<p>The shear behaviour of cement-stabilised soil–structure interfaces controls load transfer and deformation in many geotechnical systems, yet the mechanisms governing bond degradation and force redistribution along the interface remain insufficiently understood. This study combines macroscopic direct shear tests with three-dimensional discrete element method (DEM) simulations to investigate the effects of cement content, water/cement ratio (w/c), and interface roughness on cement-stabilised sand–structure interfaces. Laboratory tests were conducted on uncemented and cemented sand specimens with 1–3% cement at w/c = 0.6, prepared at a constant porosity and cured for 28&#xa0;days. Interface tests were performed against a rough waterproof abrasive surface with <i>R</i>_<i>n</i> = 0.25 under normal stresses of 50–200&#xa0;kPa. The results showed that cementation increased peak and residual shear strengths, enhanced dilation, and promoted strain-softening behaviour. A bonded-contact DEM model was calibrated and validated against the macroscopic direct shear responses, while cement-bond properties were assigned from previously established micromechanical bond relationships. The validated model was then used to examine w/c = 0.3–1.5 and <i>R</i>_<i>n</i> = 0.25–1.0. Increasing <i>R</i>_<i>n</i> nearly tripled the peak shear strength, while reducing w/c from 1.5 to 0.3 increased peak and residual strengths by 41% and 32%, respectively. DEM-based micromechanical analysis showed that cementation increased coordination number and reduced shear band thickness, whereas rougher interfaces intensified strong force-chain development. This study provides a calibrated DEM framework for interpreting cement-stabilised interface behaviour within the investigated parameter range, offering improved mechanistic understanding and practical guidance for the design and modelling of granular and cemented particulate systems.</p> Graphical abstract <p></p>