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

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.