ABSTRACT:

Rock engineering projects requiring successive decisions on the type and amount of support needed to keep excavations stable demand a reliable performance model to base those decisions. In the Germunde coal mine (Portugal) the preliminary selection of supports for a new level was made possible upon analysing the extensive results of convergence measurements obtained in two previous levels of the mine. A close correlation was found between 3 variables: the average convergence rate of the drifts (which represent their stability criterion), the rock mass classes of the formations intersected by the excavations and the density of support that had been installed. Using a mathematical relationship involving those variables a rational approach for the design and selection of supports was developed, which was applied to the subsequent mine operations, thus contributing to the minimisation of support costs with a simultaneous safety assurance. Because of the possible applicability of the method to other situations, it is described and illustrated in detail.

RESUME:

Les projets d'excavation souterraine necessitent de decisions sucessives sur Ie type et la quantite d' elements de soutènement à appliquer pour mantenir leur stabilite ce qui implique Ie besoin d'un modèle de prevision fiable. Dans la mine de charbon de Germunde (Portugal) la selection preliminaire d'elements de soutènement pour un autre niveau a ete faite apres l'analyse des resultats des mesures de convergence sur deux precedants niveaux de la mine. Une bonne correlation a ete trouvee entre 3 variables: la velocite moyenne de convergence des galleries (qui represente son critère de stabilite), les classes de massif rocheux traversees par les excavations et la densite de soutenement qui a ete installee en souterrain. En usant la relation mathematique entre ces variables on a trouve une methode de prevision pour choisir les nouveaux elements de soutènement de la mine, en contribuant pour la minimisation de ses coûts de stabilisation, avec la manutention de sa securite, Parce qu'il est possible d'appliquer cette methode à d' autres types d' excavations, cel1e-ci est decrite et illustree en detail.

ZUSAMMENFASSUNG:

Felsbauprojekte, die aufeinanderfolgende Entscheidungen ueber den Ausbautyp und -anzahl erfordern, der benötigt wird, um Hohlraume stabil zu erhalten, verlangen ein verlassliches Verhaltensmodell, um jene Entscheidungen zu begruenden. Im Kohlebergwerk Germunde (Portugal) wurde die vorlaufige Ausbauauswahl fur eine neue Teufe durch die Analyse der zahlreichen Ergebnisse von in zwei vorherigen Bergwerksteufen erhaltenen Konvergenzmessungen möglich gemacht. Eine enge Korrelation wurde zwischen 3 Variabeln gefunden: die Durchschnittskonvergenzgeschwindigkeit der Strecken (die ihre Stabilitatskriterien darstellen), die Gebirgsklassen der durch die Hohlraume angeschnittenen Formationen, und die Ausbauentwurf and - auswahl entwickelt, die auf die nachfolgenden Bergwerkstatigkeiten angewandt wurde, und so zur Ausbaukostenminimisierung mit einer gleichzeitigen Sicherheitsgewahr beitrug. Wegen der möglichen Anwendbarkeit der Methode auf andere Situationen, wird sie beschrieben und detailliert erlèutert

1. INTRODUCTION

Design, selection and installation of supports for underground excavations are not always reliable engineering processes, which are established with appropriate knowledge of all influencing variables, plus using the right mathematical models to define support dimensions and finally choosing the least objectionable compromises among the economy and the safety of the alternative solutions for each problem. In general many insufficiencies occur in field operations: there are imperfect information on the rock mass conditions and properties, no reliable models for design are available, the labour force and existing equipment preclude the selection of certain support types and sometimes not enough importance is ascribed to the economic aspects of the problem. Practical constraints require that most support materials are acquired in advance of observing real cavity performance, and selected on the basis of preexisting hypothesis about excavation behaviour, sometimes established before the actual opening has been created. In many other situations this selection process is accomplished by analogy with similar types of supported cavities, regardless of the safety factors or economic consequences that those examples contain.

This content is only available via PDF.
You can access this article if you purchase or spend a download.