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Study and Enhancement of Underground Mining Technologies to Prevent Earth’s Surface Failures

Study and Enhancement of Underground Mining Technologies to Prevent Earth’s Surface Failures Revista Minelor – Mining Revue ISSN-L 1220-2053 / ISSN 2247-8590 vol. 28, issue 1 / 2022, pp. 42-49 STUDY AND ENHANCEMENT OF UNDERGROUND MINING TECHNOLOGIES TO PREVENT EARTH'S SURFACE FAILURES 1 2 3 4 Mykola STUPNIK , Olena KALINICHENKO , Mykhailo FEDKO , Mykhailo HRYSHCENKO , 5 6* 7 Vsevolod KALINICHENKO , Serhii CHUKHAREV , Sofiia YAKOVLEVA , Alexey POCHTAREV Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine LAMET s.r.o., Bellova 3, 04001 Košice office: Rozvojovά 2 A, Slovakia DOI: 10.2478/minrv-2022-0004 Abstract: The work contains studies of the problem of stabilizing geodynamic processes in the rock massif, preservation of the daylight surface and ecological balance in the mined-out and operating mine fields of Ukraine. The main regularities of influence of sublevel-room mining systems with backfilling on changes of the stress-strain state of the rock massif and the main structural elements of the block are determined. Rich iron ore mining by underground methods and subsequent transition to the sublevel-room mining system with backfilling is modeled. New technologies for mining ore deposits are developed and current ones are enhanced to prevent the earth’s surface failures, stabilize landslide and displacement zones within the boundaries existing at the time of transition to systems with backfilling. The developed resource-saving technologies of mining can significantly enhance ore extraction indicators and the environmental condition of the basin by locating waste dumps and disposing wastes of mining enterprises in the mined-out area of underground mines. Keywords: underground mining, stress-strain state, rich iron ores, magnetite quartzite, ore drawing, flowsheet 1. Introduction Mining deposits by underground methods results in formation of significant undermined areas. As a rule, the main characteristic of these areas is the disturbed daylight surface with terraced zones and sometimes subsidence that endanger human production and civil activities. Currently, in Ukraine and worldwide, influence of underground mining on the daylight surface stability is insufficiently studied. Existing studies are usually region-related. In our opinion, it is necessary to develop new integrated technologies that allow conducting high-efficiency underground mining with simultaneous disposal of mining wastes in mined-out areas of underground mines and preservation of the daylight surface and existing urban structures. Therefore, the study of regularities of stabilization of geodynamic processes in the rock massif and development of resource-saving technologies for mining various grade iron ores and development of technological solutions to prevent subsidence of the earth’s surface in iron ore underground mining is an urgent scientific and technical problem of significant scientific, environmental and practical and technological importance. Corresponding author: Serhii Chukharev, Kryvyi Rih National University, Kryvyi Rih, Ukraine, contact details (e-mail:konf.knu@gmail.com) 42 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 2. Analysis of the problem of preserving the daylight surface in mined-out and operating mine fields of Ukraine Extraction of significant volumes of minerals changes the stress-strain state of rocks, which in turn affects the processes of rock massif displacement when it can reach the earth’s surface and destruct industrial and civil objects located in this area. Extraction of salt in Kalush mining district (1867 - 2007) by underground mines Kalush and Novo-Holyn is an example of the situation of this kind. Technogenic activities caused a threat of a trans-boundary water- environmental emergency (WES) in Dniester river basin and were hazardous to human health and safety. The resulted strain of the earth’s surface over underground mining stopes of about 17 M m causes significant subsidence of the earth’s surface with brine displacement, formation of salt lakes and sudden sinkholes, with damage to and destruction of buildings and structures in Kalush and nearby villages. The first subsidence on the earth’s surface in Kalush occurred in the summer of 1987 on Parkhomenko (now Vitovskyi) Street (Fig. 1). The depth of the sinkhole was up to 8.5 meters. Nearly two dozen homes were under threat. In 2008, another sinkhole occurred in the same neighborhood and in the autumn of 2015 – another one only a few meters away from the old one. Subsequently, these sinkholes combined. Figure 1. The first subsidence in Kalush At present, the daylight surface subsidence within the mine area varies from 0.5 m to 5.1 m, the forecast values reach up to 7.1-9.1 m, which under activated karstification significantly aggravates the engineering and geological conditions of Kalush basin. Kryvyi Rih iron ore basin faces similar problems. Relevance of geo-mechanical researches is so significant that they are conducted at almost all large mining enterprises. Moreover, there have been made numerous attempts to summarize the results of the researches and present them in the form of separate general regularities. However, in general, these studies are, as a rule, region-related. Thus, on 13 June, 2010, at Ordzhonikidze underground mine, immediately after the planned blasting operations, there occurred intensive daylight surface failure in the mine allotment zone within survey axes (- 37)–(45). The total area of the failure made 16.5 ha (Fig. 2). 