Alternative geostatistical analysis of the northern slope of the open pit mine "Ćirikovac" in the zone of the longitudinal profile n



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ГОДИШНИК НА МИННО-ГЕОЛОЖКИЯ УНИВЕРСИТЕТ “СВ. ИВАН РИЛСКИ”, Том 57, Св. II, Добив и преработка на минерални суровини, 2014

ANNUAL OF THE UNIVERSITY OF MINING AND GEOLOGY “ST. IVAN RILSKI”, Vol. 57, Part ІI, Mining and Mineral processing, 2014



ALTERNATIVE GEOSTATISTICAL ANALYSIS OF THE NORTHERN SLOPE OF THE OPEN PIT MINE "ĆIRIKOVAC" IN THE ZONE OF THE LONGITUDINAL PROFILE No. 8
Željko Praštalo, Dragan M. Milošević, Tanja Hafner - Ljubenović
RUDARSKI INSTITUT d.o.o. Beograd, 11080 Beograd, Batajnički put 2, Serbia, zeljko.prastalo@ribeograd.ac.rs
ABSTRACT. Following the suspension of works on the coal exploitation at the open pit mine Ćirikovac, a landslide occurred on the northern slope which slowed down the adaptation of this area into the fly and bottom ash disposal site aimed to receive the waste material form Kostolac Power Plants.

In order to provide the best possible technical solution for the accidental situation, where it was necessary to construct the retaining walls to repair the landslide by adding a weight to the foot of the slope, and to expand the area for disposing large quantities of ash, a stability analysis was performed and presented in this paper.


Keywords: OPM ĆIRIKOVAC, KOSTOLAC, LANDSLIDE, DISPOSAL SITE, FLY AND BOTTOM ASH, DISPOSAL, RETAINING WALL
АЛТЕРНАТИВЕН ГЕОСТАТИСТИЧЕСКИ АНАЛИЗ НА СЕВЕРНИЯ ОТКОС В ОТКРИТ РУДНИК „ЦИРИКОВАЧ” В ЗОНАТА НА НАДЛЪЖЕН ПРОФИЛ № 8

Желко Пращало, Драган М.Милошевич, Таня Хафнер – Любенович

РУДАРСКИ ИНСТИТУТ Белград, 11080 Белград, Батайнички път 2, Сърбия, zeljko.prastalo@ribeograd.ac.rs
РЕЗЮМЕ. След прекратяването на добива на въглища от открит рудник „Цириковач” се появява свлачище на северния откос, което забавя адаптирането на района за насипище за летливи и дънни пепели, което трябва да приема отпадъците от електроцентралите в Костолац. Докладът представя анализ на стабилитета, за да се осигури най-доброто техническо решение на възникналата ситуация, там, където е необходимо да се изградят подпорни стени за свлачището чрез добавяне на тежест в долната част на откоса и за разширяване на площта за депозиране на големи количества пепел.
Ключови думи: Открит рудник „Цириковач”, Костолац, свлачище, насипище, летливи и дънни пепели, изхвърляне, подпорна стена


Introduction
The geostatistical analysis of the northern slope of OPM "Ćirikovac" in the area of the profile No. 8 was performed due to emergence of two conflicting requirements during reassigning of the mining area into the disposal site for fly and bottom ash generated in the thermal power plant Kostolac.
After the landslide, it was necessary to add weight, aimed to rehabilitate the northern slope and prevent its further slippage, by constructing a retaining wall. This caused the reduction of landfill space, although the initial objective was to obtain the largest possible area for disposal of fly and bottom ash in the particular contour of former open pit mine. It is important to mention that profile No. 8 is selected because it is positioned in the central area of the mine where the greatest quantity of mass is present that affect the volatility of the said area.
Figure 1 presents the layout from May 2009, with the position of profile No. 8 (light blue), the contour of the landslide (orange) and the position of the partition embankment.
Description of the works on the PK "Ćirikovac" after termination of coal mining
Image, displayed in Figure 2, shows the status of the works at the end of coal exploitation.
At the end of coal exploitation at OPM "Ćirikovac", the lowest point at the foot of the northern slope was about +38 m, while the highest elevation of the terrain in the north central part of the affected top benches of the peak was around +160 m.
After termination of coal mining at OPM "Ćirikovac" (April of 2009.), the priority was to continue with works on the preparation and landscaping of the area for the construction and installation of facilities to be used for the ash disposal. In late April and early May of 2009, due to emerged landslide on the northern slope of the open pit (Figure 3 and 4), the works are intensified on the repair of the said landslide.
Following the initial release of the slide masses and performed survey, but prior preparation of the detailed design for permanent rehabilitation of the landslide, an embankment was constructed in the zone of the profile No. 8 in direction north-south. This was a primary measure to slow the progression of the sliding surface by wedging into the southern part of the open pit. The embankment was built with mining equipment, mainly Dragline EŠ 45/5, during 2010. In the first phase, the level of the embankment was + 48 m, which was later upgraded to the elevation of +58 m.
The embankment also has a role of transport communication path between the northern and southern part of the open pit.




