Liquefaction Screening Assessment for As-placed Cemented Paste Backfill

M. Shahsavari, M. Grabinsky, R. Moghaddam

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

Session: Mining Geotechnics

ABSTRACT: on Screening Assessment for As-placed Cemented Paste Backfill M. Shahsavari University of Toronto, Toronto, Ontario, Canada R. Moghaddam Golder Associates, Toronto, Ontario, Canada M. Grabinsky University of Toronto, Toronto, Ontario, Canada ABSTRACT Over the last 7 years the University of Toronto has led the research project Geomechanical Design of Cemented Paste Backfill Systems, involving a unique series of extensive field monitoring programs encompassing more than 10 stopes and barricades at Barrick's Williams Mine, Xstrata's Kidd Mine, and Inmet's Cayeli Mine. The fieldwork was complemented by extensive laboratory characterization of the mines' backfill materials. Several unique aspects of this project relate specifically to the liquefaction potential of Cemented Paste Backfill (CPB). The issue of liquefaction potential of an underground mining stope filled with backfill is one that has often been cited as a design concern but has received relatively little detailed attention. Although this mine design problem is complicated by many factors as compared to a conventional one-dimensional analysis for geotechnical earthquake engineering, it is nevertheless instructive to start with a conventional form of analysis to see how a hypothetical one-dimensional deposit of backfill would respond to some prescribed base excitation. Such an analysis is undertaken in this paper for a cemented paste backfill. The results are first interpreted in the context of the hypothetical boundary value problem, and then the limitations of applying these analysis results to real backfilled stopes are considered. The results are compared to an often cited heuristic that 'once the backfill unconfined compressive strength reaches 100 kPa the material is not liquefaction prone.' Based on these analysis results it is indicated that cemented paste backfill is less prone to liquefaction than many practitioners appear to think it is, however the types of further research required to demonstrate this are considered. RÉSUMÉ Depuis les 7 dernières années, l'Université de Toronto a dirigé le projet de recherche la conception géomécanique de systèmes de remblayage de la pâte cimentée à l'aide d'une série de programmes de surveillance extensifs qui comprenait plus de 10 chantiers et barricades aux mines suivantes: la mine Williams de Barrick, la mine Kidd de Xstrata,et la mine Cayeli d'Inmet. Le travail de terrain a été supplémenté par une caractérisation en laboratoire des matériaux de remblayage des mines. Plusieurs aspects uniques de ce projet portent spécifiquement sur le potentiel de liquéfaction de remblai en pâte cimentée (RPC). La question du potentiel de liquéfaction d'un chantier d'exploitation minière souterraine remplie de remblai est une qui a été souvent cité comme un problème de conception, mais qui a reçu relativement peu d'attention détaillée. Bien que ce problème de conception de la mine soit compliqué par de plusieurs facteurs, par rapport à une analyse classique unidimensionnel géotechnique génie parasismique, il est néanmoins instructif de commencer avec une forme classique de l'analyse pour voir comment un dépôt unidimensionnelle hypothétique de remblai répondrait à certains excitation de base prescrit. Ce document présente une telle analyse pour un remblai en pâte cimenté. Les résultats sont d'abord interprétés par rapport du problème de la valeur de la limite hypothétique, puis les limites de l'application de ces résultats pour les chantiers remblayés actuels sont considérées. Les résultats sont aussi comparés à une heuristique souvent cite: "une fois que le remblai atteint une résistance à la compression non confinée de 100 kPa, le matériel n'est plus sujet a la liquéfaction." Sur la base de ces résultats d'analyse, le remblai en pâte cimentée est moins sujet à la liquéfaction qu'on pensait, mais plus de recherches sont nécessaires pour le démontrer. Les types de recherches nécessaires sont considérés ici. 1 INTRODUCTION The voids created during ore extraction (stopes) are filled afterwards using different materials. One of the materials that has gained popularity recently is cemented paste backfill (CPB). The filled stopes are subjected to a wide range of dynamic loads consisting of earthquakes, production blasts, and the last but not the least rock burst events. On the other hand, since the backfill material is highly saturated, in the case of a dynamic load it is susceptible to liquefy. However, liquefaction analysis of CPB is not possible through conventional geotechnical engineering approaches due to the formation of cement bonds. However, previous in-situ measurements and numerical analysis show that an extensive amount of pore water pressure is developed within the stope behind the

RÉSUMÉ: faction Screening Assessment for As-placed Cemented Paste Backfill M. Shahsavari University of Toronto, Toronto, Ontario, Canada R. Moghaddam Golder Associates, Toronto, Ontario, Canada M. Grabinsky University of Toronto, Toronto, Ontario, Canada ABSTRACT Over the last 7 years the University of Toronto has led the research project Geomechanical Design of Cemented Paste

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Cite this article:
M. Shahsavari; M. Grabinsky; R. Moghaddam (2014) Liquefaction Screening Assessment for As-placed Cemented Paste Backfill in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper424,author = M. Shahsavari; M. Grabinsky; R. Moghaddam,title = Liquefaction Screening Assessment for As-placed Cemented Paste Backfill ,year = 2014}