A 3D analytical solution for the short-term stress distribution in backfilled stopes and on barricades

Pengyu Yang, Li Li

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Mining Geotechnics

ABSTRACT: tical solution for the short-term stress distribution in backfilled stopes and on barricades Pengyu Yang and Li Li Department of Civil, Geological and Mining Engineering École Polytechnique de Montréal, Montréal, QC, Canada ABSTRACT Cemented paste backfill (CPB) is used to increase ground stability and ore recovery by underground mines worldwide. A key issue associated with application of CPB is to estimate the stresses in the backfilled stopes and on barricades. Recent numerical and experimental results showed that the critical moment for the safety of barricade is shortly after the placement of a CPB that still behaves like a fluid possessing a certain yield shear stress. This yield shear stress induced arching effect has never been considered in pressure estimation in backfilled openings. In this paper, a CPB shortly poured in a stope and barricade drift is treated as a Bingham fluid. A three dimensional analytical solution is proposed to evaluate the short-term stresses in backfilled stopes and on barricades. Sample calculations reveal that the yield shear stress induced arching effect is positively related with the backfill yield shear stress, fill height and barricade position, and negatively related with the cross sectional areas of the stope and drift. RÉSUMÉ Le remblai en pâte cimenté (RPdu terrain et augmenter le taux de récupération de minerai. Un aspect essentiel pour une utilisation sécuritaire du RPC dans un chantier remblayé et sur les barricades. Les résultats numériques et expérimentaux récents ont montré que du RPC lorsqu se comporte encore comme un fluide possédant un certain . . Dans cet article, le RPC peu après son versement dans un chantier est traité comme un fluide de Bingham. Une solution analytique tridimensionnelle est proposée pour évaluer les contraintes à court terme dans un chantier remblayé et sur les barricades est positivement lié au du remblai, à la hauteur du remblai et à la position de la barricade. Cependant il est inversement lié à l-section du chantier et des galeries. 1 INTRODUCTION The application of cemented paste backfill (CPB) has increased significantly with time in mining. CPB plays the role of assuring the stability of stopes, increasing ore recovery rate and minimizing ore dilution (Thomas et al. 1979; Singh and Hedley 1981; Hassani and Archibald 1998; Jung and Biswas 2002). It is also beneficial from an environmental standpoint as it reduces the surface disposal of mine wastes (Aubertin et al. 2002). Despite numerous advantages in application of CPB in underground mines, several cases of barricade failures reported in the literature (Helinski et al. 2006) indicate that the barricade design remains a serious concern. This challenge is closely related to the pressure estimation in the backfilled stope and on the barricade. To date, there are two types of analytical solutions used for barricade design. One is based on traditional overburden solution (OS). The other is based on stress transfer for partly or fully drained backfill. For a partly or fully drained backfill, upon its placement, CPB tends to settle down due to its own weight, inducing shear stresses along the fill-wall interfaces that in turn tend to hold the fill in place. Thus, the vertical stress can be reduced significantly with depth in the stope compared to that calculated with the OS. This phenomenon is known as arching effect, which is originally used by Janssen (1895) to address pressures in silos. In civil engineering, the arching theory has been largely adopted to estimate pressure distribution in backfilled openings like trenches (Marston 1930; Handy 1985) or above yielding structures (Terzaghi 1943). In mining engineering, it has been analysed numerically by the authors (Aubertin et al. 2003; Li et al. 2003; Li and Aubertin 2009a). Analytical solutions have also been proposed for estimating the stresses in a backfilled stope, mainly based on Marston (1930) solution. These include the extension of the Marston 2D solution to 3D stopes (Li et al. 2005; Pirapakaran and Sivagukan 2007), to 2D inclined stopes (Caceres 2005; Ting et al. 2011, 2014), and consideration of water pressure (Li and Aubertin 2009b, 2009c). Horizontal arching has also been taken into account for calculating the stress state in barricade drifts (Li and Aubertin 2009d, 2009e). The existence of arching effect has been further confirmed by laboratory results (Take and Valsangkar 2001; Ting et al. 2012; Sivagukan et al. 2013) and in-situ measurements (Belem et al. 2004; Thompson et al. 2009, 2012). While the arching solutions provide useful prediction of the stresses in backfilled stopes and on barricades, recent numerical and experimental results showed that arching may not take place shortly after the placement of the CPB in stopes (Thompson et al. 2009, 2012; El Mkadmi et al. 2013, 2014). Accordingly, the total (horizontal and vertical) stresses and (excess) pore water pressure in

RÉSUMÉ: analytical solution for the short-term stress distribution in backfilled stopes and on barricades Pengyu Yang and Li Li Department of Civil, Geological and Mining Engineering

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Pengyu Yang; Li Li (2014) A 3D analytical solution for the short-term stress distribution in backfilled stopes and on barricades in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper183,author = Pengyu Yang; Li Li,title = A 3D analytical solution for the short-term stress distribution in backfilled stopes and on barricades ,year = 2014}