Embankment in the foot of the slope in the yone of the porfile No. 8


Fig. 1. Contours of landslides with the position of profile No. 8 [6]






Fig. 2. Status of the works at the end of coal exploitation al OPM "Ćirikovac"  (April 2009) [5]

Fig. 3. Northern slope at OPM "Ćirikovac" after landslides (May 2009) [5]



Phased study of the stability of the northern slope before and after the construction of the retaining embankment at profile No. 8
For the calculation of stability the following geotechnical parameters were adopted = 11, C = 0 kN/m2 i y = 20.0 kN/m3.

The impact of water on the stability is taken using the pore pressure coefficient (0.0 - 0.3).

In order to check whether the original embankment contributed to improved stability, calculations were performed using block method before and after the construction of the embankment, and the resulting factors of safety are presented in Table 1.

Table 1. The resulting safety factors




ru

Fs

Situation 1

Situation 2

Situation 3

Situation 4

0.0

1.59

1.53

1.70

1.48

0.1

1.47

1.39

1.58

1.37

0.2

1.34

1.26

1.44

1.25

0.3

1.22

1.66

1.31

1.14

Projects, aimed to develop technical solutions to repair the occurred landslides, anticipate the construction of slopes with benches, as presented in the following figures (dark yellow color). Performed stability calculations included the final contour of the northern slope in the area of the profile No. 8 and the final projected height of the designed embankment at the foot of the slope at + 58 m.






Fig. 4. Profile No. 8 after landsliding (situation 1)

Fig. 5. Profile No. 8 with partition embankment set at the foot of the slope (situation 2)


Fig. 6. Profile No. 8 with projected state and the embankment at the foot of the slope up to level 58 + m (situation 3)



As the goal of these studies was to find optimal solutions for permanent stability of the northern slope, but also to leave more space in the final contour for the disposal of fly and bottom ash, figure 8 illustrates the contour of the slope where the terrain was presented with the initial height at the foot of the slope, ie. the vertical alignment of the terrain before the construction of the embankment.




Fig. 7. Profile No. 8 with projected condition and terrain with the initial height at the foot of the slope (situation 4)


It is important to note that investigation showed that its primarily purpose is transportation communication route between the two sides of the pit, and there is no significant impact on increased stability. As the disposed quantity of ash will rise, transport communications can be formed around the projected routes of the detailed mining project for permanent suspension of work at the open pit mine Ćirikovac - Kostolac", which is scheduled at the level +92 m, the function of the partition walls will slowly disappear and will not longer be used for this purpose. For this reason, it is possible, if it is necessary to expand the area for ash disposal, the existing embankment and mass incorporated can be used in the final stages of rehabilitation, light green in Figure 9.



Fig. 8. Profile No. 8 with projected state according to detailed mining project for permanent suspension of works at OPM "Ćirikovac" - Kostolac



Conclusion

Following the construction of the partition embankment at the foot of the northern slope the mass balance was partially established, especially when the embankment reached its maximum height. After that extreme break, the landslide at the northern slope was settled and it was able to intensify the rehabilitation works.



References

[1] Supplemental mining project permanent suspension of work on the open pit "Ćirikovac" - Kostolac, Book 2.1 Excavation and disposal of mine waste, Volume 2.1.2 Technical design of the waste transportation and disposal of technology, RI, 2011.

[2] Geological exploration works on the northern slope OPM Ćirikovac (Volume Ge.1 Additional mining project of thick ash hydromixture pipeline route to the excavated area at OPM Ćirikovac - Alternative south), RI, 2010.

[3] Geotechnical study of the conditions of the rehabilitation of landslides on the northern slope in the function of the formation of ash disposal site in the excavated area of the OPM Ćirikovac, RI, 2011.

[4] Simplified mining project of rehabilitation of landslides at the excavation front of the OPM Ćirikovac, RI, 2011.

[5] Photo archive, RI, 2008 - 2011.

[6] Simplified mining project of rehabilitation of landslides at the excavation front of the OPM "Ćirikovac" RI LTD, 2010.

Recommended for publication by Editorial board.





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