrinsic cohesive zone model (ECZM) was adopted to improve stress representation, and verification demonstrated that ECZM avoided the artificial stress oscillations characteristic of the Intrinsic CZM (ICZM). Simulations of Brazilian tensile strength tests and hydraulic fracturing tests exhibited both intergranular and transgranular cracking, producing tortuous fracture paths, and the resulting fracture metrics agreed with experiments. The analyses further revealed that fracture propagation pathways are controlled by the interplay between the stress concentration at the fracture tip and the local mineral strength. This framework provides a robust tool for investigating fracture processes in heterogeneous crystalline rock.