Abstract
Cave mining progresses to depths exceeding 1000 m and ore bodies situated in competent and strong rock masses are nowadays extracted by different cave mining methods. Widely applied caving methods in massive deposits are block and panel caving, inclined caving, and sublevel caving. All caving methods have in common that rock mass caves during extraction of an ore body in a controlled way. As a result, regional stress changes occur, considerable abutment stresses form, and large-scale subsidence and significant seismic energy releases occur. Experience shows that these rock mechanics effects become especially critical at great depths, where primary stress magnitudes reach and exceed rock mass strength, as well as in strong competent rock masses, which require large footprints to enable continuous caving. The presented raise caving method addresses previously mentioned rock mechanics issues. Initially, de-stressing slots are developed from raises with a minimum amount of pre-development. Substantial pillars separate neighboring slots in order to control stress magnitudes and seismicity near slots. The slots provide a stress shadow for production infrastructure so that large-scale mineral extraction can take place in de-stressed ground. As mining progresses, pillars are extracted and hanging wall is allowed to cave. Results of a pre-study conducted together with LKAB have highlighted advantages of raise caving from a rock mechanics, safety, and cost point of view.
Highlights
Caving methods in massive deposits rely on naturally induced rock mass failure either by means of gravity, prevailing stresses, or a combination of both
Starting in the late 1990s, cave mining progressed to greater depths and more competent rock masses, for example Northparkes mine, Cadia mine, or Kiruna mine
Stopes are blasted from production raises, which are developed in de-stressed rock mass, and the swell is drawn at draw points
Summary
Caving methods in massive deposits rely on naturally induced rock mass failure either by means of gravity, prevailing stresses, or a combination of both. A simple rock mechanical model illustrating critical points in currently applied caving methods in massive ore bodies is a tabular slot. Such a tabular slot provides an overview of the stress distribution around an undercut in block and panel caving before continuous caving is initiated and around active sublevels in sublevel caving. The high abutment stress magnitudes are critical and can damage the undercut and production infrastructure, adversely affect rock mass properties in the future production level, or trigger damaging seismic events. The slot model loses its validity in block and panel caving in areas where caving has been initiated and has propagated, the abutment stress issue during undercutting is inherent.
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