Analytical solution for determining the required strength of a side-exposed mine backfill containing a plug

Abstract

Backfilling is well known in the mining industry. A basic issue associated with mine backfill design is the determination of the strength of the backfill required to maintain the stability of the backfill body upon removal of a side wall when an adjacent secondary stope is excavated. This task is usually accomplished using a solution proposed by Mitchell et al. in the early 1980s. Recently, this solution has been reviewed and a modified solution has been proposed. These existing solutions, however, were developed for a uniform backfill. In practice, mine stopes are usually divided into primary and secondary stopes. Primary stopes are often backfilled in two stages: a plug pour and a final pour. In many cases, the cement content of the plug pour is higher than that of the final pour. The positive effect of the stronger plug is neglected in both the original and the modified Mitchell et al. solutions. Here, a new analytical solution is developed for estimating the required strength of a laterally exposed backfill by taking the plug into account. The proposed solution reduces to the modified Mitchell et al. solution if the plug pour and final pour have the same cement content. If the plug pour has a cement content higher than that of the final pour, the required backfill strength calculated with the proposed solution is lower than the values estimated with the modified Mitchell et al. solution; the same conclusion can be drawn to the comparison between the proposed solution and the original Mitchell et al. solution when the bond cohesion along the side walls is close to the cohesion of the backfill. Furthermore, the proposed solution indicates that an optimal cohesion ratio between the plug and final pours exists: there is no benefit in using excessively high cement content in the plug pour. It is noted that the proposed solution is valid only for high, narrow backfilled stopes, solutions for low and wide backfilled stopes are under development.Résumé : Le remblayage souterrain est maintenant couramment utilisé par l'industrie minière. Une problématique de base associée à la conception du remblai minier est la détermination de la résistance nécessaire que le remblai doit atteindre pour maintenir la stabilité de la masse de remblai une fois qu'un mur latéral est retiré, par exemple lorsqu'un chantier secondaire adjacent est excavé. Cette tâche est généralement accomplie à l'aide d'une solution proposée par Mitchell et al. au début des années 1980. Récemment, cette solution a été revue et une solution modifiée a été proposée. Cependant, ces solutions existantes ont été développées pour un remblai uniforme. En pratique, les chantiers miniers sont souvent divisés en chantiers primaires et secondaires. Les chantiers primaires sont souvent remblayés en deux étapes, soit la mise en place du bouchon, et le remplissage final. Dans plusieurs cas, la teneur en ciment est plus élevée dans le bouchon que dans le remplissage final. L'effet positif du bouchon plus résistant est négligé dans la solution originale de Mitchell at a...

Use of Cemented Super-Fine Unclassified Tailings Backfill for Control of Subsidence

“…In order to calculate the required strength of CPB, a lot of models have been proposed and modified [29][30][31][32][33][34]. In general, the most widely used model is developed based on Mitchell et al [35] in 1982 using limit equilibrium analysis.…”

Analysis on Filling Ratio and Shield Supporting Pressure for Overburden Movement Control in Coal Mining with Compacted Backfilling

“…To solve the maximum deflection, we substituted φ = 82%, E1, E3, F1, F3, x = 8 m and y = 50 m into Equation (23). The relationship between the maximum deflection wmax and the shield supporting pressure p was as follows: Based on Equation (29), the curve of the maximum deflection of main roof versus shield supporting pressure was drawn using the Maple software, as shown in Figure 6.…”

“…To solve the maximum deflection, we substituted ϕ = 82%, E 1 , E 3 , F 1 , F 3 , x = 8 m and y = 50 m into Equation (23). The relationship between the maximum deflection w max and the shield supporting pressure p was as follows:…”

“…According to the simplified elastic-thin-plate mechanical model, the double sine series selected by Navier [23,24] was used to express the deflection equation of the plate:…”

An Investigation of the Uniaxial Compressive Strength of a Cemented Hydraulic Backfill Made of Alluvial Sand

“…To ensure safe production and successful application of the backfill, the required strength of the cemented backfill must be adequately evaluated. This strength can be calculated through the use of analytical solutions proposed by Mitchell et al (1982) [2], Aubertin (2012, 2014) [3,4], Li (2014aLi ( , 2014b [5,6], and Liu et al (2016) [7] for vertical cemented backfill exposures. For horizontal cemented backfill exposures, analytical solutions have been proposed by Mitchell (1991) [8], but are seldom used due to the indetermination of several parameters [9][10][11].…”