Numerical Investigation of the Stress State in Inclined Backfilled Stopes

Evaluating the stresses in backfilled stopes constitutes a critical step for insuring underground mine safety and for analyzing backfill response. In recent years, the writers have presented several methods for conducting numerical and analytical investigations to assess the stress state in backfilled stopes. The results have shown significant stress transfer to the rock mass along stope walls which induces an arching effect. To date, most solutions have been developed for (sub-) vertical openings. In this paper, the results of an extensive numerical investigation on inclined stopes are presented. Emphasis is placed on the influence of stope geometry, backfill properties, and filling sequence on the stress distribution in the backfill. Results indicate that for a given stope geometry, the most influential factors are the backfill shear strength parameters (cohesion c′ and friction angle ϕ′), Poisson’s ratio μ, and dilatation angle ψ′. Some of these parameters not only affect the stress magnitude, but also the distribution pattern which is shown to also depend on the filling sequence. One of the main outcomes from this study indicates that increasing the value of c′ tends to change the mechanical response of backfill from that of a particulate material to that of a consolidated medium, with each layer responding somewhat like a bending beam under vertical loads. The numerical results are compared to others obtained in previous investigations and also to analytical solutions and experimental test results obtained on a physical model. These are discussed in relation to the effect of the influence factors and their implications for the analysis of backfilled stopes.