<p>The coupled effects of heterogeneous composition and block structure make it challenging to establish a generalized mechanical model for block-in-matrix (bim) geomaterials. In this study, the bim cell is introduced as a new unit to investigate the mechanical coupling behaviors of cohesive bim geomaterials. First, the structural features and experimental preparation of the bim cell are outlined, and the shear mechanical properties and failure surface of the bim cell were obtained through direct shear tests and laser scanning experiments. Additionally, a three-dimensional discrete element model of the bim cell was precisely constructed and calibrated to replicate the meso-failure process, and was applied in numerical tests of bim cells with varying block sizes. Based on experimental and numerical results, it was demonstrated that the mechanical behavior of the rock block is akin to the existence of a structural interface within the matrix, which significantly controll both the peak and residual strength mechanism. In the peak state, the mechanical effects of the block are primarily controlled by the block-matrix interface properties. Whereas in the residual state, the structural effects of the block gradually become prominent in the irregularity of shear-induced slip. Finally, the strength coupling law of the components has been discussed based on the construction of a mechanical unit. The core contribution of this paper lies in emphasizing the differences in the failure mechanisms of the bim geomaterials under different shear deformations, providing a solid meso-mechanical basis for the development of peak and residual strength models.</p>