From flooded mine workings the regulated descent of water with a large hydrostatic head can be ensured at reliable determination of the size of the target left between the flooded mine workings and the face of the slipway, through which the water is planned to be discharged. To calculate the size of the pillar it is necessary to know the compressive strength of rocks, which is usually determined by samples at natural moisture.

The zone of inelastic deformations resulting from mining operations, as is known, is characterized in most cases by cracking, developing in time. On the other hand, after a certain period of time, the fracturing of rocks may decrease due to their compaction, i.e. closure of cracks.