A modified solution to assess the required strength of exposed backfill in mine stopes

Abstract

Backfilling contributes to the improvement of ground stability and reduction of ore dilution in underground mines. A critical issue for backfilled stope design is the required strength for the fill material. A practical solution to address this question was proposed by Mitchell and co-workers for stopes with an exposed face and a high aspect ratio (height H over width B). However, this solution is not directly applicable to stopes with a relatively low aspect ratio (H/B). Its application is also restricted by additional limitations on the strength along the fill-rock interfaces and the load applied on top of the backfill. In this note, the model proposed by Mitchell and co-workers is modified to provide an estimate of the required strength of backfill for various geometries, material properties, and surface loads. The modified Mitchell (MM) solution is validated against experimental results. Sample calculations with the MM solution are also presented and discussed.Résumé : Le remblayage contribue à l'amélioration de la stabilité du massif rocheux et au contrôle de la dilution du minerai dans les mines souterraines. Lors de la conception des chantiers remblayés, un aspect critique est la détermination de la ré-sistance requise pour le remblai. Une solution pratique pour répondre à cette question a été proposée par Mitchell et collaborateurs pour des chantiers avec une face exposée et un rapport hauteur sur largeur élevé. Cette solution n'est toutefois pas directement applicable aux chantiers relativement bas et larges (faible rapport hauteur sur largeur). D'autres restrictions limitent l'application de la solution, selon la valeur de la résistance le long des interfaces remblai-roches et la charge appliquée à la surface du remblai. Dans cette note, le modèle de Mitchell et collaborateurs est modifié pour fournir une estimation de la résistance du remblai pour diverses géométries, propriétés de matériaux et charges de surface. La solution de Mitchell modifiée (MM) est validée à partir de résultats expérimentaux. Quelques exemples de calculs avec la solution MM sont aussi présentés et discutés.

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.…”

“…However, this model has several limitations [30]: (a) it considered the cohesion of interfaces between backfill and side wall equal to that of backfill, which is contrary to experimental results obtained from Fall and Nasir [36]; (b) it neglected the shear strength along the interfaces between backfill and side/back wall; and (c) it did not consider the surface load such as miners and equipment. Considering the abovementioned disadvantages, Li and coworkers proposed a modified Mitchell model [29] and a generalized solution [30] for calculating the required strength of backfill with a vertical exposure. The three-dimensional model they used is shown in Figure 3.…”

Underground Cemented Backfill, a Design Procedure for an Integrated Mining Waste Management.

“…Considering a vertical stope with an infinite backfill thickness, the vertical stress exercised by the overlying backfill on the UCB sill mat can be calculated by Equation11 [19]. (11) Where σ v (kPa) is the vertical stress applied by the overlying backfill on the sill mat, B (m) is the span of the sill mat (or width of the stope), γ (kN/m 3) and ϕ (°) are, respectively, the unit weight and friction angle of the overlying backfill, and K (-) is the lateral earth pressure coefficient in the backfilled stope above the sill mat. As described by Mitchell (1991), four failure modes condition the sill mat stability; the failure can be a result of a flexural, sliding, rotational or caving mechanism.…”

Strength Characteristics and Failure Mechanism of Cemented Super-Fine Unclassified Tailings Backfill

“…Underground mine backfill technology, one of the most important mining methods in the world [1], has developed rapidly since 1960s [2][3][4][5] due to the fact that it can control ground collapse, reduce ore dilution, reduce risk of barricade failure and enable mine operations to lessen the quantity of wastes [6][7][8][9]. Currently, cemented past backfill (CPB), which is made of mill tailings generated by the mineral processing plant, a binding agent such as ordinary Portland cement (OPC), water and other additives, is the most frequently used filling material due to its economic, environmental and technical benefits [10][11][12][13][14][15].…”