Numerical investigation of the stability of a base-exposed sill mat made of cemented backfill

Sill mats are important supporting structures commonly applied in underground mines for better recovery. They are used to help recover sill pillars in open stoping or to provide a safer workplace in underhand cut-and-fill mining. To fulfil these functions, the sill mat is typically cast with cemented backfill mainly consisting of mine tailings and binders. To ensure economic and safe mining, a critical issue is to estimate the required strength of the base-exposed sill mat following underneath extraction. So far, a few analytical solutions have been proposed for this purpose by treating the sill mat as an isolated bending beam with two fixed ends. However, previous numerical analyses have indicated that the response of the sill mat can be significantly influenced by the rock wall closures due to underneath extraction. This aspect is ignored by the existing analytical models. In this paper, numerical models are used to evaluate the stability of sill mats upon the underneath excavation. The influence of rock wall closure on the stability and the minimum required strength of sill mats is analyzed. Simulation results indicate that the apparent failure mechanism of the sill mat is caving or rotation, while its actual failure mechanism is crushing or shearing. Accordingly, the required strength of sill mats increases as the variation of studied influencing factors tends to increase the horizontal stresses in the sill mats, including the increase in mine depth, rock pressure coefficients and sill mat stiffness. In contrary, the increase in the span or thickness of sill mat and rock mass stiffness tends to decrease the horizontal stresses in the sill mat, thereby leading to a reduction in the required strength of sill mats. It is also concluded that the stress increase does not always mean an improvement or deterioration of the stability of the sill mats.

Mots clés

Sill mat; Cemented backfill; Minimum required strength; Numerical modeling; Stability