ABSTRACT
This paper describes the research carried out to examine the geotechnical design characteristics of the sandstone aquifers in the Collie Coal Basin under conciliions anticipated during dewatering operations.
The Collie Coalfield has a long history of strata control problems. They manifest themselves in the form oi localised poor roof control, surface subsidence, slope instability and mine abandonment (due to sand-slurry inrush). A major source of these problems is the very extensive system of weak, saturated, sandstone aquifers. As a result, past underground operations had been limited to room and pillar extraction achieving 30–40 percent recovery. The trial introduction of the Wongowilli method of short-wall extraction, increasing recovery to 60–70 percent, required an enhanced understanding of strata mechanics to enable confident application of engineering design.
The methodology adopted consisted of simulation of the assumed insitu conditions on triaxially confined, saturated laboratory specimens prepared from insitu core samples. Dewatering was simulated by pore pressure release followed by vertical water flow induction through the specimen. Any deterioration of the specimen and the associated volume change was monitored. The triaxial tests results were related to the texture, bulk properties, strength and deformability, permeability and wave propagation properties. These properties were used to indicate the risk of potential failure under given stress conditions.
This paper contains description of the equipment commissioned, test techniques, results, analysis and interpretation of the data obtained.
