Mine design may often be conservative when it comes to room width and the number and size of pillars. A favourable magnitude of the horizontal in-locked rock stresses makes the roof more stable and many pillars are therefore needless. The factor of extraction and the mine economy may be considerably improved through field and laboratory measurements. Favourable horizontal stresses may lead to considerable mine lay-out changes. The horizontal stresses can be measured by overcoring techniques. SINTEF normally recommend three dimensional rock stress measurements in the very early phase of the mining to recommend optimal geometry. Recommendations are primarily based on numerical modelling and practical mine design experience. A second rock stress measurement is usually performed when the mining has started at the first level. Thesemeasurements are performed in pillars and roofs. A considerably difference of the rock stresses obtained from the numerical modelling may lead to changes in the mine design. Further control measurements are usuallyperformed when entering into new rock conditions or a new level.
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