A novel hydro-mechanical model for multi-fracture dynamic evolution using the numerical manifold method

• A novel Numerical Manifold Method (NMM)-based hydro-mechanical coupling framework is developed, integrating a hydraulic fracture network (HFN) seepage model for fully coupled simulation of fracture stress, aperture, and permeability evolution. • A multi-fracture evolution scheme is implemented to accurately capture propagation, intersection, and coalescence of hydraulic and pre-existing fractures under complex coupled conditions. • A dynamic seepage-path updating algorithm is proposed to efficiently update the hydraulic fracture network geometry during crack growth and fluid flow. • The proposed framework provides a robust and efficient numerical tool for analyzing fracture evolution and fluid-structure interaction in fractured rock masses. Accurate modeling of hydraulic fracture networks constitutes a core challenge in the numerical simulation of hydro-mechanical coupling failure in fractured rock masses. To address this, an improved hydro-mechanical coupling model based on the Numerical Manifold Method (NMM) is proposed. To significantly enhance the computational efficiency in handling dynamic fracture topologies, this study develops an optimized seepage path update algorithm. This algorithm automatically generates the flow net within the hydraulic fracture network (HFN), thereby substantially reducing the computational cost of seepage path retrieval. The model establishes an NMM global equilibrium equation that precisely couples fracture surface stress, fracture aperture, and permeability coefficient. This enables an integrated characterization of the stress field, fracture topology, and permeability during fracture network evolution. A set of benchmark cases validates the proposed hydro-mechanical coupling model, demonstrating high accuracy in simulating fluid flow and hydraulic fracturing. Building on this, the model is further utilized to analyze the failure process of fractured rock under water pressure, revealing how stress state and fracture network evolution influence the fracture mechanisms. Comparison with existing data confirms that the model can accurately simulate the dynamic propagation, complex intersection, and coalescence behaviors of multi-fracture in rock under hydro-mechanical coupling conditions.