43 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 Figure 2. Daylight surface failure in the Ordzhonikidze mine allotment zone On 17 August, 2010, in the Tsentralno-Miskyi district of Kryvyi Rih (5, Urytskyi Street) a partial failure of the earth’s surface between 3 am – 6 am resulted in a crater within survey axes 57–58 and the average strike line (ASL) from +30 to +50 (Fig. 3). The failure is located in the mine field of the HPU mine (closed down in 1972) and above the mine workings resulted from iron ore mining. The topographic survey performed by the specialists of the State Enterprise “DPI “Kryvbasproekt” showed that the diameter of the crater reached 18 m, and its volume made 1500-1600 m , i.e. nearly 1700- 1800 m of underground voids was filled due to failure. Fig. 3 presents the failed area of the daylight surface in the mining allotment zone of the HPU mine that was closed in 1972. Figure 3. The failed area of the daylight surface in the mining allotment zone of the HPU mine Unfortunately, such phenomena are not sporadic for Kryvyi Rih iron ore basin. One of the main conclusions drawn from the given data can be expressed as follows: today's expenditures for implementing measures to prevent possible emergencies are much lower than the future costs of eliminating consequences of such definitely possible situations. One of the ways to prevent emergencies on the daylight surface within mining allotments of Kryvyi Rih basin underground mines consists in applying technologies of underground mining with the subsequent backfilling of the mined-out areas. 44 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 3. Research methods The criterion for the study and enhancement of underground mining technologies that prevent formation of sinkholes is selection of the optimal concept of research of the stress-strain state of the rock massif and daylight surface failures during ore mining operations that cause significant mined-out areas. Currently, a significant number of analytical methods and computer programs are used to calculate and model distribution of stresses in the rock massif around the mined-out area. Classical modeling by the finite elements method is the most common [4, 7, 9, 12, and 13]. In general, based on results of modeling by the method of finite elements, it is affirmed that when stresses in certain areas of the massif exceed permissible ones, the rock massif begins failing. To study and enhance the underground mining technologies that prevent failures of the earth’s surface, the following application programs enabling determination of the stress-strain state of the rock massif are used: “SolidWorks”, “Lira”, “Ansys”, “GTSNX”, “SCAD”, etc. Such programs help study strains of the rock massif both on mined-out ore deposit levels and the daylight surface. In the course of the research, the finite elements method and the ANSYS 2021 software complex are used to solve the problems related to determining the geodynamic state of the rock massif, fields of stresses and calculating strains of the rock massif around the mined-out area and on the daylight surface [1–3, 5, 6, 8, 10, and 11]. Table 1 presents the initial physical and mechanical properties of the rock and the backfilling material used when calculating stresses and strains. Table 1. Physical and mechanical properties of the rock and the backfilling material Ore Rock Backfill Unit of Caved Parameter 1Р 2Р 3Р 4Р П measurement rocks f=3-5 f=4-6 f=5-7 f=6-8 f=5-7 Young's MPa 22000 25000 28000 32000 33000 5000 15000 modulus Specific kg/m 3700 3650 3600 3500 2900 2400 2000 weight Ultimate MPa 30 40 50 60 55 5 45 compression strength Ultimate MPa 3 4 5 6 5.5 0.3 4 tensile strength Poison's ratio – 0.30 0.28 0.26 0.25 0.24 0.25 0.15 To obtain a reasonable picture of the stress-strain state of the massif, the stress and strain of the in-situ rock massif and the artificial massif are calculated. The simulation model is given as an epure with isolines of main stresses and strains and their numerical values. To visually determine stresses, all isolines have a certain value of stresses in Pa, and correspond to a certain color scale. Table 2 presents the value of the pressure of caved rocks on the massif P , P P , P from different depths 1 2, 3 4 of stopping operations, 1450, 1750, 2000 and 2250 m respectively. Table 2. Pressure of caved rocks on the massif Unit of Parameter Р Р Р Р 1 2 3 4 measurement Pressure of caved rocks on massif MPa 8.5/3.0 10.0/3.5 11.7/4.1 13.2/4.7 vertical/lateral To build stress-strain epures by the method of finite elements, the model is divided into quadrangular finite elements with the dimensions of the initial simulation model adequate to the size of the area of the rock massif under study, Fig. 4. 