An approach to mine design incorporating several new ideas and numerical approaches is presented.
Es wird ein Ansatz fuer den Entwurf von Minen prasentiert, der mehrere neue Ideen und numerische Ansatze beinhaltet.
Un point de depart pour le projet de mines comprenant plusieurs idees et approches numeriques est presente.
Mine design, in salt, potash, or any material, must be a continual optimisation effort during the mine life. Optimisation requires repeated iteration of a design procedure, which consists of the following activities: a) Assessment of rock conditions and geological state; b) Choice of mine geometry and changes to be implemented; c) Determining the mechanical behaviour of relevant materials; d) Choice and application of methods of analysis; and, e) Monitoring to verify behaviour and monitor safety. The first issue, initial state, is the purview of geologists who provide geological models, which become more refined through time, to the rock engineer. This may include information on mineralogy, clay seams, water-bearing strata, fracturing of overburden, and in situ stresses. The second issue, mine geometry and evolution, is often dictated by the mining approach and the ore body, with goals of high extraction ratio, short transportation distance, high safety, and low costs. The third issue, material behaviour for the strata encountered, evolves as refinements in understanding material response are achieved in the laboratory and in the field, where room behaviour helps perfect models (Rothenburg et a1.,1991), and as more data on material distribution is collected. Analysis method is the fourth category; analysis may be empirical, analytical, statistical, numerical, or a combination of several approaches. Finally, confirmation by monitoring is an essential aspect of dynamic optimisation, providing feed-back to the rock engineer, a means to refine the design, explanations for difficulties encountered, and providing performance data for personnel safety purposes. With private and public cooperation, some developments that help mine design in salt rocks have been developed (CANMET, 1987, 1990). These are described qualitatively; detailed descriptions must be pursued elsewhere. We deal with salt and potash mines with tabular extraction at dips no larger than 12–13°, and thicknesses that may be constant for kilometres or may vary from 1–12 m over distances of 1000 m. Water-bearing strata usually exist some distance above the mining horizon, therefore long wall techniques permitting back collapse cannot be used, and roof integrity is vital. Steeply dipping seam cut-and-full methods are rare in potash, and will not be discussed further, although our methods are equally applicable to these cases. Tabular room-and-pillar methods are dealt with; rooms and pillars are understood to be long, perhaps a kilometre or more, compared to their widths, typically 10–25 m for rooms, 20–40 m for pillars.
Geological structure dictates mining method and layout (Barr, 1977). Figure 1 is a typical ore body in Saskatchewan, Canada; Figure 2 an ore body in New Brunswick, Canada; and, Figure 3 is a schematic of a salt dome being exploited. All these approaches use room-and-pillar geometry. Initial conditions such as depth (stress), structural geology, temperature, moisture content, and mineral distribution govern materials testing approaches and may affect numerical modelling strategy. These factors, with the mine design itself, govern mechanical mine behaviour in potash mining, mineralogical analysis can help design by delineating areas of different properties. If carnallite content variations are known, room and pillar geometry can be altered to satisfy local conditions.
