Opencast Highwall
Leonides Suttle
Surface mining makes up a huge percent of mining projects. Surface mining refers to the removal of the terrain surface to access minerals underneath. In particular, surface mining is used to retrieve sand, gravel, stones, coal, iron and other metals.
There are five recognized types of surface mining, each with specific variations depending on the minerals being extracted. These include strip mining, open-pit mining, mountaintop removal, dredging and highwall mining.
Surface mining is often the preference for mining companies. This is because removing the terrain surface, or overburden, to access the mineral beneath is often more cost-effective than gouging tunnels and subterranean shafts to access minerals underground.
Open-pit mining is similar to strip mining, except the ore is removed from an open pit which is not then filled in. Open-pit mining has been around for centuries, with ancient cultures like the Greeks, Romans, and Persians mining for granite, marble and even salt.
Mountaintop Removal Mining is highly controversial, and best suited for retrieving mass amounts of minerals, usually coal, from mountain peaks. The process involves blasting the overburden with explosives above the mineral seam to be mined. The broken mountaintop is then shifted into valleys and fills below.
An expensive and remotely controlled highwall mining machine excavates in a tight square from the face, using continuous drilling. Conveyor belts and pulleys move the matter from the drill through the device and the leftover matter is deposited behind the drill.
Coal has been recognized as the most important source of energy for electricity generation in India. Currently the country produces more than 550 million tonnes of coal per year, more than 80% of which comes from opencast mines. The demand of coal is increasing day by day. Despite of having the fourth largest coal reserve and being the third largest coal producing country in the world, India needs to import coal to meet its growing requirement. Most of the opencast coal mines were started in early eighties in India. Many of these opencast mines are reaching their pit limits. A significant amount of coal is blocked in non workable thin seams, in the highwalls, below surface dwellings in these opencast mines. Highwall mining is a proven technology in USA and Australia to extract the blocked coal in thin non-workable seams and the coal blocked in the highwall of opencast mines. In USA, highwall mining contributes about 4.0 % share of total coal production. In India, the highwall mining is in the nascent stage. So far only two highwall mining are being worked; one by Singreni Collieries Company Ltd at RG II opencast project and other by South Eastern Coalfields Ltd at Sharda opencast mine . Many projects have been identified by major coal producing companies like Coal India Ltd, Tata Steel and Singreni Collieries Company Ltd. for introduction of this technology. The future of highwall mining in India is keyed to the success of these projects. This paper gives an overview of the highwall mining technology deployed at Sharda opencast mine where two thin seams are being extracted by this technology.
Highwall mining is a hybrid form of mining that accesses coal reserves from the base of an exposed highwall. It is typically used when the surface mining operation reaches the economic limitation imposed by the stripping ratio.
Rockfalls in mines represent one of the most hazardous events for miners, posing significant risks to safety, equipment, and operations. These incidents occur when rock or debris falls from the walls of a mine, often without warning, and can be triggered by geological factors, blasting practices, ground vibration, water infiltration, stress redistribution and timedependent behaviour of rock. Apart from this, the bench parameters, such as the slope angle of the bench, the friction angle of the material, bench height and width, affect the rockfall. The rockfall incidents history that occurred in the past several years suggest that rockfalls in opencast mines led to the fatal injuries of many individuals. The problems faced due to rockfalls are not repetitive, but they are disastrous in opencast mines once they occur. So, it is necessary to investigate the rockfall in an opencast mining industry. It is also observed from the literature that the kinetic energy of a rockfall helps determine the intensity of rockfall in a mine. Understanding these factors and implementing preventive measures and rapid response strategies is crucial in mitigating rockfall risks. Hence, this study investigates rockfall phenomena in a high wall open cast by determining the kinetic energy of a rockfall. A parametric study has been conducted to determine the effect of various bench parameters on the kinetic energy of rockfall. A predictive model is developed to determine the kinetic energy of rockfall concerning various factors affecting rockfall. The predictive model is also validated using three case studies of high opencast mines. The results from the predictive model and the numerical model for the case study mines match the predictive model that can predict the rock fall intensity for opencast mines. The study also aims to assess the potential risks posed to workers, equipment, and infrastructure in highwall opencast mines. The findings provide valuable insights for implementing appropriate safety measures and developing effective strategies to mitigate rockfall hazards.
