ABSTRACT:

The application of risk assessment and management techniques to the design and construction of underground excavations is examined and a comprehensive approach proposed. The approach is based on experience from other industries, the authors own research and practice and case examples from other branches of geomechanics. A summary of current risk assessment practice in underground excavation is provided, based on questionnaire responses. The differences in approach for underground excavation and other applications are detailed. In underground excavations the main design uncertainties are location and scale of weaknesses in the rock mass which require special treatment within standard risk assessment methods. There is a natural progression from risk based design to the observational method during construction in most underground excavation applications.

RÉSUMÉ:

L' application d' evaluation de risques et de techniques de gestion à la conception et construction des excavations souterraines est examinee et une approche complète est donnee. Cette approche est basee sur es experiences provenant d' autres industries, sur la propre recherche et la pratique des auteurs de cet article et surdes exemples de cas d'autres branches de geomecanique, Une recapitulation de la pratique actuelle de I' evaluation de risques dans les excavations souterraines est faite à partir des reponses d' un questionnaire. Les differences d' approches pour une excavation souterraine et pour d' autres applications sont detaillees. Les principales incertitudes de conception dans les excavations souterraines sont I' emplacement et I' echelle de faiblesse de la masse rocheuse qui necessite des soins particuliers lorsque les methodes standards d' evaluation de risques sont utilisees, 11 y a une progression naturelle de la conception basee sur Ie risque à la methode d' observation durant la construction dans la plupart des applications d'excavations souterraines.

ZUSAMMENFASSUNG:

Die Anwendung von Risikobewrtungs- und -managementtechniken auf Entwurf und Bau Von unterirdischen Ausgrabungen wird untersucht und ein umfassendes Verfahren vorgeschlagen. Das Verfahren beruht auf Erfahrungen aus anderen Gewerbezweigen, auf eigener Forschung und Praxis, sowie Fallbeispielen aus anderen Bereichen der Geomechanik. Eine Übersicht ueber die derzeitig gangigen Risikobewertungspraktiken in Ausgrabungen unter Tage, die auf Antworten zu Fragebögen beruht, wird Vorgestellt. Dhie Unterschiede fuer duennterVirderisfachhreen Aufusrgraubnutenrgirednischseind AduiesgHraabuupntguennsichuenrhdeitaennderebneimAnwEnetnwduurnfgednie Lage und das Ausmass von Schwachstellen in der Gesteinsmasse, die im Rahmen von normalen Risikobewertungsmethoden eine besondere Behandlung erfordern. Es gibt eine natuerliche Abstufung vom auf risiko basierten Entwurf zu der auf Beobachtungen gegruendeten Methode wahrend dem Bau in den meisten Ausgrabungen und Ausschachtungen.

1 INTRODUCTION

There is an increasing interest and usage of risk assessment methods in geotechnical engineering applications and this paper addresses, more specifically, underground excavations in rock. Many of the techniques were developed in other industries such as aerospace, petrochemicals and power generation. Of particular relevance to geotechnics are the methods used in assessing potential radioactive waste disposal sites and radionuclide migration within groundwater. There has been considerable development within the areas of slope stability assessment and in toxic waste disposal and landfill (leachate leakage). In the UK the interest in risk assessment has been driven by several important initiatives by the Health and Safety Executive, the Royal Society (1992) and the Engineering Council (1992). Many codes of practice in UK, the EC and elsewhere now incorporate risk assessment, but it is not well developed in the context of underground excavation. Another positive development is the ready availability of powerful computing tools for risk assessment, including simulation, in accessible spreadsheet based packages. There is confusion about the meaning of the terms risk assessment, risk evaluation, risk management etc. and it is considered useful to clarify this, in the context of underground excavation, mainly through the presentation of examples. It is necessary to develop a practical approach where the techniques can be readily understood and applied at the appropriate time. In a project at the Camborne School of Mines, funded by the UK Engineering and Physical Sciences Research Council (EPSRC), we are undertaking the task of determining the realistic limits and optimum application of risk assessment methods to underground excavation projects, mainly with a geomechanics perspective, but including financial considerations.

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