Damage constitutive model and Brittle–Ductile index of cemented ultra-fine tailing backfill with different binders considering initial damage and strain damage effect

With the increasing application of cemented ultrafine tailing filling method, the research on mechanical properties of cemented ultra-fine tailings backfill (CUTB) is becoming increasingly significant. The constitutive model and brittle–ductile index evaluation of CUTB as important components of mechanical properties have a significant impact on the safety and stability of backfill mining area. In this article, two indicators of the initial damage coefficient caused by different binders and the strain damage coefficient caused by different curing ages were proposed to construct the damage constitutive model considering initial damage and strain damage effect. Combined with the proposed damage constitutive model of CUTB and existed brittle–ductile index of rock, an improved brittle–ductile index of CUTB was presented. Finally, the proposed damage constitutive model and improved brittle–ductile index of CUTB was verified and discussed. The results show that (1) the different binders have a significant initial damage effect on CUTB. The initial damage of OPC-CUTB was increased with the increase in curing age, while the initial damage of WSB-CUTB was declined with the increase in curing age. (2) The different binders have a significant strain damage effect on CUTB. The strain damage of WSB-CUTB was increased with the increase in curing age, while the strain damage of OPC-CUTB was decreased with the increase in curing age. (3) The improved brittle–ductile index can well reflect the initial damage and strain damage effect of CUTB with different binders. The WSB-CUTB is more brittle than OPC-CUTB. (4) The proposed damage constitutive model and improved brittle–ductile index can fully characterize the mechanical properties of CUTB with different binders. The research results provided important theoretical guidance and had an essential engineering significance for mine safety mining.