Geomechanical risks at underground gypsum mining

Abstract

In the focus of the article is estimation of geomechanical risks during exploitation of gypsum mines. Underground extraction of gypsum is performed mainly with the use of room-and-pillar system of mining. This method provides long-term exploitation of large mine workings. The maintenance of workings in operation condition for decades is associated with existence of geomechanical risks. They potentially reduce stability of the mine workings. This negatively affects safety of personnel being underground. The long-term consequences are related to the deterioration of the ecological state of the environment. The main geomechanical processes that cause risks in the operation of gypsum mine workings are identified in the publication. Gypsum mine differs by supports installed only in a few sectors. In these conditions, the most dangerous are formation of the block structure of rock mass and stratification of the roof. Uncontrolled development of these processes can cause an emergency situation. Evolution of karst formation above the mine workings can cause caves on the day surface. Great water inflows are also a significant threat. The cases are known when separate sections in the mine field and entire mines were flooded . An approximate gradation of negative consequences as a result of the influence of each geomechanical process is presented. It is shown that a significant factor for the occurrence of geomechanical risks is the changed physical and mechanical properties of the rock mass. In this case, simulation can be used in order to quantify geomechanical risk. Its application for estimating risk of roof falls with known variation of calculated parameters is shown. The result of the simulation is the curve of probability distribution of safety factors of roof. The probability of unacceptable parameter values is calculated. The possible consequences of a gradual decrease of safety factor are taken into account. A quantitative estimate of the magnitude of geomechanical risk for a concrete project was obtained. This methodology is universal. It can be used to assess operational reliability of engineering objects under significant impact of unstable factors of natural origin. Keywords: geomechanical process, geomechanical risk, gypsum mine, safety factor, simulation.