This book gathers the proceedings of the 3rd International Conference on Geomechanics and Geoenvironmental Engineering (iCGMGE), held in Sydney, Australia, on November 26-28, 2025. Contributions include a wide range of topics in geomechanics such as soil and rock testing and investigation, shallow and deep foundations, retaining structures, offshore geotechnics, tunnels and underground works, earthen constructions, constitutive and multi-physics modelling of soil and rock, geosynthetics and ground improvements, geoenvironmental engineering, buried infrastructures, numerical methods and back analysis, landslides and slope stability, soil dynamics and earthquake engineering, and rock mechanics.