SYNOPSIS:

Maule mine successfully exploited their ore bodies with the sub-level caving method until recently when drilling crosscuts in one of the ore bodies started closing up prematurely, to the extent that the mine was losing draw points at a rate faster than new ones could be established. Based on a study of the mode of failure, the failure sequence and the variation in rock strength, a failure mechanism could be postulated. Based on this hypothesis an entirely new strategy for mining the remainder of the ore body could be formulated.

RESUME:

Maule exploitation sees gates avec success en utilisant la method de foudroyage par sous-niveau, mais recemment, des coupes en traverse dans la formation se sont farmers prematurement, en sorte queue la mine parfait des points de outrage plus rap dement quoin ne pluvial en enabler de novae. II sets reveled possible de pustule un mechanism de defaillance en analysant minutieusement Ie mode de defaillance, la sequence de la defaillance et la variation de la density de la roche. L'hypothèse qui en resulte a permis la conception dune strategic complètement nouvelle pour travailler les gates qui restent.

ZUSAMMENFASSUNG:

Die Maule Mine hat bisher ihre Erzkörper erfolgreich durch den Debauch der ‘sublevel caving’ Methode abgebaut. Letzthin aber, finger Bohrungskreuztunnel an, sich verfrueht zu schließen, und zwar in sachem Made, day die Mine ihre Zapfpunkte schneller verlor, als day nee ausgebaut werden konnten Aufgrund einer gruendlichen Untersuchung der Bruchart, der Bruchreihenfolge und der Variationen der Gesteinsfestigkeit, konnte ein Bruchmechanismus angenommen werden. Mit diesel Hypotheses konnte seine nee Strategie fuer den restlichen Abbau des Erzkörpers formuliert werden

1 INTRODUCTION

Increasing use is being made of computational methods to solve rock engineering problems. Computer modelling facilitates future mine design, back analyses, sensitivity analyses and comparative studies This trend is encouraged. However, in mining applications it is still at the rock face that the ingenuity of the rock engineer is tested to the full. Notwithstanding the best designs, unknowns not taken into account can result in major instabilities. It is then that the rock engineer has to use his observational and interpretive skills coupled to his experience to come up with rapid solutions in order that corrective actions can be initiated. The Maule case study demonstrates the use of empirical design techniques to generate long term solutions. Drilling crosscuts in a section of one of the ore bodies were deforming so rapidly that early closure of that particular operation became a distinct possibility. Because of the unknowns and the complexity of the geometry, the modelling approach held little promise of finding a solution. Instead the answers had to be found underground. By questioning production personnel, the failure sequence could be established and by coupling the sequence of events to actual failure observations it became possible to postulate a failure mechanism accounting for the failure. Once this was achieved a new strategy for mining the remainder of the ore body could be formulated. This strategy was accepted and implemented by mine management and today, nearly 2 years later, it can be reported that the new strategy was completely successful.

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