Taking a large scale ferrous metallurgical underground mine in Hubei Province, China as an example, the regional multi-hazard risk assessment is carried out for the risk points of cage falling accident, fire accident, water inrush accident and roof fall and rib spalling accident involved in this underground mine, and corresponding risk control strategies are proposed to verify the feasibility and reliability of the model.
Mine overview
The main product of this iron ore is magnetite, with an annual capacity of 1.3 million tons. The surrounding rocks of the ore body roof mainly include skarn, marble, dolomitic marble and skarn diorite, while the surrounding rocks of the ore body floor mainly include skarn, skarn diorite and biotite pyroxene diorite. The orebody belongs to inclined ~ steeply inclined and medium thick ~ thick ore body. The stability of the ore is moderately stable ~ stable, and the surrounding rock of the roof and floor is moderately stable ~ stable. The ore is dominated by massive magnetite-rich and mixed-rich.
The mine adopts shaft development, and the main mining sections are − 50 m, − 110 m and − 170 m. The ore is mainly lifted from phase I main shaft, phase II main shaft and phase III main shaft. The design lifting capacity of phase I main shaft is 700,000 tons, phase II main shaft is 300,000 tons, and phase III main shaft is 450,000 tons. Underground transportation adopts electric locomotive to transport ore.
The mining method is sublevel open stope and subsequent filling method, Simba 1252 medium and deep hole rock drilling jumbo drilling, granular ANFO explosive and non-electric blasting system blasting, 3m3 electric or diesel scraper concentrated at the bottom of the stope for ore extraction, and after the stope stoping is completed, full tailings filling is used for cemented filling of the goaf.
Diagonal mechanical forced ventilation is adopted, the return air shaft is equipped with exhaust equipment, and local fans are used for auxiliary ventilation in local areas with poor ventilation. There is a ventilation monitoring system to monitor the air volume, wind speed and wind quality of each mining area. In addition, the mine implements wet rock drilling, and the crushing base station is equipped with a closed dust hood for dust removal.
Multi-hazard risk measurement
(1) Risk assessment of cage falling accident risk point.
The safety protection device of the auxiliary shaft cage of the mine is normal, the steel wire rope braking system and the hoist system are normal, and reliable overwinding protection devices and fall arresters are set. Hazard index of hazardous equipment and facilities is hs = 1.2.
The depth of the auxiliary shaft in the mining is 190 m, and the hazard index of hazardous substances M = 1 is determined by the depth of the auxiliary shaft.
The working system of the mine is 3 shifts/day, 8 h per shift, 150 people in the morning shift, 60 people in the middle shift and 60 people in the evening shift in the mine. According to the maximum number of people in the cage is 48, the hazard index of hazardous places is determined to be E1 = 7.
The steel wire rope of the hoisting system has complete inspection records, but the steel wire rope online monitoring system has not been built. In addition, video monitoring facilities and other monitoring facilities are normal. Hazard index of hazardous processes K1 = 1.5.
The hazardous operations involved in the risk points of cage falling accidents include equipment maintenance operations, elevator operations, non-coal mine safety inspection operations, and non-coal mine hoist operations. The risk correction coefficient of hazardous operations K2 = 1.2.
Therefore, the inherent risk index H1 = 1.2 × 1 × 7 × 1.5 × 1.2 = 15.12 for the risk point of cage falling in the mine.
The system vulnerability of the cage falling accident of the mine V = 1–0.07–0.01–0.15–0.18–0.225 = 0.365.
The safety production standardization level of the underground mine is level I, taking v = 90, that is, the risk control index G = 1.11.
The risk of the risk point of the tank falling accident of the mine R1 = GHV = 6.13.
(2) Risk assessment of fire accident risk point.
The mine has obvious fire prevention signs and precautions. The duty room at the entrance of the auxiliary ramp is equipped with fire-fighting equipment, mainly including dry powder fire extinguishers, gas masks, etc. A certain amount of sand is stacked on the surface for fire extinguishing. Each trackless self-propelled equipment (including underground LHD, rock drilling jumbo, material truck, etc.) is equipped with fire extinguishing devices. Operators and temporary personnel must wear a self-rescuer when going down the shaft. However, the mine is not equipped with automatic fire extinguishing facilities. Therefore, the hazard index of hazardous equipment and facilities is hs = 1.175.
There is diesel fuel stored in the well, a 3 m3 tank in the bottom of the well yard and a 180L drum at the working face, with an oil hazard index of M1 = 1. Ore product is mainly magnetite, no spontaneous combustion tendency, ore hazard index M2 = 1. The cables and supports under the mine are non-flame-retardant materials, and the hazard index of non-flame-retardant materials M3 = 1. M = max(M1,M2,M3) = 1.
The maximum number of people working in a single shift under the mine is 150. Considering the anti-wind system and the number of people affected by a fire in the underground yard is calculated as 100, the hazard index of the hazardous places is determined as E2 = 9.
There are monitoring facilities such as toxic and hazardous gas detection devices and temperature alarms built under the mine, which are all operating normally and have good air quality. Hazard index of hazardous processes K1 = 1.
The hazardous operations involved in fire accident risk points include temporary power operation, fire work, pressure vessel operation, welding and thermal cutting operation, non-coal mine safety inspection operation, non-coal mine underground electrical operation, and mine ventilation operation. The risk correction coefficient of hazardous operations K2 = 1.35.
Therefore, the inherent risk index H2 = 1.175 × 1 × 9 × 1 × 1.35 = 14.28 for the risk point of cage falling in the mine.
The system vulnerability of the fire accident of the mine V = 1–0.069–0.011–0.2–0.15–0.203 = 0.567.
The risk control index G = 1.11.
