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Geomechanical behaviour of waste rock barricades and cemented paste backfills : experiments and modelling

Abstract : Precious metals (such as gold and silver), and base metals (such as copper and others) are mined from the underground by excavation, creating voids of various sizes called (stope) which are interconnected by galleries or drifts (for circulation and draw point). In the case of cut-and-fill mining, these voids are usually filled with cemented paste backfill (CPB) which is a mixture made of concentrator mill tailings, of a binding agent (e.g., cement) and mixing water. Since the CPB is placed in the liquid state (solid-liquid suspension) in the underground stopes, it is necessary to use a retaining structure to contain it during backfilling. This retaining structure is called a barricade and can be constructed from wood, concrete, bricks, shotcrete or from waste rock available underground and which come from the drift’s development. Barricades built from waste rock are the most common in Quebec and Canada because they are economical, readily available (underground) and promote water drainage during backfilling, which promotes self-weight consolidation of the CPB, and therefore, reduction of pore water pressure. To date, little information exists on the real in situ characteristics of these barricades (such as their grain size distributions, their failure strength, the probable mechanism of their rupture and the standard dimensions used) to support their design in a meaningful way to ensure the safety of workers and mining equipment, which would contribute to the reduction of the mining cycle, and consequently, to the increase of mining productivity. The work of this thesis project was based on physical and numerical modeling to better understand the complex geomechanical behavior of waste rock barricades. A reduced-scale physical model of a mine stope was developed and constructed from translucent plexiglass plates to simulate backfilling in underground mines. A specific methodology was developed for the execution of the tests: instrumentation of the reduced-scale model using pressure sensors (total and pore water), calibration of the sensors, filling of the reduced-scale model with CPB, continuous monitoring of the tests using high-definition cameras. The tests carried out have made it possible to highlight the main probable mechanism of rupture of the waste rock barricades, as well as the estimation of the maximum pressure at the time of their rupture. The effect of waste rock particle size distribution on the stability and integrity of waste rock barricades due to the CPB pressure was also analyzed. Part of the tests carried out on the reduced-scale model were modeled using the Geostudio 2018 numerical code (GeoSlope Intl.) through calibration with the experimental results. The results of the simulations performed reproduced well the general behavior observed during the tests on the reduced-scale model, but with a significant difference in the pressure values. Simplified analytical solutions based on limit equilibrium have also been proposed based on experimental observations for the stability analysis (with respect to sliding and friction) of waste rock barricades. Some recommendations were proposed to take this study further by including the effect of various factors (e.g., the position of the barricade in the drift or draw point, the viscosity, and the shear yield stress of the backfill or its solids mass concentration, the shear parameters of the waste rock barricades, the arching effect, etc.).
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Submitted on : Monday, March 29, 2021 - 2:39:27 PM
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  • HAL Id : tel-03184434, version 1

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Mutaz Nujaim. Geomechanical behaviour of waste rock barricades and cemented paste backfills : experiments and modelling. Civil Engineering. Université de Lorraine; Université du Québec à Abitibi-Témiscamingue, 2020. English. ⟨NNT : 2020LORR0195⟩. ⟨tel-03184434⟩

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