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Problems of land reclamation during liquidation of coalmining enterprises
To cite this article: G B Pospehov et al 2017 IOP Conf. Ser.: Earth Environ. Sci. 87 042015
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IPDME 2017 IOP Publishing
IOP Conf. Series: Earth and Environmental Science 87 (2017) 042015 doi :10.1088/1755-1315/87/4/042015
Problems of land reclamation during liquidation of coal-
mining enterprises
G B Pospehov, K V Pankratova, I A Straupnik, D L Ustiugov
Saint-Petersburg Mining University, 2, 21 line V.O., Saint-Petersburg, 199106, Russia
E-mail: pospehov@spmi.ru, pan-ksenia@yandex.ru, straupnik@rambler.ru,
ustiugov@mail.ru
Abstract. The paper presents data on the influence of coal-mining industry elimination on the
deformation of land surface which can cause accidents and destructions of buildings and
constructions located nearby the closed pits or mines. The analysis is carried out and the major
factors which influence change of the intense deformed condition of the massif of rocks were
revealed. The example of the monitoring system which will provide researchers with
information for preparation of the project of a pit or a mine closing is presented, and it also will
allow one to predict behavior of the massif in the future.
1. Introduction
The analysis of the actual costs of coal-mining restructuring needs has shown that elimination of
excavations in a total amount takes a small part (5.7%), and among other main expenses the highest
expenses is the cost of consequences mitigation after mining operations have been done (27.8%) [1].
At the beginning this circumstance was explained by the absence of scientific and technical
ensuring restructuring which has led to the fact that projects on closing mines and pits have not
considered prevention of harmful effects from conducting mining operations after their stop. But the
solution of environmental problems at liquidation of the coal enterprises has gained paramount value
[1, 2]. At the same time, as a rule, the most of the closed enterprises are situated on the territories with
a high degree of urbanization and are close to large settlements.
The analysis of such consequences shows that in the zones of the liquidated enterprises influence,
complex environmental problems appear in connection with change of the hydrogeological conditions
as a result of the returning of underground waters to the natural historical level which took place
before mining [2, 5].
Closing coal mines and pits with their transfer to "wet" preservation or water management
recultivation is followed by flooding of the developed space and restoration of underground waters
levels.
At the same time there is a flooding and bogging of territories, pollution of water intakes and
reservoirs, landslide processes become more active and the stress state of rock massif changes.
Development of landslide processes in borders of subsidence troughs near the flooded
“Capitalnaya” mine (The Kuznetsk basin) has caused, due to displacement of covering deposits from 2
to 8 meters in depth, damage of houses in the town called Osinniki that demands at the moment
resettlement of 3 thousand inhabitants [4]. The similar situation has developed also to Karpinsk [6].
Many of negative and dangerous processes at the liquidated enterprises do not prove themselves
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IOP Conf. Series: Earth and Environmental Science 87 (2017) 042015 doi :10.1088/1755-1315/87/4/042015
instantly but only months and years later. That is why the majority of such processes are difficult to
predict.
Only in the period of 1998-2000, to solve these problems various organizations have performed
more than 120 research works connected with ecological aspects of mines and pits elimination. On
their basis, a number of the normative documents have been created. They are designed to regulate an
order of technical works performance during the liquidation of the coal-mining enterprises and
compliance with the ecological standards in a zone of their influence [2, 3].
The majority of researches were carried out for underground coal-mining which prevails among the
closed enterprises. However, on the operating open-cast mining in general there are the same
processes as on underground one. They are: the continuous deterioration in development conditions
and increase in capital investments [4]. It allows one to expect further increase in quantity of the
closed coal pits, but insufficiently detailed studying of negative aspects of such actions can lead to
very dangerous ecological consequences.
At the same time in Russia a transition from an underground way of coal mining to more effective
– open one is systematically carried out (fig. 1). During 1993-2003, the number of the operating coal
mines was reduced from 231 down to 95, and the number of pits has increased from 65 up to 121 [8].
