Natural study of marginal array rock`s stress state

Safety working out water-soluble ore fields in many ways depends on the stability of chamber development system`s elements. To monitor the interchamber pillars` status a method of experimental and theoretical evaluation of the geomechanical processes taking place in the array was developed, the essence of which lies in the meaningful results interpretation of mechanical characteristics and the stress state experimental studies of load-carrying structures by mathematical modeling methods. The article describes the method of estimating the marginal rock array`s stress state. The tension control was made using an acoustic memory effect. The measurements were performed in the wells with the help of a Goodman hydraulic jack. Its feature is the ability to create a load on the borehole array in the same plane, that allows to evaluate the stress magnitude in various directions. During the loading of the measuring borehole walls there is a discontinuous increase in the activity of acoustic emission. The pressure, which is logged in the hydraulic system, was taken at the level of the natural stresses acting in the marginal array. As a result of complex laboratory and field studies methodological features of stress analysis were identified using memory effects in salt rocks of the Verkhnekamskoye potash salt deposit. The experimental data analysis showed that in the “fresh” interchamber pillars a bearing pressure maximum is located near the contour of exposure and in 1.8-2.0 times higher than the load of of the overlying rocks` weight (gH). In the central part of the pillar the vertical stress level is 1.25-1.4 gH. With the increase in pillars` service life the marginal array`s stresses magnitude declines to the stress level of the overlying rocks weight. The horizontal stress increases with moving from the pillar contour and are approximately 60-70% of the vertical. These instrumental measurements results are a source data for assessing the long-term sustainability of interchamber pillars in sylvinite layers mining