45 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 Figure 4. Quadrangular grid of finite elements for the initial simulation model of the massif under study 4. Research results In our opinion, enhancement of underground mining technologies that prevent formation of sinkholes on the earth's surface, especially in areas adjacent to industrial and civil areas, is possible due to transition to underground mining technologies with the subsequent backfilling of mined-out areas. Fig. 5 presents a variant of calculating the fields of stresses in complex structured rocks with mined-out stopes of the lower level. According to the technology proposed by the authors that implies transition to mining systems with backfilling the mined-out area, the upper level is mined and backfilled with an artificial hardening mixture. Over the artificial hardening mixture, there are caved waste rocks resulted from mining the upper levels applying classical technologies with overlying rock caving. Figure 5. Isolines of maximum stresses σ in the form of a gradient color diagram in a complex structured massif with mined-out stopes of the lower level, MPa, (ore 1P, pressure P ) Fig. 5 demonstrates the classical overall picture of stress field distribution: the greatest absolute stress value is reached near the corners of the formed stope in the country rocks of the rock massif. Concentration of maximum stresses in the corners of the upper stope backfilled with an artificial hardening material is much lower. This is due to much lower elastic characteristics of the artificial hardening backfill as compared to the monolithic massif of country rocks. Emergence of significant maximum stresses σ in the corners of the stope is explained by the effect of compressive stresses. With deepening into the massif, the stresses σ decrease, and their distribution becomes more uniform. 46 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 It is determined that concentration of maximum stresses σ is observed in the upper and lower corners of stopes that are not backfilled in the artificial backfilled massif and that of the stope hanging wall rocks respectively. In some cases, the side exposures of the stope are characterized by tensile stresses σ occurring in the central part of the side generatrix. In this case, the stresses σ are reduced from the boundary of the stope deep down into the ore massif. It is proved that depending on the calculated stability of stopes, effective maximum stresses σ influence differently the geodynamic state of a complex structured massif. If values of maximum stresses σ1 are far from critical ones, they cannot cause massif failure. It is determined that under the influence of strains, the side surfaces and the crown of the stope can transform and acquire a convex shape. In this case, there appear tensile stresses σ , which can weaken both the crown and the side surfaces of the stope. This applies to both natural rock massif and the artificial hardening massif. In the modern theory of geodynamic stabilization of the rock massif and strains of the daylight surface, it is assumed that when calculating the stress-strain state of the massif as a criterion for assessing stability of exposures, the condition is accepted that main tensile stresses should not exceed the permissible ones. If this condition is not fulfilled, then there will occur complete or partial caving of exposures of workings, since most rocks undergo brittle fracturing when bending. Thus, finding stable sizes of exposures is reduced to determining the stresses acting in them and comparing them with the permissible ones. O. Mohr’s envelope can be considered the most common and complete characteristic of exposure stability. When determining exposure stability, the Mohr criterion [14] can be represented as follows: 𝜎 = 𝜎 +𝑘 𝜎 ≤ [𝜎 ], (1) м 1 3 𝑝 𝑘 = , 𝑝𝑟𝑐𝑜𝑚 where σ , σ are the main minimum and maximum stresses, MPa; σ , σ are ultimate tensile and compression 1 3 р compr strength respectively, MPa. During underground mining operations with formation of stopes, there are created fields of stresses and strains around the stopes, which can be conceived of as the sum of the basic and additionally formed fields of stresses and shears. Considering the effective direct relation between stresses and strains, in this case, solving a three-dimensional problem is reduced to the need for their joint integration [14]: 𝑑 𝜎 𝑑 𝜏 𝑑 𝜏 𝑥 𝑥 𝑧 + + = 0, 𝑑 𝜏 𝑑 𝜎 𝑑 𝜏 + + = 0, (2) 𝑑𝑥 𝑑𝑦 𝑑𝑧 𝑑 𝜏 𝑑 𝜏 𝑑 𝜎 + + = 0. The performed studies enable establishing that with the values of main stresses close to critical ones, effective stresses can cause failure of crowns or intervening pillars followed by failure of the adjacent massif. For instance, maximum compressive stresses in the lower corner in the hanging wall rocks of stopes that are not backfilled are over 26 MPa with the ultimate compression strength of 50 MPa. Thus, their value makes over 50% of the critical values of stability of the hanging wall rocks. At the same time, the maximum compressive stresses in the upper corner of the stope in the hardening backfilled massif are over 20 MPa with the ultimate compression strength of 45 MPa. Thus, their value makes about 45% of the critical values of stability of the hanging wall rocks and the backfill respectively. It is determined that for short-term stability of exposures of stopes before backfilling, such maximum stresses are permissible. But for long-term maintenance of open stoping, such exposures are problematic. Fig. 6 presents maximum strain values of the complex structured rocks and the artificial massif for conditions similar to those presented above. The results of modeling the strain epure can be visualized as a gradient color diagram. The pattern of strains (subsidence) of the massif enables asserting the following. Hardening backfill for the overlying mined-out stope almost stabilizes subsidence of rocks in the hanging wall of the deposit (60.512 mm vs. 60,359 mm). At the same time, subsidence of overlying caved waste rocks above the mined-out stope is characterized by a much larger degree (74.523 mm vs. 60.512 mm) than above the mined-out backfilled one. 