Now in the coal industry of Russia 241 coal-mining enterprises are operating and they are 104 mines
and 137 pits [6]. In the general production, the share of the open way will increase up to 70-75% and,
by some estimates, it will make 80-85% by 2020 [4, 7, 9]. There is an increase in a share of an open
way of coal fields developing in some other countries too. For example, the share of open-pit coal-
mining is: in Australia – 67%, in Canada – 90% (Kirukov V V 1997).
Figure 1.
The changes of the open way share in the general coal mining in Russia [4].
The prospects of coal-mining branch development in our country are defined by "The energy
strategy of Russia for the period till 2020" according to which coal mining in 2020 will increase up to
430 million tons.
So large coal reserves in bowels of Russia will be the main power raw materials and will have a
strategic importance. This circumstance assumes that in the future an intensification of coal fields
development in the country and the open way of production will prevail.
2. Practical example
At the end of the last century, the main reserves of coal provided by the project on the pit "Youzhny"
have been extracted. This pit is the main field for output of brown coals in Northern Urals. Mining
operations were performed behind technical border (working off of off-balance stocks) with use of
technology of filling the developed space. That is why the shareholders have made the decision on
elimination of a pit "Youzhny" with the natural flooding of residual excavations during the accepted
water management direction of recultivation.
The deposit is dated from the Mesozoic complex presented by thickness of the interstratifying
soapstones, aleurolites, sandstones, conglomerates, clays and coals with a general thickness about 300
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m. At the time of working off completion the pit was a ditch with the area of 15 sq.km and more than
200 m in depth with tilt angles of boards 15-20 degrees. The western non-working board was loaded
with the internal dumps created under corners of a natural slope. The east working board characterized
by a tilt angle 15-20 degrees and 180 m height. It was located near industrial and civil buildings of
Karpinsk.
During coal mining on the boards of the pit, there were problems with stability which were solved
by application of drainage by vertical wells. The elimination of the pit has led to the termination of
drainage works and the rock massif which have been drained was flooded that has affected
deterioration in boards stability conditions. That is why, on the east board of the pit the action against
landslide have been executed with use of a load of the local slope (fig. 2) with an overburden rock
mass (4.5 million m
3
).
A control of the boards stability have been doing by the means of a hydrogeomechanical processes
monitoring, which includes surveying of the board deformations on 5 profile lines and change of
underground waters pressures on 8 observation wells equipped with sensors of pore pressure at various
depths of the studied rock mass of Mesozoic and Paleozoic age.
Figure 2.
A schematic geological section of the east board of the pit "Youzhny" near the observation
line No. 8: 1 – limestone; 2 – breccia clay; 3 – bauxitic clay; 4 – conglomerates; 5 – soapstone; 6 –
sandstone; 7 – coal; 8 – dumps; 9 – explosive violations; 10 – observant reference point and their
number; 11 – water levels in career in June 2003 (+108 m) and in the end of the flooding (+179 m); 12
– territories of bakery (I) and milk plant (II); 13 – the observation well 3vn with sensors of pore
pressure.
The stationary regime observations have allowed one to record landslide deformations on local
sites of the board and raising of the land surface in the territory adjacent to the pit where buildings and
constructions of different function are located (Bakery, Milk plant, the power line, a collector, etc.).
The facts of the surface raising caused by the growth underground waters pressures due to flooding
have appeared because of recently coal mines closing. The flooding of the pit of such scale in Russia
is carried out for the first time. The results of the vertical shifts observations with the base stations put
on east board of the pit "Youzhny" are given in fig. 3. Rise in water level in the pit during the executed
observations has made 12 meters. The raising of the land surface between reference points No. 6 and
No. 13 (fig. 3) is caused by the rock massif stress state change at increase in underground waters
pressures drained earlier. It has predetermined a possibility of elastic deconsolidation of rocks and, as
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IOP Conf. Series: Earth and Environmental Science 87 (2017) 042015 doi :10.1088/1755-1315/87/4/042015
a result, a raising of the land surface.
