Energy dissipation characteristics of sandstone under triaxial extension with different confining pressures

• Under low confining pressure (10 MPa), tensile cracking dominates, while higher confining pressures (30–70 MPa) promote shear cracking, indicating a transition in fracture mode. • Elastic energy and dissipated energy increase linearly with input energy, revealing an energy distribution mechanism that governs fracture mode transition in triaxial extension. • Peak energy storage capacity is more sensitive to confining pressure than elastic energy conversion capacity, highlighting the role of confinement in energy accumulation. • The findings provide a fundamental energy-based understanding of excavation-induced spalling and rockburst, aiding in the formulation of engineering disaster prevention measures.