𝑑𝑧 𝑑𝑦 𝑑𝑥 𝑧𝑦 𝑧𝑥 𝑦𝑧 𝑥𝑦 𝑑𝑧 𝑑𝑦 𝑑𝑥 𝑦𝑥 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 Figure 6. Strain epures in the form of a gradient color diagram of a complex structured massif with mined-out stopes of the lower level, mm, (ore 1P, pressure P1) 5. Conclusions The obtained results enable asserting that the analytical method of modeling used in the presented work corresponds to the general picture of stress distribution in a complex structured massif and can be used for further research into the geodynamic state of the rock massif by analytical methods. Further application of technologies of mining ore deposits with country rock caving will lead to further subsidence of the rock massif above the mined-out area. Over time, such strains of the rock massif will result in subsidence of the daylight surface in the fields of operating underground mines. This scenario is now observed in the mine fields of operating underground mines throughout Kryvyi Rih iron ore basin. However, as the results of the research demonstrate, application of stoping followed by backfilling the mined-out stopes with the artificial massif of hardening backfill prevents strains of the natural rock massif. Accordingly, application of the technologies proposed by the authors that imply backfilling the mined- out area averts subsidence of the daylight surface in the fields of operating underground mines, and prevents occurrence of dangerous situations within areas of industrial and civil activities. References [1] Stupnik M., Kalinichenko V., Kalinichenko O., Muzyka I., Fedko M., Pysmennyi S. 2015 Information Technologies as a Component of Monitoring and Control of Stress-Deformed State of Rock Mass / Mining of Mineral Deposits, 2015. 9(2). Р.175-181. https://doi.org/10.15407/mining09.02.175 [2] Stupnik M., Kalinichenko V., Kalinichenko E., Muzika І., Fed'ko М., Pis'menniy S. 2015 The Research of Strain-Stress State of Magnetite Quartzite Deposit Massif in the Condition of Mine “Gigant-Gliboka” of Central Iron Ore Enrichment Works (CGOK) / Metallurgical and Mining Industry, 2015. No.7. Р.377-383 [3] Kalinichenko O.V. 2020 Rozvytok naukovykh osnov upravlinnia napruzheno-deformovanym stanom masyvu pry formuvanni pidzemnykh vyrobok: dys...doktora tekhn. nauk: 05.15.02 / O.V. Kalinichenko. Kryvyi Rih, 2020. 405 s [4] Kalinichenko O.V. 2018 Doslidzhennia napruzheno-deformovanoho stanu masyvu matematychnymy metodamy / Vcheni zapysky Tavriiskoho natsionalnoho universytetu im. V.I. Vernadskoho. Seriia “tekhnichni nauky”, 2018. Tom 29 (68). №5. S.133 –137 48 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 [5] Stupnik M., Kalinichenko V., Pysmennyi S., Kalinichenko O. 2019 The Resource-Saving Technology of Mining Complex Structured Iron Ore Deposits / Traditions and Innovations of Resource-Saving Technologies in Mineral Mining and Processing: Multi-Authored Monograph. Petroșani, Romania: Universitas Publishing, 2019. Р. 4 – 21 [6] Stupnik M.I., Kalinichenko V.O., Pysmennyi S.V., Kalinichenko O.V., Pysmenna T.H. 2017 Doslidzhennia vplyvu pidzemnykh hirnychykh robit na vidchuzhennia zemelnykh dilianok v umovakh shakhty “Ternivska” PAT “Kryvbaszalizrudkom” / International Conference “Innovative Technologies in Science and Education. European Experience”. Vienna, Austria, 2017. Р.327-335 [7] Streng G. 1977 Fiks Dzh. Teoriya metoda konechnyih elementov. Mir, 1977. 349 s [8] Parisean W.G. 1987 Estimation of Support Load Requirements of Underground Mine Openings by Computer Simulation of Mining Sequence / Truns. foc. MiningEng. AJME, 1987. Vol. 262. №2 (june). P. 100–109 [9] Amusin B.Z., Fadeev A.B. 1975 Metod konechnyih elementov pri reshenii zadach gornoy geomehaniki. M.: Nedra, 1975. 144 s. [10] Hiks Ch. 1967 Osnovnyie printsipyi planirovaniya eksperimenta: Per. s angl. M.: Mir, 1967. 406 s. [11] Nalimov V.V., Chernova I.L. 1965 Statisticheskie metodyi planirovaniya eksperimentalnyih issledovaniy. M.: Nauka, 1965. 360 s. [12] Barulev A.D. 1994 O vozmozhnosti primeneniya metoda konechnyih elementov dlya rascheta napryazhenno-deformirovannogo sostoyaniya razuplotnyayuschihsya sred / FTRPI, 1994. #1. S. 48–53 [13] Fadeev A.B. 1987 Metod konechnyih elementov v geomehanike. M.: Nedra, 1987. 221 s [14] Grebenyuka V.A., Pyizhyanova Ya.S., Erofeeva I.E. 1983 Spravochnik po gornorudnomu delu / Pod redaktsiey M., Nedra, 1983. 816 s. 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Study and Enhancement of Underground Mining Technologies to Prevent Earth’s Surface Failures

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Abstract

