ABSTRACT
When forecasting the increase with time of the earth surface subsidence resulting from deforming of interchamber pillars left during mining rock salt and potash ores, one may be interested in such characteristics of these pillars as: modulus of reduction in their response capability; their minimum remaining strength; modulus of increase in the pillars’ response after the start of the massif consolidation (this massif formed from these pillars by the time of reducing their remaining strength down to a minimum value) and other characteristics. Modulus of reduction may be used, moreover, for evaluating the capability of salt-bearing interchamber pillars, being in the “beyond-limit” state, to brittle failure. Under the term “beyond-limit” state in this case is defined as the state (or condition) of a rock after its loading until the ultimate strength or after its deformation reaches an ultimate value.
Laboratory investigations have been carried out to evaluate the relationship of the above named characteristics and conditions for deforming of interchamber pillars, using as an example various kinds of sylvinite ore and rock salt being mined at the Upperkama potash ore deposit. In the process of the investigation the following conditions were varied: height-to-diameter ratio of test samples; rate of sample deformation after deformations (strains) reach beyond-the-limit values; values of beyond-the-limit deformations after which the samples were deformed at various rates; dimensions of the space surrounding the samples under testing (into this space the samples could deform as pillars into the rooms). The results of these studies have led to conclusions that are of important practical interest.
