Multiscale investigation of shear mechanical behaviour in cemented soil–rock mixtures (CSRMs) regulated by matrix–block welding states

Soil–rock mixtures (SRMs) are characterized by heterogeneous structural features that lead to multiscale mechanical evolution under varying cementation conditions. However, the shear failure mechanisms of cemented SRMs (CSRMs) remain insufficiently explored in existing studies. In this work, a heterogeneous three-dimensional (3D) discrete element model (DEM) was developed for CSRMs, with parameters meticulously calibrated to examine the role of matrix–block interfaces under different volumetric block proportions (VBPs). At the macroscopic scale, significant influences of the interface state on the peak strength of CSRMs were observed, whereas the residual strength was found to be largely insensitive to the interface cementation properties. Pronounced dilatancy behaviour was identified in the postpeak and residual phases, with a positive correlation with both interface cementation and VBP. Quantitative particle-scale analyses revealed substantial heterogeneity and anisotropy in the contact force network of CSRMs across different components. A highly welded interface was shown to reduce the number of interface cracks at the peak strength state while increasing the proportion of tensile cracks within the interface zone. Furthermore, the welding degree of the interface was found to govern the formation and morphology of shear cracking surfaces at the peak strength state. Nevertheless, a reconstruction method for the shear slip surface was proposed to demonstrate that, at the same VBP, the primary roughness of the slip surfaces remained consistent and was independent of the interface properties. Based on the extended simulations, the peak strength of the weakly welded CSRMs progressively decreased with increasing VBP, whereas further exploration of the enhanced residual strength is needed.