Revista Minelor – Mining Revue ISSN-L 1220-2053 / ISSN 2247-8590 vol. 28, issue 1 / 2022, pp. 42-49 STUDY AND ENHANCEMENT OF UNDERGROUND MINING TECHNOLOGIES TO PREVENT EARTH'S SURFACE FAILURES 1 2 3 4 Mykola STUPNIK , Olena KALINICHENKO , Mykhailo FEDKO , Mykhailo HRYSHCENKO , 5 6* 7 Vsevolod KALINICHENKO , Serhii CHUKHAREV , Sofiia YAKOVLEVA , Alexey POCHTAREV Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine Kryvyi Rih National University, Dept. of Underground Mining of Useful Mineral Deposits, Kryvyi Rih, Ukraine LAMET s.r.o., Bellova 3, 04001 Košice office: Rozvojovά 2 A, Slovakia DOI: 10.2478/minrv-2022-0004 Abstract: The work contains studies of the problem of stabilizing geodynamic processes in the rock massif, preservation of the daylight surface and ecological balance in the mined-out and operating mine fields of Ukraine. The main regularities of influence of sublevel-room mining systems with backfilling on changes of the stress-strain state of the rock massif and the main structural elements of the block are determined. Rich iron ore mining by underground methods and subsequent transition to the sublevel-room mining system with backfilling is modeled. New technologies for mining ore deposits are developed and current ones are enhanced to prevent the earth’s surface failures, stabilize landslide and displacement zones within the boundaries existing at the time of transition to systems with backfilling. The developed resource-saving technologies of mining can significantly enhance ore extraction indicators and the environmental condition of the basin by locating waste dumps and disposing wastes of mining enterprises in the mined-out area of underground mines. Keywords: underground mining, stress-strain state, rich iron ores, magnetite quartzite, ore drawing, flowsheet 1. Introduction Mining deposits by underground methods results in formation of significant undermined areas. As a rule, the main characteristic of these areas is the disturbed daylight surface with terraced zones and sometimes subsidence that endanger human production and civil activities. Currently, in Ukraine and worldwide, influence of underground mining on the daylight surface stability is insufficiently studied. Existing studies are usually region-related. In our opinion, it is necessary to develop new integrated technologies that allow conducting high-efficiency underground mining with simultaneous disposal of mining wastes in mined-out areas of underground mines and preservation of the daylight surface and existing urban structures. Therefore, the study of regularities of stabilization of geodynamic processes in the rock massif and development of resource-saving technologies for mining various grade iron ores and development of technological solutions to prevent subsidence of the earth’s surface in iron ore underground mining is an urgent scientific and technical problem of significant scientific, environmental and practical and technological importance. Corresponding author: Serhii Chukharev, Kryvyi Rih National University, Kryvyi Rih, Ukraine, contact details (e-mail:konf.knu@gmail.com) 42 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 2. Analysis of the problem of preserving the daylight surface in mined-out and operating mine fields of Ukraine Extraction of significant volumes of minerals changes the stress-strain state of rocks, which in turn affects the processes of rock massif displacement when it can reach the earth’s surface and destruct industrial and civil objects located in this area. Extraction of salt in Kalush mining district (1867 - 2007) by underground mines Kalush and Novo-Holyn is an example of the situation of this kind. Technogenic activities caused a threat of a trans-boundary water- environmental emergency (WES) in Dniester river basin and were hazardous to human health and safety. The resulted strain of the earth’s surface over underground mining stopes of about 17 M m causes significant subsidence of the earth’s surface with brine displacement, formation of salt lakes and sudden sinkholes, with damage to and destruction of buildings and structures in Kalush and nearby villages. The first subsidence on the earth’s surface in Kalush occurred in the summer of 1987 on Parkhomenko (now Vitovskyi) Street (Fig. 1). The depth of the sinkhole was up to 8.5 meters. Nearly two dozen homes were under threat. In 2008, another sinkhole occurred in the same neighborhood and in the autumn of 2015 – another one only a few meters away from the old one. Subsequently, these sinkholes combined. Figure 1. The first subsidence in Kalush At present, the daylight surface subsidence within the mine area varies from 0.5 m to 5.1 m, the forecast values reach up to 7.1-9.1 m, which under activated karstification significantly aggravates the engineering and geological conditions of Kalush basin. Kryvyi Rih iron ore basin faces similar problems. Relevance of geo-mechanical researches is so significant that they are conducted at almost all large mining enterprises. Moreover, there have been made numerous attempts to summarize the results of the researches and present them in the form of separate general regularities. However, in general, these studies are, as a rule, region-related. Thus, on 13 June, 2010, at Ordzhonikidze underground mine, immediately after the planned blasting operations, there occurred intensive daylight surface failure in the mine allotment zone within survey axes (- 37)–(45). The total area of the failure made 16.5 ha (Fig. 2). 