The risk of the risk point of the fire accident of the mine R2 = GHV = 8.99.
(3) Risk assessment of mine water inrush accident risk point.
Surface waterproofing measures and facilities in the mine area include: interception and drainage ditches have been excavated around the mine area to effectively intercept the convergence of surface water from the surrounding areas to the collapse area; waterproofing inspections are organized and manned during the rainy season every year. The main waterproofing measures in the underground mine: water exploration work was carried out in the newly mined area, and waterproof doors were installed in each of the main production sections − 50 m, − 110 m and − 170 m at the bottom of the shaft yard; the water outlet points with a large amount of water gushing from the shaft were sealed; the main drainage equipment and facilities are nine 200D43 × 8 pumps with a head of 344 m and a flow rate of 280m3/h. Therefore, the hazard index of hazardous equipment and facilities is hs = 1.14.
The hydrogeological conditions of the mine area belong to simple to moderately complex type; the maximum water inflow is 24430 m3/day, the normal water inflow is 3432 m3/day. The hazard index of hazardous materials M = 4.
The lowest middle section of the mine is − 170 m, the maximum number of workers in a single shift is about 30, and the hazard index of hazardous places is determined to be E3 = 9.
The surface of the mining area is equipped with precipitation monitoring, and the underground is equipped with monitoring facilities such as pit water inflow monitoring, which are operating normally. The mining area has completed the water exploration work in the newly opened area, and currently there is no water exploration work surface, and the water exploration work surface is monitored by video. Hazard index of hazardous processes K1 = 1.
The hazardous operations involved in the risk points of water inrush accidents are water exploration and drainage operations, mine safety inspection operations, and mine drainage operations in three categories, with the high-risk operation hazard correction factor K2 = 1.15.
Therefore, the inherent risk index H3 = 1.175 × 1 × 9 × 1 × 1.35 = 47.20 for the risk point of water inrush in the mine.
The system vulnerability of the water inrush accident of the mine V = 1–0.067–0.044–0.2–0.15–0.173 = 0.366.
The risk control index G = 1.11.
The risk of the risk point of the water inrush accident of the mine R3 = GHV = 19.0.
(4) Risk assessment of roof fall and rib spalling inrush accident risk point.
According to the engineering geological characteristics of rock discontinuity structural plane and structural body, the rocks in the mining area are divided into three engineering geological rock groups. Massive rock group: mainly thick to mega-thick layered limestone and granitic diorite porphyry, dominated by massive structure, with RQD value of 50–80%, which is a grade II rock body, and grade IV rock body at broken places. Loose structure rock group: It is mainly the surface quaternary strata and the loose rock formation in the fracture belt, belonging to class V rock mass. Therefore, the hazard index of hazardous equipment and facilities is hs = 1.175.
At present, the mine adopts the filling method for mining, the goaf is treated completely, the roadway is supported by shotcrete-bolt mesh in the whole process, and the local unstable area is supported by I-steel support. The hazard index of hazardous materials M = 1.
The working system of the mine is 3 shifts/day, 8 h per shift, and 5 people per shift for a single stope work surface. High risk site hazard index E4 = 3.
Surface subsidence monitoring facilities have been built on the surface of the mine area, and some ground pressure activity areas have ground pressure monitoring facilities, and the monitoring data can be obtained normally. Hazard index of hazardous processes K1 = 1.25.
The hazardous operations involved in the risk point of roof fall and rib spalling accident are mine safety inspection operation, mine pillar operation, mine blasting operation 3 categories, high-risk operation hazard correction factor K2 = 1.15.
Therefore, the inherent risk index H4 = 1.175 × 1 × 3 × 1.25 × 1.15 = 5.07 for the risk point of roof fall and rib spalling in the mine.
The system vulnerability of the roof fall and rib spalling accident of the mine V = 1–0.069–0.011–0.067–0.188–0.173 = 0.492.
The risk control index G = 1.11.
The risk of the risk point of the roof fall and rib spalling accident of the mine R4 = GHV = 3.11.
The metal underground mine is under the greatest threat of water inrush accident, followed by fire accident, cage falling accident and roof fall and rib spalling accident.
Based on the Nemerow pollution index method for regional risk aggregation, the regional multi-hazard risk index of non-coal underground mine system is obtained, (R_{C} = sqrt {19^{2} + 9.31^{2} /2}) = 21.2. According to the safety risk classification standard of non-coal underground mines in Table 6, the safety risk level of the underground mine is level IV.
Cooperative management and control strategy of multi-hazard risk
Risk control measures for the risk point of the roof fall and rib spalling accident.
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(1)
Reduce the stress concentration zones as far as possible in the mining technical scheme;
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(2)
Strengthen the roadway support work. Graded support should be implemented according to the stability of the rock mass, and the basis of graded support should be reliable, especially the broken section should be designed separately and should be supported in time.
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(3)
Ground pressure monitoring measures are taken in necessary areas. Ground pressure monitoring is recommended in areas where stress is relatively concentrated.
Risk control measures for the risk point of the cage falling accident.
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(1)
Recommends enhanced inspection of well tower structures, anti-over-coil devices, and loading and unloading facilities.
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(2)
It is suggested to improve the inspection items, standards and methods of the daily checklist.
Risk control measures for the risk point of the mine water inrush accident.
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(1)
A comprehensive analysis of mine water flow over the years to identify their patterns.
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(2)
Revise and improve the emergency plan for underground waterproofing, and organize drills.
In addition, the future operation of the mine should continue to implement the safety management system, strengthen the daily inspection of safety facilities such as cages, combustible storage areas, drainage facilities and monitoring facilities, and deal with the problems found in a timely manner, and make the corresponding records and archiving work.
