ABSTRACT:

The success of open stope mining depends largely upon the ideal stope dimensions. If the stopes are made too large, this may cause severe problems such as dilution and increased rehabilitation costs, caving of hangingwall as reported in Zimbabwe's Gath's mine; and chimney caving occurring on Zambian Copperbelt mines. These occurrences can seriously jeopardize mine profitability and public safety. There are several methods currently available for stope optimization. The question that remains is - "which geometric layout provides the greatest recovery from the orebody assuring maximum geomechanical security and stability"? The paper discusses this question.

RESUME:

Le succes de mines a ciel ouvert en gradien depend fortanant des dimensions ideales des gradius. De trop larges gradius penvent etic respnsable de graves probleimes telle que l'erosion du mon suspendu entrainant de fortes depenses de rehabilisation, comme cela a etc le cas a la mine due GATH on Zimbabwe on encore de l'effeordiement des cheminees dans les mines du Copperbelt en Zambie. Tout cela remet en question la rentabilite et la rsecurite de la mine. Ilya flusiurs methodes d'optimilisation des gradient l'expose suivant e'tudie queles sort les organisations giometriques garantissant le plus grand rendement de minerai tout en assurant une securite geomechanique, maximode.

ZUSAMMENFASSUNG:

Der Erfolg beim offenen Kammerabbauverfabren hangt im wesentlichen vom richtigen Wahl der Kammerdimension. Sind die Kammern zu grop dimensioniert, so mup dem zufulge mit hahe Verdunnung/Verunreinmigung, hohe Wiederherstellosten, Bruchdes Hangenden (wie etwa z.B. Garith Grube in Simbabwe) und "Schornsteinantiger" Bruche (wie in "Kupfergurtel" des sanbisehen Bergbaugebiet) gerechnet werden. Diese Geschchen sind haufig mit hohen Wiederherstellkasten gebunden und beeintrachtigen die Sicherheit und Wirtschaftichbeit eimes Grubens. Dennoch gibt es in der Literatur einige Optimierungsverfahren zur Dimensionierung von Kammern aber bleibt nock unbeant-worted die Frage mach weiche geometrichen Vorrichtung gearbeiten werden soll lum moglichst der hochste Ausbeutefaktor und geo-mechanische Sicherheit und Stabilitait zu erziclen? Diese Articel befarst sich mit dieser Fragesterllung.

1.
INTRODUCTION

Stope and pillar mining is probably the oldest underground mining method having been developed by flint miners in Europe some 6,000 to 8,000 years ago (Temple 1972). This shows that ancient underground miners had learned the fundamental rules of stope and pillars mining to (1) leave sufficiently large ore pillars for roof support and (2) to limit the width of openings to minimize the possibility of roof falls. However, since the turn of the century, investigators have been trying to evaluate ore pillar strength by relating it to representative samples of ore tested in the laboratory and in the field.

2.
STOPE DESIGN INPUT DATA

The stope and pillar design is intimately tied to the geomechanical aspects. In a typical design practice the data base must, at least, include the general geology, intact rock properties, structural geological data, rock mass classification and in-situ stresses (i.e. loading conditions). Methods of determining the above data are available in several literatures. Generally, a great deal of input data are already available in the mine. However, the three main geomechanics database include the in situ stress analysis, field data base and laboratory testing. 2.1 In-Situ Stress A comprehensive description of fundamental of state analysis is documented in standard texts. The formation of stoping in an orebody causes stress distributions and an increase in pillar loading. Mining interest is usually concentrated on the peak-load bearing capacity of a pillar, when the rupture in the body of the pillar mass occurs. 2.2 Field Instrumentation Standard rock mass classification techniques should be applied to determine the strength and deformability of the fractured rock. For this purpose Barton's the NGI'Q' system and Bieniawski the RMR system should be used.

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