43 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 Figure 2. Daylight surface failure in the Ordzhonikidze mine allotment zone On 17 August, 2010, in the Tsentralno-Miskyi district of Kryvyi Rih (5, Urytskyi Street) a partial failure of the earth’s surface between 3 am – 6 am resulted in a crater within survey axes 57–58 and the average strike line (ASL) from +30 to +50 (Fig. 3). The failure is located in the mine field of the HPU mine (closed down in 1972) and above the mine workings resulted from iron ore mining. The topographic survey performed by the specialists of the State Enterprise “DPI “Kryvbasproekt” showed that the diameter of the crater reached 18 m, and its volume made 1500-1600 m , i.e. nearly 1700- 1800 m of underground voids was filled due to failure. Fig. 3 presents the failed area of the daylight surface in the mining allotment zone of the HPU mine that was closed in 1972. Figure 3. The failed area of the daylight surface in the mining allotment zone of the HPU mine Unfortunately, such phenomena are not sporadic for Kryvyi Rih iron ore basin. One of the main conclusions drawn from the given data can be expressed as follows: today's expenditures for implementing measures to prevent possible emergencies are much lower than the future costs of eliminating consequences of such definitely possible situations. One of the ways to prevent emergencies on the daylight surface within mining allotments of Kryvyi Rih basin underground mines consists in applying technologies of underground mining with the subsequent backfilling of the mined-out areas. 44 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 3. Research methods The criterion for the study and enhancement of underground mining technologies that prevent formation of sinkholes is selection of the optimal concept of research of the stress-strain state of the rock massif and daylight surface failures during ore mining operations that cause significant mined-out areas. Currently, a significant number of analytical methods and computer programs are used to calculate and model distribution of stresses in the rock massif around the mined-out area. Classical modeling by the finite elements method is the most common [4, 7, 9, 12, and 13]. In general, based on results of modeling by the method of finite elements, it is affirmed that when stresses in certain areas of the massif exceed permissible ones, the rock massif begins failing. To study and enhance the underground mining technologies that prevent failures of the earth’s surface, the following application programs enabling determination of the stress-strain state of the rock massif are used: “SolidWorks”, “Lira”, “Ansys”, “GTSNX”, “SCAD”, etc. Such programs help study strains of the rock massif both on mined-out ore deposit levels and the daylight surface. In the course of the research, the finite elements method and the ANSYS 2021 software complex are used to solve the problems related to determining the geodynamic state of the rock massif, fields of stresses and calculating strains of the rock massif around the mined-out area and on the daylight surface [1–3, 5, 6, 8, 10, and 11]. Table 1 presents the initial physical and mechanical properties of the rock and the backfilling material used when calculating stresses and strains. Table 1. Physical and mechanical properties of the rock and the backfilling material Ore Rock Backfill Unit of Caved Parameter 1Р 2Р 3Р 4Р П measurement rocks f=3-5 f=4-6 f=5-7 f=6-8 f=5-7 Young's MPa 22000 25000 28000 32000 33000 5000 15000 modulus Specific kg/m 3700 3650 3600 3500 2900 2400 2000 weight Ultimate MPa 30 40 50 60 55 5 45 compression strength Ultimate MPa 3 4 5 6 5.5 0.3 4 tensile strength Poison's ratio – 0.30 0.28 0.26 0.25 0.24 0.25 0.15 To obtain a reasonable picture of the stress-strain state of the massif, the stress and strain of the in-situ rock massif and the artificial massif are calculated. The simulation model is given as an epure with isolines of main stresses and strains and their numerical values. To visually determine stresses, all isolines have a certain value of stresses in Pa, and correspond to a certain color scale. Table 2 presents the value of the pressure of caved rocks on the massif P , P P , P from different depths 1 2, 3 4 of stopping operations, 1450, 1750, 2000 and 2250 m respectively. Table 2. Pressure of caved rocks on the massif Unit of Parameter Р Р Р Р 1 2 3 4 measurement Pressure of caved rocks on massif MPa 8.5/3.0 10.0/3.5 11.7/4.1 13.2/4.7 vertical/lateral To build stress-strain epures by the method of finite elements, the model is divided into quadrangular finite elements with the dimensions of the initial simulation model adequate to the size of the area of the rock massif under study, Fig. 4. 