Sandstone is widespread in the upper crust and underpins many subsurface engineering and energy applications. Understanding its deformation and failure under stress conditions therefore remains essential. However, the micromechanical mechanisms governing damage evolution and failure transitions under confining pressure remain poorly understood, largely owing to limited experimental reproducibility and intrinsic sample heterogeneity. Discrete element method (DEM)-based digital rock simulation provides a promising way to interrogate micromechanical damage processes, yet contact-parameter calibration often relies on trial-and-error, yielding non-unique, scenario-specific parameter sets and limiting reproducibility and transferability. This study reconstructs a DEM-based digital rock using the mineralogical and microstructural features of sandstone from the Yanchang Formation in the Ordos Basin. Mineral-scale elastic modulus and fracture toughness were determined through nanoindentation and combined with semi-circular bend simulations of individual mineral phases to calibrate the micromechanical parameters of the digital rock. The calibrated parameters were validated against the Hoek-Brown strength criterion and mechanical responses under varying loading conditions, confirming their robustness and applicability. Using the physically informed calibrated parameter set, we performed pseudo-triaxial compression simulations of sandstone under different confining pressures. Spatiotemporal tracking of microcracks shows that higher confining pressure postpones intergranular tensile cracking and amplifies strain incompatibility at interfaces between soft and stiff minerals, which triggers intragranular tensile cracking inside stiff grains. Force chain analysis indicates a confinement-driven alignment and densification of load paths that homogenizes stress transfer and delays instability. Joint microcrack and acoustic emission statistics document a transition from tensile-dominated failure at low confinement to shear-dominated failure at higher confinement. The physically informed calibrated parameters provide a unified framework for digital rock simulations under similar conditions, demonstrating their potential for capturing the mechanisms of damage evolution and failure in rock under confining pressure constraints.
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