Underground Mine Workings Convergence Dependence on Operation Time and Location Depth

The article deals with subsurface location depth as one of the most important technical and mining factors in providing safe stability levels for any underground mine working. With increasing depth, takes place a change of mechanical properties of rocks, their transition into a boundary state, which has a special value and influence in relation to the long-term stability of the mine workings, both vertical and horizontal, in the sense that the mining pressure manifests itself differently and there is the problem of choosing the right support solution; also, it is enhanced the natural and secondary stress state and convergences became strong functions of depth. Based on the results obtained in the laboratory tests and in situ measurements and observations, carried out at several collieries within the Jiu Valley coal basin, in this article is settled the variation law of rocks surrounding mine workings depending on the depth of mining works and time lapse. The article also presents the development of a method for determining critical depth, parameter considered as depth wherefrom the plastic flow of rocks start to occur.