Effect of the cement–tailings ratio on the shear failure mechanism at the cemented tailing backfill–rock interface: Insights from the morphology of stope surrounding rocks

• Decreasing cement–tailings ratio reduces both compressive strength of CTB and shear strength of CTB–rock interface, while increasing failure area and reducing roughness of the new interface. • Digital image correlation identifies compressive stress concentration at obtuse angles relative to shear direction as the primary trigger for CTB failure. • Silicon particles are more prone to failure in wear areas, as confirmed by correlation between wear area and silicon-dense regions. • Findings support optimizing cement content in CTB design: lower cement can be used when horizontal principal stress is high, improving cost-efficiency and stability.