Analysis of cemented backfilled stopes in the Rodoretto Talc mine

The Rodoretto talc mine at Prali, near Turin in Piemonte, Northwest of Italy, is an underground mine that uses conventional cut-and-fill, underhand mining. The stopes are backfilled using a concrete mixture that includes waste rock. The mine is considering a new backfill strategy that will increase the content of waste rock in the backfill, widen the stopes and alternate backfilling of the stopes. 3D numerical analysis was done on the cemented backfill stopes to understand the stresses present and the viability of this new backfilling approach. The results show that the new backfill strategy can be adopted under specific configurations and geological wall conditions of the stopes. The dimensions of the exploitation site are 3 m x 3 m under talc and 4 m x 4 m under backfill. Currently, a minimum compressive strength of 6.1 MPa is required. However, 3D numerical analysis, modelled using the GTS-NX software, has shown that for a span of 4m, with one completely backfilled overlying level and under an overload of 1.5 MPa, the maximum compressive stress at the roof is approximately 3.5 MPa. For deeper levels simulated by two overlying backfilled levels, also under an overload of 1.5 MPa, the maximum stresses are less than 3.3 MPa. This demonstrates that the new backfilling strategy can be safely applied at deeper levels, with stopes spanning up to 8 metres. This will minimise the waste produced by the mine, prolong the life of the mine while ensuring safe, responsible and sustainable operating conditions.