Complex estimation of geotechnical risks in mine and underground construction

Introduction. Projects for the construction of underground structures and mines often involve significant geotechnical risks. The uncertainty associated with geotechnical conditions implies the development of a specific approach to making design and constructive decisions. Even after a thorough geotechnical study, the ability to accurately predict the behavior of adjacent rock massif is often difficult due to the large number of engineering-geological and hydro-geological variables. Most of the identified risks can be eliminated at the design stage. Residual risks should be subjected to a comprehensive assessment, including qualitative and quantitative analysis and calculations of damage from potential risk and technical and economic efficiency of the adopted design decision. Objective. Complex estimation of geotechnical risks in mine and underground construction based on the analysis of indicators of the implementation of accidents by mining-geological and mining-technical factors, taking into account the use of special methods of construction. Methodology. A сomplex estimation of geotechnical risks was carried out on the basis of the theory of emergency risk using methods of mathematical statistics, probability theory; the method of expert assessments to obtain the values of vulnerability coefficients of the applied technologies of mine and underground construction. The developed methodology includes several stages. At the first stage of a сomplex risk estimation, it is necessary to rank the geotechnical risk factors selected for analysis, for which a concordance coefficient is introduced. When analyzing each of the emerging geotechnical figures during the construction of a specific underground or mine construction facility, one of the defining indicators is the numerical expression of the potential damage from the occurrence of an emergency situation, which represents the percentage ratio of the excess of the construction period in real practice to the same indicator laid down in the project, or the ratio of the increase in the cost of construction to the estimated cost. Next, the numerical value of each type of risk is determined and a scale of numerical values of risks is compiled, on the basis of which decisions are made on the management of each specific risk. At the end, the vulnerability of a mine or underground construction facility under construction is determined, i.e. the degree of its possible damage and destruction when exposed to abnormal situations of a natural and man-made nature. Results and discussion. A methodology has been developed for the сomplex estimation of geotechnical risk in mine and underground construction based on the ranking of risks according to the degree of vulnerability of the technologies used. Ranking of construction objects by their vulnerability to various impacts allows us to assess the correlation between the values of the parameters and the qualitative characteristics of the elements of the “mining – rock mass – construction technology” system and the factors that lead to the development of potential damage. In the course of the research, a generalized indicator of the predicted geotechnical risk was identified, which allows taking into account the impact of construction methods on the risk. Since mine workings are currently being built mainly in complex hydro-geological and engineering-geological conditions, the calculation of the generalized indicator focuses on the use of special construction methods, which required the introduction of correction factors to calculate the indicator of the predicted geotechnical risk. The values of correction coefficients for the most used special methods were obtained by the method of expert assessments. Conclusions. One of the important aspects of a сomplex estimation of geotechnical risks in mine and underground construction is to determine the vulnerability of the “mining - rock mass – technology” system. Vulnerability depends on the location of the mine, its cross-section, engineering-geological and hydro-geological conditions, mode of operation, reliability of load-bearing and fencing, etc. By the method of сomplex estimation, vulnerability coefficients of underground structures under construction and mine workings were obtained, as well as correction coefficients taking into account the construction method.