45 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 Figure 4. Quadrangular grid of finite elements for the initial simulation model of the massif under study 4. Research results In our opinion, enhancement of underground mining technologies that prevent formation of sinkholes on the earth's surface, especially in areas adjacent to industrial and civil areas, is possible due to transition to underground mining technologies with the subsequent backfilling of mined-out areas. Fig. 5 presents a variant of calculating the fields of stresses in complex structured rocks with mined-out stopes of the lower level. According to the technology proposed by the authors that implies transition to mining systems with backfilling the mined-out area, the upper level is mined and backfilled with an artificial hardening mixture. Over the artificial hardening mixture, there are caved waste rocks resulted from mining the upper levels applying classical technologies with overlying rock caving. Figure 5. Isolines of maximum stresses σ in the form of a gradient color diagram in a complex structured massif with mined-out stopes of the lower level, MPa, (ore 1P, pressure P ) Fig. 5 demonstrates the classical overall picture of stress field distribution: the greatest absolute stress value is reached near the corners of the formed stope in the country rocks of the rock massif. Concentration of maximum stresses in the corners of the upper stope backfilled with an artificial hardening material is much lower. This is due to much lower elastic characteristics of the artificial hardening backfill as compared to the monolithic massif of country rocks. Emergence of significant maximum stresses σ in the corners of the stope is explained by the effect of compressive stresses. With deepening into the massif, the stresses σ decrease, and their distribution becomes more uniform. 46 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 It is determined that concentration of maximum stresses σ is observed in the upper and lower corners of stopes that are not backfilled in the artificial backfilled massif and that of the stope hanging wall rocks respectively. In some cases, the side exposures of the stope are characterized by tensile stresses σ occurring in the central part of the side generatrix. In this case, the stresses σ are reduced from the boundary of the stope deep down into the ore massif. It is proved that depending on the calculated stability of stopes, effective maximum stresses σ influence differently the geodynamic state of a complex structured massif. If values of maximum stresses σ1 are far from critical ones, they cannot cause massif failure. It is determined that under the influence of strains, the side surfaces and the crown of the stope can transform and acquire a convex shape. In this case, there appear tensile stresses σ , which can weaken both the crown and the side surfaces of the stope. This applies to both natural rock massif and the artificial hardening massif. In the modern theory of geodynamic stabilization of the rock massif and strains of the daylight surface, it is assumed that when calculating the stress-strain state of the massif as a criterion for assessing stability of exposures, the condition is accepted that main tensile stresses should not exceed the permissible ones. If this condition is not fulfilled, then there will occur complete or partial caving of exposures of workings, since most rocks undergo brittle fracturing when bending. Thus, finding stable sizes of exposures is reduced to determining the stresses acting in them and comparing them with the permissible ones. O. Mohr’s envelope can be considered the most common and complete characteristic of exposure stability. When determining exposure stability, the Mohr criterion [14] can be represented as follows: 𝜎 = 𝜎 +𝑘 𝜎 ≤ [𝜎 ], (1) м 1 3 𝑝 𝑘 = , 𝑝𝑟𝑐𝑜𝑚 where σ , σ are the main minimum and maximum stresses, MPa; σ , σ are ultimate tensile and compression 1 3 р compr strength respectively, MPa. During underground mining operations with formation of stopes, there are created fields of stresses and strains around the stopes, which can be conceived of as the sum of the basic and additionally formed fields of stresses and shears. Considering the effective direct relation between stresses and strains, in this case, solving a three-dimensional problem is reduced to the need for their joint integration [14]: 𝑑 𝜎 𝑑 𝜏 𝑑 𝜏 𝑥 𝑥 𝑧 + + = 0, 𝑑 𝜏 𝑑 𝜎 𝑑 𝜏 + + = 0, (2) 𝑑𝑥 𝑑𝑦 𝑑𝑧 𝑑 𝜏 𝑑 𝜏 𝑑 𝜎 + + = 0. The performed studies enable establishing that with the values of main stresses close to critical ones, effective stresses can cause failure of crowns or intervening pillars followed by failure of the adjacent massif. For instance, maximum compressive stresses in the lower corner in the hanging wall rocks of stopes that are not backfilled are over 26 MPa with the ultimate compression strength of 50 MPa. Thus, their value makes over 50% of the critical values of stability of the hanging wall rocks. At the same time, the maximum compressive stresses in the upper corner of the stope in the hardening backfilled massif are over 20 MPa with the ultimate compression strength of 45 MPa. Thus, their value makes about 45% of the critical values of stability of the hanging wall rocks and the backfill respectively. It is determined that for short-term stability of exposures of stopes before backfilling, such maximum stresses are permissible. But for long-term maintenance of open stoping, such exposures are problematic. Fig. 6 presents maximum strain values of the complex structured rocks and the artificial massif for conditions similar to those presented above. The results of modeling the strain epure can be visualized as a gradient color diagram. The pattern of strains (subsidence) of the massif enables asserting the following. Hardening backfill for the overlying mined-out stope almost stabilizes subsidence of rocks in the hanging wall of the deposit (60.512 mm vs. 60,359 mm). At the same time, subsidence of overlying caved waste rocks above the mined-out stope is characterized by a much larger degree (74.523 mm vs. 60.512 mm) than above the mined-out backfilled one. 