ABSTRACT:

In rock dynamics, stress wave propagation and dynamic fracturing are important transient phenomena governing the stability and safety of geotechnical structures. In this work combined experimental and theoretical approaches are developed to study various aspects of the dynamic behaviour of rock, and specifically address stress wave interactions with rock mass discontinuities and dynamic fracturing due to blasting. The main topics dealt with are:

  • wave interactions with rock joints,

  • wave interactions with excavations, and

  • blast induced fracturing.

The paper presents new results of theoretical investigations, numerical simulations and experimental model tests, which lead to an improved understanding and perspective of the complex phenomena of rock dynamics in terms of stress wave and fracture propagation. The ultimate implications of this work are improved safety and efficacy of geotechnical operations, such as, for example, deep-level mining.

RÉSUMÉR:

n dynamique de roches, les ondes de chocs et la dynamique de fissures sont un important phenomène dynamique gouvemant la stabilite et la securite de structures geotechniques. Dans ce travail, les approaches combinees experimental et theorique sont developees pour etudier les divers aspects du comportement dynamique de la roche, et met au point les interactions entre les ondes de chocs avec la discontinuite de la masse de roches et la dynamique de fissures resultant du minage,

ZUSAMMENFASSUNG:

Stabilitat und Sicherheit im Bergbau wird wesentlich von dynamische Vorgangen beinfluβt. Wichtige dynamische Vorgange sind elastische Wellen und schnell laufende Risse. Diese Dissertation zeigt die Entwicklung der Kombination von experimentellen und theoretischen Methoden zur Untersuchung der unterschiedlichsten Aspekte des dynamischen Verhaltens von Fels. Insbesondere wird die Wechselwirkungen von elastischen Wellen mit Fels-Diskontinuitaten und mit durch Sprengarbeiten induzierten, rasch laufenden Rissen untersucht. Ein wichtiger Teil der Forschung ist die Verifikation der numerischen und analytischen Resultate durch Vergleiche mit Laborversuchen unter kontrollierten Bedingungen.

1
INTRODUCTION

Rock dynamics deals with transient processes such as stress wave and fracture propagation, and the interactions thereof, and the stability and integrity of rock loaded dynamically. Within the mining context, research in this field has been spurred in the last three decades particularly by the technical difficulties of deep-level mining operations and the associated occurrence of seismicity and rockbursts. Although the research effort has accelerated over the past decade, these dynamic events continue to account for the largest single cause contributing towards the toll of injuries and fatalities suffered by the workforce during mining operations. The aim of this thesis is to conduct new and practically relevant work to gain further knowledge of rock dynamics. The work addresses stress wave propagation and the interaction with discontinuities, as well as dynamic fracturing due to stress wave loading and blasting. More specifically, the main objectives can be classified according to the following categories, which are illustrated for a deep-level mining application in Figure 1 a). A photograph of a typical stope in a deep-level gold mine is given in Figure 1 b).

  • Stress Wave Interactions with Rock Mass Discontinuities: Various types of rock joints and fractures, and the associated interface conditions, are analysed and their stress wave reflection and transmission characteristics are quantified.

  • Stress Wave Interactions with Tabular Mining Excavations: The transient wave field due to wave interactions with mine excavations is investigated, and the mechanisms of energy channeling and fracturing due to the superposition of reflected, refracted and diffracted waves are studied.

  • Blasting: The process of rock blasting is examined, where consideration is given to (i) blast induced stress waves and their proclivity for promoting fracturing in the borehole vicinity, and (ii) fractures driven by combustion gases. The findings are based on analytical and numerical, as well as experimental investigations. A recurring theme throughout this work is the verification of numerical and analytical results by means of controlled laboratory experiments. This is considered an important aspect of the investigation and ensures accurate, relevant and meaningful results.

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