Labiouse V, Descoeudres F. Possibilities and difficulties in predicting rockfall trajectories. Joint Japan-Swiss scientific Seminar on impact load by rock falls and design of protection structures, Kanazawa; 1999.
Lee K, Elliott G. Rockfall: Application of computer simulation to design of preventive measures, planning, design and implementation of debris flow and rockfall hazards mitigation measures. Association of Geo- Technical Specialists and Hong Kong Institution of Engineers, Hong Kong; 1998.
Surface mining, including strip mining, open-pit mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit (the overburden) are removed, in contrast to underground mining, in which the overlying rock is left in place, and the mineral is removed through shafts or tunnels.
In North America, where the majority of surface coal mining occurs, this method began to be used in the mid-16th century[2] and is practiced throughout the world in the mining of many different minerals.[3] In North America, surface mining gained popularity throughout the 20th century, and surface mines now produce most of the coal mined in the United States.[4]
Advantages of surface mining include lower cost and greater safety compared to underground mining. Disadvantages include hazards to human health and the environment. Humans face a variety of health risks caused by mining such as different cardiovascular diseases, food, and water contamination. Habitat destruction, alongside air, noise, and water pollution, are all significant negative environmental impacts caused by the side effects of surface mining.
Strip mining is the practice of mining a seam of mineral, by first removing a long strip of overlying soil and rock (the overburden); this activity is also referred to as overburden removal. It is most commonly used to mine coal and lignite (brown coal). Strip mining is only practical when the ore body to be excavated is relatively near the surface and/or is mostly horizontal.[5] This type of mining uses some of the largest machines on earth, including bucket-wheel excavators which can move as much as 12,000 cubic meters (16,000 cu. yd.) of earth per hour.
There are two forms of strip mining. The more common method is area stripping, which is used on fairly flat terrain, to extract deposits over a large area. As each long strip is excavated, the overburden is placed in the excavation produced by the previous strip.
Contour mining involves removing the overburden above the mineral seam near an outcrop in hilly terrain, where the mineral outcrop usually follows the contour of the land. Contour stripping is often followed by auger mining into the hillside, to remove more of the mineral. This method commonly leaves behind terraces in mountainsides.
Open-pit mining refers to a method of extracting rock or minerals from the earth through their removal from an open pit or borrow. This process is done on the ground surface of the earth [6] It is best suited for accessing mostly vertical deposits of minerals. Although open-pit mining is sometimes mistakenly referred to as "strip mining", the two methods are different (see above).
Mountaintop removal mining (MTR) is a form of coal mining that mines coal seams beneath mountaintops by first removing the mountaintop overlying the coal seam. Explosives are used to break up the overburden (rock layers above the seam), which is then removed. The overburden is then dumped by haul trucks into fills in nearby hollows or valleys. MTR involves the mass restructuring of earth in order to reach coal seams as deep as 400 feet (120 m) below the surface. Mountaintop removal replaces the original steep landscape with a much flatter topography. Economic development attempts on reclaimed mine sites include prisons such the Big Sandy Federal Penitentiary in Martin County, Kentucky, small-town airports, golf courses such as Twisted Gun in Mingo County, West Virginia and Stonecrest Golf Course in Floyd County, Kentucky, as well as industrial scrubber sludge disposal sites, solid waste landfills, trailer parks, explosive manufacturers, and storage rental lockers.[7]
This method has been increasingly used in recent years in the Appalachian coal fields of West Virginia, Kentucky, Virginia, and Tennessee in the United States. The profound changes in topography and disturbance of pre-existing ecosystems have made mountaintop removal highly controversial.[8]
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