An in-depth particle model study on the mechanical properties and fracture mechanisms of composite rock containing coplanar fractures under confining pressure

This research investigates how fracture configurations and confining pressures affect the failure and coalescence behaviors of composite rock. Using PFC 2D numerical simulation software, the mechanical behavior, failure mechanism, energy evolution law and acoustic emission (AE) patterns of fractured composite rock mass are studied. The findings show that increased fracture dip angles and confining pressures improve the rock's mechanical properties, whereas longer fracture lengths reduce its strength. The failure mode of rock primarily depends on the fracture dip angle and confining pressure, while fracture length and confining pressure significantly affect its integrity. With increasing fracture dip angle, the failure mode shifts from tensile to shear, and eventually to a combined tension-shear failure. Additionally, longer fractures and higher confining pressures lead to fewer macroscopic cracks and better sample integrity. The coalescence of a rock bridge is affected by the structural surface, confining pressure, and fracture dip angle. Micro-crack accumulation decreases with higher fracture dip angle and length but increases with greater confining pressure. Energy parameters and AE counts during compression vary based on fracture dip angle, length, and confining pressure.