Miners must consider rock mechanics when designing mines and exploiting resources. Coal remains a vital resource for countries like China, where coal consumption covers 57% of its energy needs. However, deep excavation carries an increased risk of catastrophic failures. Advanced knowledge of rock mechanics will help inform the future of mine planning and resource development. This article will address this topic, exploring current, new and future developments in the field.
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How rock mechanics affect mining
Road and mine site engineering requires an intimate knowledge of rock mechanics to avoid potential disasters. Mines exploit deeper resources due to increasing demand for energy and depletion of shallower reserves.
As mines increase in depth, the rocks encountered can exhibit characteristics such as strong rheology and high degrees of deformation. Deep mining disasters such as collapses, critical deformation of surrounding rocks and gas explosions are on the rise. This presents dangers to life and property as well as increased costs for mining operations. As a result, research on rock mechanics in mining is increasingly concentrated among companies and scientists.
Recent advances in research in the field have provided relevant information on several factors in rock mechanics. This includes the theory of deep high stress induction, the fracture and strength characteristics of rocks found in deep mining, the mechanisms of fracture induction, the theories of multiple infiltration under high disturbance and the regulation of energy. Laboratory experiments, numerical and theoretical studies all provide information that contributes to safer exploitation of deep resources.
However, there is no unified research that addresses multivariate properties and the problems facing the safe exploitation of resources in the 21st century. There are also very few advances and innovations in mining theory. For this reason, challenges exist in resolving resource exploitation issues. A reform of mining methods based on rock mechanics is needed to address the critical issues facing the mining industry.
Current methods of long-cut mining
The long-cut mining method has been in use since the early 18th century, when it was developed in England. This method involves digging the coal across the width of the working face, removing the coal as it falls. Props are used to support the roof of the working face to prevent collapses. There have been tremendous changes in technology over the intervening centuries, but the basic idea is the same. Long-tailed mining removes a panel of coal, exploiting all available resources as the miners advance.
Historically, the 121 long blast mining method has been the most widely used method in the world since its invention. This method works on a face by digging two roads and reserving a pillar. Roads tend to get destroyed in this process due to extensive excavation work. The stresses are concentrated in the reserved pillar, causing severe deformations on the surrounding rocks, leading to potential catastrophes. The coal pillar also contains exploitable resources that must be left in situ For safety reasons.
Due to these problems, alternative methods have been proposed and implemented. These include Method 111 first proposed in the Soviet Union, which reduces excavation of roads and improves resource extraction, but still has pillar stress problems, and the theory of cutting of pillars. cantilever beams.
Analysis of the characteristics of the traditional method 121 Longwall
Several characteristics of the traditional method 121 have been studied for several years. They affect the safe operation of long-scale mining and their understanding informs developments in methods that improve this traditional mining technique.
The mining pressure law of the face is divided into five general stages: (Before the immediate collapse of the roof, the immediate collapse of the roof, collapse of the main roof, fracture and subsidence of the overlying strata and subsidence of the ground surface.
The characteristics of the pavement and the pillar are analyzed to understand the movement of the overlying strata and its mechanical state at different positions. The analysis process includes the force characteristics of the coal pillar, the law of motion of the overlying strata and the force state of the road support system.
Use of rock mechanics for proposed long-size excavation methods
A study published online in 2021 proposed long-scale mining methods based on advanced studies of rock mechanics. Updating current methods 121 and 111 will provide solutions to common problems. A key concept is to use the characteristics of rock mechanics to avoid excavation of the roadway and waste of resources. By using the mining pressure and the expansion characteristics of the collapsed rock mass, roads can be automatically formed.
The proposed advances include the short cantilever beam model and the equilibrium mining theory. In addition, methods 110 and N00 are proposed. Roof cutting and pressure release without the need for pillars are offered for automatic pavement formation. Key technologies offered include directional roof pre-cut technology, bidirectional energy cavity tension blasting techniques, constant resistance support technologies, and gangue blocking supports.
New mining methods have been applied in Chinese mines with different characteristics such as overburden, thickness of coal seams, roof types and gases. These field studies made it possible to create an integrated method of both supporting the pavement and operating the vein. Recent studies have shed light on the basis of a smart, unmanned development direction for mining.
This equilibrium mining model takes into account both the smart mining requirements of modern industry and the complex geometries of deep mines.
The future of mining rock mechanics
The proposed methods for achieving equilibrium mining have already been implemented in mines, including the Ningtiaota coal mine in western China. There are future prospects for long-cut mining which harnesses rock mechanics to achieve automated excavation of roads without the need for resource-rich pillars. These methods will enable the mining industry to achieve its goal of smart, automated, worker-less mining that dramatically improves miner and asset safety while reducing the costs associated with catastrophic mine failures.
Further reading and more information
Hualei, Z, Chen, Y & Zhije, W (2021) Special issue: Rock mechanics in deep mining engineering [online] Advances in civil engineering | Hindawi.com. Available at: https://www.hindawi.com/journals/ace/si/389502/
Him, M et al. (2021) Innovation and the future of mining rock mechanical [online] Journal of Rock Mechanics and Geotechnical Engineering 13 (1) p. 1-21 | sciencedirect.com. Available at: https://doi.org/10.1016/j.jrmge.2015.07.002