91 / 2021-09-28 05:40:39

Time-dependent stability of side-exposed backfill influenced by the creep of rock walls

Side-exposed backfill,Stability,Time-dependency,Numerical modeling

Backfill has become an integrated part of most of modern underground mines. Its stability during adjacent stope excavation is a critical concern to ensure a successful mining operation in open stoping and drift-and-fill mining (Hassani and Archibald 1998; Potvin et al. 2005; Darling 2011). Traditionally, the stability analysis and strength determination of side-exposed backfill are made by considering a wedge model proposed by Mitchell et al. (1982) with stiff and immobile rock walls. The neglection of rock-wall closure was justified by some box instability tests with very soft backfill (i.e., made with 2.2% cement content and cured 2.5–5 hours) under undrained condition as shown by Liu et al. (2016). In practice, a cemented backfill is usually exposed after a sufficient long curing time (typically 28 days) in order to take advantage of the full development of strength. The backfill then can become much harder compared to its state after a curing time of several hours. The stresses and stability of side-exposed backfill can thus be affected by instantaneous rock-wall closure associated with adjacent stope excavation. This has been shown by Wang et al. (2021) through numerical modeling with FLAC^3D.

It is however well-known that rocks always demonstrate more or less creep behavior (Griggs 1939; Cristescu and Hunsche 1998; Wang et al. 2019). Time-dependent stope closure has been reported in underground mines (Malan 1999; Raffaldi et al. 2019). It is also well-known that the mechanical properties of cemented backfill change with time (Belem et al. 2000; Fall et al. 2007). In practice, instantaneous excavation and backfilling of a stope are impossible. There are always some intentional or unintentional delays between the excavation and filling of a stope, between the end of filling operation and exposure of the cemented backfill. Until now, however, there is no study on how the stability and required strength of side-exposed backfill are influenced by the time-dependent behaviors of cemented backfill and rock mass. To fill this gap, a series of numerical simulations were performed with FLAC^3D. The time-dependent stability of side-exposed backfill under the influence of creep deformation of rock walls was analyzed. A part of results about the effects of delayed filling time, curing time, and exposure time on the required strength of backfill will be presented and discussed.