𝑑𝑧 𝑑𝑦 𝑑𝑥 𝑧𝑦 𝑧𝑥 𝑦𝑧 𝑥𝑦 𝑑𝑧 𝑑𝑦 𝑑𝑥 𝑦𝑥 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 Figure 6. Strain epures in the form of a gradient color diagram of a complex structured massif with mined-out stopes of the lower level, mm, (ore 1P, pressure P1) 5. Conclusions The obtained results enable asserting that the analytical method of modeling used in the presented work corresponds to the general picture of stress distribution in a complex structured massif and can be used for further research into the geodynamic state of the rock massif by analytical methods. Further application of technologies of mining ore deposits with country rock caving will lead to further subsidence of the rock massif above the mined-out area. Over time, such strains of the rock massif will result in subsidence of the daylight surface in the fields of operating underground mines. This scenario is now observed in the mine fields of operating underground mines throughout Kryvyi Rih iron ore basin. However, as the results of the research demonstrate, application of stoping followed by backfilling the mined-out stopes with the artificial massif of hardening backfill prevents strains of the natural rock massif. Accordingly, application of the technologies proposed by the authors that imply backfilling the mined- out area averts subsidence of the daylight surface in the fields of operating underground mines, and prevents occurrence of dangerous situations within areas of industrial and civil activities. References [1] Stupnik M., Kalinichenko V., Kalinichenko O., Muzyka I., Fedko M., Pysmennyi S. 2015 Information Technologies as a Component of Monitoring and Control of Stress-Deformed State of Rock Mass / Mining of Mineral Deposits, 2015. 9(2). Р.175-181. https://doi.org/10.15407/mining09.02.175 [2] Stupnik M., Kalinichenko V., Kalinichenko E., Muzika І., Fed'ko М., Pis'menniy S. 2015 The Research of Strain-Stress State of Magnetite Quartzite Deposit Massif in the Condition of Mine “Gigant-Gliboka” of Central Iron Ore Enrichment Works (CGOK) / Metallurgical and Mining Industry, 2015. No.7. Р.377-383 [3] Kalinichenko O.V. 2020 Rozvytok naukovykh osnov upravlinnia napruzheno-deformovanym stanom masyvu pry formuvanni pidzemnykh vyrobok: dys...doktora tekhn. nauk: 05.15.02 / O.V. Kalinichenko. Kryvyi Rih, 2020. 405 s [4] Kalinichenko O.V. 2018 Doslidzhennia napruzheno-deformovanoho stanu masyvu matematychnymy metodamy / Vcheni zapysky Tavriiskoho natsionalnoho universytetu im. V.I. Vernadskoho. Seriia “tekhnichni nauky”, 2018. Tom 29 (68). №5. S.133 –137 48 Revista Minelor – Mining Revue vol. 28, issue 1 / 2022 ISSN-L 1220-2053 / ISSN 2247-8590 pp. 42-49 [5] Stupnik M., Kalinichenko V., Pysmennyi S., Kalinichenko O. 2019 The Resource-Saving Technology of Mining Complex Structured Iron Ore Deposits / Traditions and Innovations of Resource-Saving Technologies in Mineral Mining and Processing: Multi-Authored Monograph. Petroșani, Romania: Universitas Publishing, 2019. Р. 4 – 21 [6] Stupnik M.I., Kalinichenko V.O., Pysmennyi S.V., Kalinichenko O.V., Pysmenna T.H. 2017 Doslidzhennia vplyvu pidzemnykh hirnychykh robit na vidchuzhennia zemelnykh dilianok v umovakh shakhty “Ternivska” PAT “Kryvbaszalizrudkom” / International Conference “Innovative Technologies in Science and Education. European Experience”. Vienna, Austria, 2017. Р.327-335 [7] Streng G. 1977 Fiks Dzh. Teoriya metoda konechnyih elementov. Mir, 1977. 349 s [8] Parisean W.G. 1987 Estimation of Support Load Requirements of Underground Mine Openings by Computer Simulation of Mining Sequence / Truns. foc. MiningEng. AJME, 1987. Vol. 262. №2 (june). P. 100–109 [9] Amusin B.Z., Fadeev A.B. 1975 Metod konechnyih elementov pri reshenii zadach gornoy geomehaniki. M.: Nedra, 1975. 144 s. [10] Hiks Ch. 1967 Osnovnyie printsipyi planirovaniya eksperimenta: Per. s angl. M.: Mir, 1967. 406 s. [11] Nalimov V.V., Chernova I.L. 1965 Statisticheskie metodyi planirovaniya eksperimentalnyih issledovaniy. M.: Nauka, 1965. 360 s. [12] Barulev A.D. 1994 O vozmozhnosti primeneniya metoda konechnyih elementov dlya rascheta napryazhenno-deformirovannogo sostoyaniya razuplotnyayuschihsya sred / FTRPI, 1994. #1. S. 48–53 [13] Fadeev A.B. 1987 Metod konechnyih elementov v geomehanike. M.: Nedra, 1987. 221 s [14] Grebenyuka V.A., Pyizhyanova Ya.S., Erofeeva I.E. 1983 Spravochnik po gornorudnomu delu / Pod redaktsiey M., Nedra, 1983. 816 s. 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Journal

Mining Revuede Gruyter

Published: Mar 1, 2022

Keywords: underground mining; stress-strain state; rich iron ores; magnetite quartzite; ore drawing; flowsheet

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