Numerical analysis of the stability of arched sill mats made of cemented backfill

Abstract

Sill mats made of cemented backfill are important structures largely used in underground mines to provide a safer working space, increase ore recovery and improve ground stability conditions. When large span sill mats are exposed at the base, flexure can take place and tension appears at the base center of the sill mats. As cemented backfill and other geomaterials usually have a strength smaller in tension than in compression, a common practice in field is to add reinforcement structures built with bolts and metal grids. The construction of these structures is expensive and time-consuming. In this paper, the use of arched sill mats is for the first time proposed as a new solution to reduce the occurrence of tension and increase the stability. Binder consumption and metal reinforcement can thus be reduced, resulting more economic design of cemented backfill sill mats. A series of numerical simulations have been performed to analyze the efficiency of arched sill mats in reducing the minimum required cohesion. For the stope geometry considered in this study, the numerical results show that arched sill mats exhibit an improved stability compared to traditional rectangular sill mats. The minimum required cohesion of sill mats increases as the sill mat span increases but decreases as the curvature of the sill mats increases. The overlying uncemented backfill has effect to decrease the stability of sill mats. The minimum required cohesion of sill mats increases with the thickness of the uncemented backfill above the sill mats. These results remain valid as long as the stopes are wide enough, and the prevailing failure mode of sill mats is tension by flexure. More work is thus necessary to establish a criterion for the application of this new concept to increase the stability of cemented backfill sill mats against the failure of tension by flexure.