When mining depths in underground mines increase , so do the challenges . Therefore , an entirely new method has been developed – raise caving . This is a major groundbreaking step towards a safer , more efficient mine . “ Raise caving has been developed for efficient mining at great depth ,” says Matthias Wimmer , Section Manager in the Department of Mining Engineering at iron ore miner LKAB in Kiruna . Rock stresses increase as mining moves to ever greater depth . A more complex geometry , in combination with rockmechanical challenges , places demands on new , sustainable and innovative solutions for the mine of the future . And , underground , safety is paramount . “ Our exploration results are extremely promising and open the way for mining under our current main levels far into the future , beyond 2060 . But this also places demands on new technology , on solutions and methods that are adapted for new conditions ,” says Wimmer .
The greater mining depth has necessitated the development of the new method , raise caving . Both the method and the machine concept , which is an essential part of the mining method , have been developed by LKAB in close collaboration with Montanuniversität Leoben , in Austria . Large-scale testing will begin next year in the Kiruna mine . “ We still have a huge amount of work ahead of us . Two test areas will be developed : one for the machine concept and one for the mining method . Initially , individual components will be tested step-wise . Thereafter ,
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the complete system will be tested ,” explains
Wimmer .
The method currently applied in LKAB ’ s underground mines , large-scale sublevel caving , has been very successful . This is an effective method that enables mining of large volumes at a relatively low cost . However , there is some question as to how appropriate this method is for mining at ever greater depth . “ There are some mines with production at extreme depths , down to as much as 4,000 m . However , mines in which some form of large-scale caving is applied have not yet reached such depths . And there is a lot of uncertainty as to whether they can maintain viable production volumes in the longer term ,” says Wimmer . In other words , the application of caving methods at depth is largely unproven .
Raise caving , as opposed to sublevel caving , is a method that enables mining of the orebody from bottom to top , instead of from top to bottom . In other words , the sequence is reversed , and the technology shift has several advantages , not least in terms of safety . “ Rock stresses can never be eliminated in a mine but , with this method , we are able to determine where seismic events occur , far from the active infrastructure . This means that we allow events , but in specially predetermined places ,” explains Wimmer .
In addition , this “ upside-down ” method , in combination with good draw control , allows good conditions for mining more ore and significantly less waste rock , since dilution is avoided . But raise caving presents even more
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possibilities . “ Since the infrastructure and drifting , ie , developing roads in the mine , can be reduced , we have the prerequisites for improving efficiency by as much as 50 %.”
Raises are bored and that is the starting point for mining in slices and caving the ore from the bottom to top . This means that mining starts in the raises and is not done horizontally and conventionally by means of so-called drifts . This implies that no people work directly with drilling and blasting , in a conventional sense , within the raises . “ Concurrently with development of the raise caving method , we have worked with machine development . This is a highly automated machine that can both drill and charge via the raises . We are also developing a module for , among other tasks , rock reinforcement and hydraulic fracturing ,” says Wimmer . www . lkab . com ; www . unileoben . ac . at
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