Evaluation of the stress state in two adjacent backfilled stopes within an elasto-plastic rock mass

Backfill is used in the mining industry to improve the stability of underground openings and reduce the environmental impact due to the surface disposal of mine wastes. A critical issue for the design of backfilled stopes is the determination of the stress state in the backfill and surrounding rock mass. In recent years, much work has been conducted to assess the stresses in isolated backfilled stopes. Recent work performed by the authors indicates that the stress distribution in a backfilled stope may also be affected by the excavation of an adjacent opening. So far however, simulations of neighbouring stopes have been based on an elastic behavior for the rock mass, which may not reflect its actual response (especially under large stresses). This paper presents key results obtained from numerical simulations of two backfilled stopes excavated in sequence in an elasto-plastic rock mass. The simulations results illustrate the effects of the non-linear rock mass response and of other characteristics including stopes geometry (size and spacing) and depth, natural stress state, and backfill properties. These results indicate that, although arching effects tend to develop in all narrow stopes, the stress distribution in adjacent openings can be quite different for elastic or elasto-plastic rock mass behavior. The results presented here also illustrate the similarities and differences between the behavior of a single backfilled stope and of two adjacent stopes, depending on the rock mass properties and overall characteristics of the system.