Difficult mining conditions are commonly experienced during underground roadway driveage in the Southern Coalfield, Australia. Rock failure occurring in roof strata at the mining face is commonly experienced together with high loading of roof support and reinforcement. The type of rock failure surrounding a mine roadway and the subsequent opening stability are significantly influenced by the orientation of the face with respect to the in-situ principal stresses. Mine layouts and roof reinforcement procedures have been developed on the basis of an anticipated mode and geometry of rock failure occurring at or ahead of the mining face.


Les conditions difficiles minieres sont rencontre pendant tracage des voies souterraines dans la region sud du Bassin Houiller de Sydney en Australie. L''occurrence de cassure des roches dans les strates du toit au chantier minier est rencontre ordinairement avec les charges lourds du soutenement et renforcement du toit. Le type de cassure de roches environnant une voie miniere et la stabilite suivante du chantier sont influence significativement par les directions comparatifs de la orientation de la face et les pressions principales de terrain in situ. Les plans des mines et les procededes de renforcement du toit ont ete developpe Sur la base d''une mode et d''une geometrie anticipee de cassure de roche qui se presente a ou en avant de la face miniere.


Schwierige Bergbau umstande sind oft aus Erfahrung entstanden wahrend des abbaus untertag strecken vortrieb in den Sudlichen Kohlfedern in Australien. Die erfahrung hat ergeben das das hohe gewicht der geschteinsmassen so schwer ist, das gesteinsrisse vorkommen in den gesteinschichten beim Abbaustoss, zusammen mit hohe beanspruchung der Abstutzungen und verstarkungen. Die art des Gesteinsbruch in der umgebung der Vortriebstrecke sind die folgen der offnung stabilitat hat ein bedeutenden einfluss auf die orientierung von dem Abbaustoss mit hinsicht auf die haupt spannungen (stress). Grubenauschnitt und Deckenverstarkungen verfahren, sind so Konstruiert Worden wegen dem vorrausschende quantitative mineralogische zusammensetzung und das geometrie des Gesteinsbruch.


Underground coal mining is being undertaken at increasing depth and within highly stressed rock masses. Mining developments are subject to the effects of virgin stressfields and gross stress redistributions occurring about extraction panels. Many coal measure rocks are weak engineering materials which require artificial support or reinforcement to maintain opening stability. High production mining operations require rapid and stable roadway development with minimum obstruction. The magnitude and orientation of stresses are major factors influencing underground roadway stability in mining areas within weak strata and high virgin stressfields (Gale et al., 1984, Gale and Blackwood, in press). This paper presents an overview of the application of stressfield data to the optimisation of roadway driveage in the Bulli coal of the Illawarra coal measures, N.S.W., Australia.


The Illawarra coal measures are located in the southern portion of the Sydney Basin, a broad basin structure containing extensive coal reserves Permian Age (Fig. 1). The coal measure strata are gently dipping between 0- 50. Dominant structural features within the coal measures are broad folds, minor monoclinal flexures and normal faults with displacements up to 100 m. Igneous dykes, sills and volcanic plugs intersect the coal measures. The stratigraphy and structure of the coal measures has been discussed in greater detail by Bunny (1972) and Wilson (1975). The Bulli Seam is the upper seam of the coal measures and is enclosed by roof and floor sections of siltstone, sandstone, mudstone and shales. Finely interbedded sequences of these rock types are referred to as laminite, and commonly occur in the immediate mine roof section.


Stress measurements conducted in the coal measures, and the Sydney Basin in general (Enever et aI, 1980, Walton, 1983; Gale, 1983; Gale et al., 1984 (a), and 1984 (b)) delineate the existence of high and anisotropic lateral stress components. In situ stress measurements have been made at 13 sites in the Southern Sydney Basin using the CSIRO HI stress cell and the overcore technique (Worotniki and Walton, 1976). Stress measurements were made at distances of 6.5 – 12.5 m from development roadways in collieries and represent the virgin stress environment into which roadways are driven. Results from the in situ stress measurements indicated that the maximum principal stress, 01'' was effectively horizontal and that the virgin stressfields were often oriented with respect to local and regional structural features. The in situ stresses measured in the coal measures are consistent with near surface stress measurements reported elsewhere (Hoek and Brown, 1980) for which horizontal stress components exceed vertical stress components.


The effect of virgin stress distributions on roof behaviour is a complex function dependent upon the strength and stiffness of the strata, the magnitude of the principal stresses, the distribution of discontinuities and the orientation of the roadway.

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