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Underground mining is a method of extracting ore by entering the interior of the ore body through shaft and tunnel engineering when the ore body is buried deep or open-pit mining is uneconomical. This article mainly introduces the methods and processes of underground mining.
Different geological conditions, orebody characteristics and mining requirements determine different mining methods. The main underground mining methods include: empty field method, filling method, caving method and long wall method.
During the mining process of the empty field method, the goaf area is not temporarily filled. The stability of the goaf area is mainly maintained by the strength of the pillar and the surrounding rock itself. This method has a large stope space, is convenient for the operation of large-scale equipment, and has high production efficiency. However, it has very high requirements for the stability of the ore body and surrounding rock.
The filling method is a technique that uses waste rock, tailings or cementing materials to fill the goed-out area after mining, which serves to support the surrounding rock, reduce surface subsidence and control ground pressure activities. It is suitable for mining high-value ore bodies, in weak surrounding rock conditions, and for use in areas with high environmental protection requirements.
The caving method involves the planned caving of surrounding rock or ore bodies and the release of ore by means of gravity. It is mostly suitable for the mining of large-scale low-grade ore bodies.
The long-wall method is mainly used in coal mining. It involves continuous coal mining with mechanical equipment. As the working face advances, the roof will collapse along with the mining. This method has high mining efficiency, large output and is easy to achieve automation.
Underground mining is a complex and technology-intensive systematic project, and its process covers five major links: development, mining approval, mining recovery, support and transportation.
Development engineering is the foundation of underground mining. Its main purpose is to establish transportation, ventilation, drainage and power supply systems connecting the surface and the ore body by excavating vertical shafts, inclined shafts or horizontal adits and other channels.
Vertical shaft development: It is suitable for mines where the ore body is buried relatively deep (> 200 meters) and the strike length is short. Shafts usually adopt circular or rectangular cross-sections. Circular shafts have lower support costs and better stability. Their diameters are generally 3 to 6 meters, and the depth can reach over 1,000 meters. During the construction process, special techniques such as freezing method and grouting method are often adopted to cross complex geological layers to ensure the stability and sealing of the wellbore.
Inclined shaft development: It is suitable for ore bodies with a relatively gentle inclination (15°-45°). The slope of the inclined shaft is generally controlled at 15°-30°, which is convenient for the operation of mine cars or belt conveyors. The cross-sectional dimensions of inclined shafts are usually determined by transportation equipment. Compared with vertical shafts, the construction difficulty of inclined shafts is lower, but energy consumption increases when the transportation distance is longer.
Horizontal adit development: Low cost and high safety, it is mostly suitable for areas where the ore body is located on slopes or in areas with significant surface undulations. The cross-sectional shape of horizontal adit is mostly arched. The height and width are designed according to the transportation requirements, usually with a height of ≥2.5 meters and a width of ≥3 meters. Horizontal adits not only undertake the transportation of ores but also serve as ventilation and escape routes.
The mining approval project is carried out on the basis of the development project. It divides the mining area through the excavation of roadways and arranges channels for rock drilling, ore extraction, ventilation, etc., to create conditions for mining operations. The goal is to cut the ore body into several relatively independent units to ensure the efficiency and safety of the mining process.
Mining area division: Based on the thickness, dip Angle and ore properties of the ore body, the ore body is divided into multiple mining areas. The length of each mining area is generally 50 to 150 meters, the width is the thickness of the ore body, and the height is determined according to the mining method. Isolation pillars are set up between mining areas to ensure the stability of adjacent mining areas during the mining process.
Roadway layout: It mainly includes drilling roadways, ore discharge roadways and ventilation roadways. Rock drilling roadways are used to arrange drilling equipment, and the cross-sectional dimensions need to meet the operating space requirements of rock drilling jumbos. The ore discharge roadway is connected to the transportation system. Common ones include chutes and transportation level roadways. The diameter of the chutes is generally 2 to 3 meters and they are used for the gravity transportation of the ore. Ventilation tunnels ensure the circulation of air within the mining area and dilute the concentration of harmful gases.
Mining is the core of underground mining. Through methods such as drilling, blasting or mechanical cutting, ores are separated from the ore body. This stage directly determines the output and quality of the ore. The selection of its process needs to comprehensively consider the conditions of the ore body, equipment capacity and safety requirements.
Drilling and blasting method: First, use down-the-hole drills, rock drilling jumpers and other equipment to drill blast holes in the stope. The diameter of the blast holes is usually 70-100mm, and the depth is determined according to the stope height. Subsequently, explosives were loaded for blasting. Commonly used explosives include emulsion explosives and ammonium oil explosives. After blasting, ventilation, smoke exhaust and turquoise treatment should be carried out to ensure the safety of the workers. It is mostly suitable for ore bodies of various hardness levels.
Mechanized cutting method: It uses equipment such as roadheaders and continuous mining machines to directly cut ores, which is suitable for ore bodies with medium hardness or less. However, such equipment requires a large initial investment and has high requirements for the conditions of the ore body.
Support engineering is a key measure to prevent rock layer collapse and ensure the safety of mining operations. According to the stability of the surrounding rock, anchor bolt support, shotcrete support, steel arch frame support or a combination of multiple support methods can be selected.
Anchor bolt support: By anchoring anchor bolts (1.5-3 meters in length) in stable rock strata to form an integral part with the surrounding rock, the self-bearing capacity of the rock strata is enhanced. Anchor rod materials include metals, resins and cement, etc. For fractured rock strata, prestressed anchor rods are often used to enhance the support effect.
Shotcrete support: By using a shotcrete machine to spray concrete onto the rock surface, a support layer with a thickness of 5 to 15 centimeters is formed, which serves to seal the surrounding rock, prevent weathering and reinforce the rock mass.
Steel arch frame support: In areas with extremely poor surrounding rock stability, steel arch frames made of steel materials such as I-beams and U-shaped steel are used for support. The spacing of steel arch frames is generally 0.5 to 1.5 meters, and they need to be used in combination with anchor rods and shotcrete to form a rigid support structure.
The transportation system is responsible for transporting the mined ore from underground to the surface. Depending on the transportation distance, ore output and roadway conditions, mine car transportation, belt transportation or trackless equipment transportation can be selected.
Mine car transportation: A traditional mode of transportation, suitable for small and medium-sized mines or short-distance transportation. The commonly used types of mine cars include fixed mine cars and flip-type mine cars, with a volume generally ranging from 1 to 5 cubic meters. They are pulled by electric locomotives or winches.
Belt transportation: It can transport continuously, with a transportation capacity of over 1,000 tons per hour, and is suitable for long-distance and high-volume ore transportation. The belt width of the belt conveyor is generally 650-1200 millimeters, with a belt speed of 1-3 meters per second. It can achieve automatic control and unattended operation.
Trackless equipment transportation: The five key processes of underground mining are interlinked. Each link needs to be scientifically designed and precisely managed based on the geological conditions of the ore body, mining technical conditions and economic indicators. With the development of intelligent and automated technologies, underground mining is moving towards high efficiency, safety and greenness, providing technical support for the sustainable development of mineral resources.
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