Method for ensuring geomechanical safety during undermining of water-protective strata

Introduction. This paper addresses the issues of geomechanical safety during the extraction of potash-magnesium salts at the Palasher site of the Verkhnekamsk potassium-magnesium salt deposit. Special attention is given to the analysis of the stress-train state (STS) of the water-protective stratum (WPS) under undermining conditions. The applied numerical methods make it possible to predict the behavior of the rock mass and determine the conditions for crack formation that may compromise the integrity of the WPS. Purpose of the research. The purpose of the study is to develop a method for forecasting the STS of the WPS, taking into account its deformation characteristics, the regularities of crack formation, and their development. The aim is to determine the limiting conditions under which a hydraulically connected crack system forms, which is critical for preventing water inflow into the mined-out area. Materials and Methods. A modified viscoelastic-plastic model of sylvinite deformation with the Drucker–Prager plasticity criterion was used in the calculations. The Concrete Damaged Plasticity model ensures the simulation of brittle failure in the rocks composing the WPS. The parametric support for the models was based on laboratory testing of rock samples and the results of instrumental monitoring of deformation in interchamber pillars at the deposit. Results. A forecasting method for the STS of the WPS has been developed based on a viscoelastic-plastic deformation model of interchamber pillars in the salt stratum and the brittle failure behavior of WPS rocks. The model ensures the accumulation of damage in the WPS, accounting for long-term predicted vertical displacements along its base. The analysis of STS modeling results for the WPS at the Palasher site of the Verkhnekamsk potassium-magnesium salt deposit revealed regularities in the formation of a hydraulically connected crack system. A comparative analysis of the SSS in the WPS with varying thicknesses established the relationships between the initiation of a primary crack in its roof and the development of a hydraulically connected crack system. Resume. The study focuses on analyzing geomechanical processes during the undermining of the WPS at the Verkhnekamsk potassium-magnesium salt deposit. The developed numerical modeling method allows predicting changes in the STS of the WPS and identifying the conditions under which critical rock failure occurs. This enables the implementation of preventive measures to ensure geomechanical safety during WPS undermining at similar deposits. Regularities of crack formation and critical conditions of WPS failure have been established.