Strength Characteristics of Cemented Backfill: A Review of Current Coal-Focused Research and Innovations

Backfill mining is a key technique for achieving mine stratum control and synergistic disposal of solid waste. Cemented backfill, as the core bearing structure of the mined area, plays an essential role in ensuring engineering safety and promoting green mining practices. This review systematically explains the multiscale mechanisms of strength development in backfill and establishes a three-tier analytical framework based on “Materials–Environment–Structure”. At the material level, previous research has revealed the microscopic mechanisms involving hydration products and the interfacial transition zone (ITZ); at the environmental level, the coupling of multiphysical fields during strength evolution has become a focal point of study. The core challenge lies in the fact that large-volume backfill under field conditions, which forms layered structures, is anisotropic and exhibits size effects during sedimentation and processing stages, significantly controlling the macroscopic mechanical behavior. This is difficult to fully reveal through laboratory research focused on homogeneous materials. The authors provide a comprehensive review of experimental, simulation, and theoretical results, with a focus on revealing the controlling mechanisms of factors such as layered weak interfaces, inclined interfaces, and structural scale for backfill strength and failure modes. Moreover, the proposed “Materials–Environment–Structure” framework offers predictive potential for linking multiscale strength formation mechanisms with field-scale structural performance. The goal is to advance the understanding of strength from material constitutive models to structural responses, providing theoretical support for the development of strength prediction methods and structural designs suitable for engineering practice.