Unconventional support assessment for mines in sedimentary bedrock - Applicability of rock classification systems in horizontally bedded sandstone
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Examensarbete för masterexamen
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Coal mining has been a huge industry ever since the industrial revolution but has
in more recent years started to be phased out as renewable energy sources have
been further prioritised by our society. In order to not let the vast knowledge
and experience of the coal mining industry fade, this study seeks to evaluate the
applicability of Coal Mine Roof Rating, CMRR, in other settings. The assessment of
the classification system is performed through a comparison to Rock Mass Rating,
RMR. Both systems are evaluated through a case study of the Kvarntorp mine,
a sedimentary sandstone mine in Sweden. The mine has been excavated through
room and pillar mining, resulting in horizontal rooms with pillars of rock between
them. The geological properties of the bedrock were partly gathered from older
investigations from the mine and partly through extrapolations and estimations
based on properties of rock in similar conditions. The Geological strength index, GSI,
along with the Generalized Hoek-Brown failure criterion was utilised to characterize
the rock quality.
Two-dimensional finite element analysis was utilised to assess the system numerically.
Two models with differing approaches to evaluate joint sets and weakness
zones were created in the software RS2. The models were used to assess the stability
of 13 different scenarios, covering both the different classification systems and
the prospect of heightening the roof of the mine.
The behaviour of the two model types was very similar, showing no major discrepancies.
Their output indicates that the support recommendations from the classification
systems don’t affect the vertical displacement of the roof or the general
behaviour of the model. However, the roof suffers from yielded elements and bolting
is necessary to control these loose blocks. The CMRR support recommendation is
deemed to be the most efficient alternative in the Kvarntorp mine but it requires
thorough assessment of any weakness zones in the mine. If the weakness zones are
hard to assess, the RMR support recommendation is deemed the safer alternative
even though it is potentially too conservative. As the study was only conducted for
the one case of Kvarntorp, these findings are not directly applicable in other settings
but may instead be considered
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Ämne/nyckelord
support recommendation, bolting, Kvarntorp mine, coal mine roof rating, rock mass rating, sedimentary sandstone, room and pillar mining, geological strength index, generalized Hoek- Brown failure criterion, finite element analysis, RS2