ABSTRACT:

Strength characteristics and failure behaviour of stopes and sill pillars in a number of Swedish mines have been investigated. An observational investigation methodology was adopted. Failure modes and failure sequences were mapped and documented, along with information on local geology, mine geometry and geomechanical parameters. Continuum and discontinuum numerical modelling was used to explore failure mechanisms, as well as to correlate failure with loading conditions. Results from this work evolved in the form of stress criteria for the onset of different modes of failures, qualitative illustrations of the failure processes for different geological scenarios, and quantitative mine-specific guidelines for design and modelling.

RESUME:

Les caracteristiques des contraintes et des ruptures du chantier d'abattage et des piliers horizontaux dans plusieurs mines suedoises ont ete examinees. Une methode d'etude d'observation a ete choisie. Le mode et les sequences de ruptures ont ete repertoriees et documentees, ainsi que des informations sur la geologie locale, la geometrie de la mine, et des paramètres geomecaniques, Une modelisation numerique continue et discontinue permis d'etudier les mecanismes de rupture ainsi que de correler la ruputre et les conditions de charge. Les resultats de cette etude ont permis de produire des critères de stress de la phase initiale de different modes de rupture, une illustration qulitative des processus de rupture pour differentes situations geologiques cIassiques et des lignes directrices quantiatives et specifiques pour chaque mine pour la Conception et la modelisation.

ZUSAMMENFASSUNG:

Festigkeitseigenschaften und Bruchverhalten wurden fuer einige Abbau und horizontaler Erzpfeiler in schwedischen Bergbaubetrieben studiert. Es wurde eine Untersuchungsmethodik gewahIt, bei der großes Gewicht auf empirische Beobachtungen gelegt wurde. Diese Methodik umfaßte die Kartierung von Bruchtypen und Bruchsequenzen sowie das Sammeln von Informationen ueber die örtlichen geologischen Verhaltnisse, Abbaugeometrien und geomechanische Parameter. Numerische Modelle wurden angewandt um Bruchmechanismen zu untersuchen und zu erklaren und um Bruch und Belastungen in Korrelation zueinander zu bringen. Das Resultat dieser Arbeit enthalt Spannungskriterien fuer die Initiierung unterschiedlicher Bruchtypen, qualitative Illiustrationen von Bruchprozessen fuer verschiedene typische geologische Bedingungen sowie eher quantitative grubenspezifische Richtlinien fuer die Dimensionierung und fuer numerische Modellberechnungen.

1 BACKGROUND

In 1987, the major Swedish mining companies, governmental research funding agencies, and leading manufacturers of mining equipment established, and jointly financed the G2000 program - a five year research and development program for the Swedish mining industry. Research activities within the G2000 framework have embraced several areas, including ore characterisation, rock mechanics and rock fragmentation. Activities within the rock mechanics field comprised a number of research projects, falling essentially into two categories:

  1. Projects addressing mine-specific issues, such as ground control problems in cut-and-fill mining at depth, and introduction of new large scale stoping schemes for selective mining.

  2. Projects aimed at improving design methods for rock reinforcement systems, pillars, and large hanging walls.

These are all, in various forms and combinations, vital construction elements in several underground mining methods. Progress in terms of both improving the fundamental understanding and developing practical design guidelines was therefore deemed important by the companies involved. This paper describes a project aimed at increasing the understanding of failure processes in sill pillars and stopes, and on that basis contribute to design guidelines applicable in mine planning. The project methodology is described and examples of results and applications are presented and discussed.

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