At the same time in the pit boards on sites of a limestone’s exit to a day surface (or under
quaternary deposits), the land surface raising is observed. Within terrigenous thickness both
deformations are fixed: the raising one and the subsidence deformations caused by the shear plastic
shifts determined by features of a rocks bedding growing on contacts on local sites of the pit board.
The problems of negative consequences of coal pit flooding can be considered in two aspects.
On the one hand, the changes of the hydrogeological conditions can cause decrease in degree of
rocks stability at the boards of the pit and it can become the reason of deformations development at the
boards, ledges and adjacent sites of the land surface within width of a possible sliding prism, creating
a threat of various buildings and constructions safety.
On the other hand, the rise in water level and restoration of underground waters pressure in the
adjacent territory can lead to deformation of the land surface in the territory of former drinage.
Therefore, the forecast of flooding consequences during water management recultivation comes
down to the forecast of two gravitational geoengineering processes development: landslides of the
boards and ledges and deformations of the land surface in adjacent territories.
In generaly, stability of the east board of the pit "Youzhny" is provided with stability margin
coefficient not less than 1.3. At the same time it is possible the appearance of the local deformations
on the certain sites of the board.
Calculation of the land surface deformations as a result of the section flooding has shown that
because of underground water level rising in the pit, uneven positive shifts (raisings) on the land
surface are possible, with the maximum vertical deformations up to 13 cm at a distance of about 230
m from the pit border.
Figure 3
. Vertical deformations of reference points on the observation line No. 8 between 7 and 1
series (804 days).
3. Conclusions
Large coal reserves in bowels of Russia will be the main power raw materials. It is possible to assume
that there will be an intensification of coal fields development. At the same time, transition from an
underground way of coal mining to an open one is carried out systematically in Russia. In the general
production, the share of the open way will increase up to 70-75% and, by some estimates, it will make
80-85% by 2020. It means that scales of impact from mining on the environment will increase; in
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IOP Conf. Series: Earth and Environmental Science 87 (2017) 042015 doi :10.1088/1755-1315/87/4/042015
particular, the areas of the broken lands will increase rapidly.
The Russia’s coal industry large-scale elimination of unprofitable and unpromising coal mines and
pits has revealed some problems. During closing of the mining enterprises, besides an ecological
situation improvement, there is also an activization and emergence of the new dangerous geological
processes and the phenomena capable to affect geoengineering conditions of the former coal deposits’
territories.
Relevance of land reclamation problems is caused by urgent need in ecological safety ensuring in
territories of open mining operations even when they are ended. Also there is need in fastest and safe
development of the broken lands which are situated, as a rule, in densely populated areas (regions).
The scientific and methodical principles of geoengineering ensuring during elimination of the
mineral deposits excavations developed using the open cast mining are at an insufficient level today. It
is necessary to perform special researches for studying geoengineering conditions to be able make a
forecast of their change as a result of the remediation works. One of the tools which can provide
sufficient information is a monitoring based on geological processes developing models.
The system of geoengineering ensuring during the open cast minings elimination has to include:
studying and an assessment of geoengineering conditions, the forecast of these conditions changes
under the influence of the reasonably chosen direction of recultivation and the local geodynamic
monitoring of conditions’ changes which has to be carried out throughout recultivation of the pits.
The general hydrogeomechanical model of an object (a pit, the site of a board, the adjacent
territory, etc.) has to be a basis of the geoengineering estimates and forecasts received within
organized system of geoengineering during liquidation of the open cast coal-minings. This system can
be divided into several models depending on the arising and developing geological processes and
phenomena.
The water management recultivation of the pits is followed by change of geoengineering conditions
of the rock massifs and territories adjacent to excavations that affects the general geodynamic situation
of the area, provoking development of dangerous geoengineering, such as landslides and raising of the
land surface.
References
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[4] Grin’ko N K 2000 RUSSIAN COAL JOURNAL 11 7-12
[5] Zaidenvarg V E, Navitniy A M, Tverdochlebov V F 1999 RUSSIAN COAL JOURNAL 12 28-30
[6] Kutepova N A, Kutepov J I, Pospehov G B 2007 Oil 1 253-258
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