Use of a reduced scale physical model of a mine stope for assessing waste rock barricades potential instabilities due to early age pastefill pressure

M. Nujaim, T. Belem, C. Auvray

Dans les comptes rendus d’articles de la conférence: GeoSt. John's 2019: 72nd Canadian Geotechnical Conference

Session: Mining

ABSTRACT: This paper presents a reduced scale physical model of a mine stope used to reproduce the underground stope backfilling practiced in some Canadian mines. The objective is to study the geomechanical behavior of the waste rock barricades in interaction with the mine backfill. The instrumentations along with visual observations and preliminary results are presented. The main results demonstrated that: i) the stability of barricade depends on the properties of the barricade (size, position, particles gradation and compaction) and the friction between the barricade and the drift walls; ii) for two backfills containing 76% and 70% of solid percentage (by weight), the volumetric strain after the self-weight consolidation inside the filling chamber varied from 2% to 10%, respectively. In addition, the results showed the importance of using shotcrete around the barricade especially at the top of the downstream side to close the gaps and bind the barricade particles, which improves the barricade stability.

RÉSUMÉ: Cet article présente un modèle physique à échelle réduite d'un chantier minier utilisé pour reproduire le remblayage de chantier souterrain pratiqué dans certaines mines canadiennes. L'objectif est d'étudier le comportement géomécanique des barricades de stériles en interaction avec le remblayage de la mine. Les instrumentations ainsi que les observations visuelles et les résultats préliminaires sont présentés. Les principaux résultats ont montré que: i) la stabilité de la barricade dépend des propriétés de la barricade (taille, position, gradation et compactage des particules) et du frottement entre la barricade et les murs de la galerie; ii) pour deux remblais contenant 76% et 70% de pourcentage de solides (en poids), la déformation volumétrique après la consolidation du poids propre à l'intérieur de la chambre de remplissage variait de 2% du béton projeté autour de la barricade, de la barricade. 1. INTRODUCTION Massive quantities of waste rock and tailings are produced and stocked in piles and tailings storage facilities during the operations of the mining industries. Acid mine drainage or contaminated neutral drainage can be generated when these wastes are exposed to atmospheric conditions, resulting in environmental pollution. Underground backfilling offers significant economic and environmental advantages to mining operations (Thomas 1979, Hassani & Archibald 1998, Potvin et al. 2005, Belem & Benzaazoua 2008). Of the three types of backfill currently used in the mining industry (rock fill, hydraulic fill and paste fill), paste fill appears to be the most successful and popular. Underground backfilling requires the construction of a barricade placed in drift (draw point) to retain the backfill in filling chamber (termed stope). Serious consequences can occur if barricades fail, such as damage to mining equipment, injuries or even death of workers. The barricade are usually made of permeable brick, fibrecrete, concrete (hydraulic fill), timber frame (hydraulic & paste fill), shotcrete (hydraulic & paste fill) or waste rock (paste fill) depending on backfill type (Belem et al. 2013). Barricades in waste rock are profitable and widely used in many underground mines because they are available during underground development (Belem et al. 2013). These barricades are still poorly documented (e.g., Li & Aubertin 2011, Yang et al. 2016) and must be properly designed to avoid any failure that could slow down mining production. Barricade analysis stability requires a correct estimate of pore water and total pressures in backfilled stopes and on barricades during the backfilling and shortly thereafter. After backfilling, the total stresses on backfilled stopes and on barricades can decrease drastically due to several phenomena, such as the development of the arching phenomenon, pore water pressure dissipation and the cemented backfill hardening. Through the literature, numerous analytical solutions, numerical modeling and in situ measurements have been proposed, in which each investigation has its advantages and limitations, but further investigations are needed to assess the critical backfill pressure on the barricade and its design procedure. A number of mine stopes were implemented with in-situ instrumentation (e.g., Belem et al. 2004, le Roux et al. 2005, Thompson et al. 2009, Helinski et al. 2010, Thompson et al. 2012, Hasan et al. 2014)to evaluate the PWP and total/effective stresses in stopes. Also, several reduced physical models of mine stopes have been used to study the distribution of vertical stresses (Sivakugan & Widisinghe 2013, Widisinghe et al. 2013, Widisinghe et al.

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