A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ
A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ A OPEN PIT MINING AÇIK OCAK MADENCİLİĞİ
The tectonic activity involved an abrupt change of the phosphate layer’s dip (which was 15°) as it is presented in figure 2. Note that, with the progress of the mining works (excavation of slope toe) the abutment of the superimposed layers decreases and their dips increases; what influences negatively the stability. 3.1 Nature of the Landslide The landslide appears, at first sight, like a rotational slump (curved slip surface) but according to the geological cross-section (stratified formations) and the position of the surface of failure (the bedding plane between the Phosphate deposit and the Marl layer) the slid is classified as translational. The Phosphate layer, which is qualified hard rock, surmounts the Marl layer, which is qualified soft rock, from where the joint separating these two formations constitutes a favorable surface of slip. The basal friction in this case is favorable to the gravitating movements. Figure 2. Geologic cross-section of Kef Essenoun before the landslide. 3 LANDSLIDE OF THE KEF- ESSENOUN On September 8th, 2007, occurred the landslide of the north-eastern side of the pit (Figure 3). An important mass of rocks was detached from the rock mass filling the entire pit (the volume of the sliding mass is estimated at 6 000.000 m 3 ). Figure 4. The failure surface of the Kef Essenoun landslide. 3.2 Geotechnical Characteristics The rock formations Kef Essenoun are characterized by a very low, low to average resistance (according to the values of the Compressive strength) and according to their Poisson's ratios they are little consolidated rocks (the marl formation) and compacted rocks (the other formations). Figure 3. The landslide of Kef Essenoun open pit. 172
23 rd Table 1. Geotechnical characteristics of different rock formations. Properties Quaternary Limestone Phosphate Marl Uniaxial Compressive strength (MPa) Angle of internal friction (°) Rock cohesion (MPa) Specific gravity (KPa) Young's modulus (MPa) Poisson's ratio 19.17 58.84 22.55 21 25 40 37 15 1.96 8.24 7.35 1 18 25.5 22.55 20 5000 27000 24000 1000 0.32 0.25 0.28 0.40 3.3 Effect of Topography For the case of the landslide of Kef Essenoun, the sliding mass presents wrinkles resulting from the side spreading out. The effect of the topography on the mobility of the sliding mass is weak in this case. The effects of the seismicity and pluviometry are weak because this zone is arid and characterized by a weak seismic activity (Figure 5). Figure 6. Kef Essenoun open pit before the landslide The bench represented in red squares has a rather good stability and the safety factor is around 1.3, for a slope angle equalizes with 75°, for a critical condition of slope angle which exceeds the 80° the safety factor is around 1.0 (Figure 7). It is worth noted that the overall slope of the open pit is in a critical condition. But if the height and the angle of the bench are taken equal to 15 m and 55° successively with a bench width equal to 15 m there will be an overall slope of the pit characterized by 70 m height and an overall slope angle of 30° from where the safety factor will be higher than 2. Figure 5. Topographic constraint visualized by the form of the corridor of displacement 3.4 Effect of the Geometry The bench of Kef Essenoun open pit is characterized by 30 m height, an angle of slope of 75° and sometimes it exceeds the 80° and a bench width equal to 10 m (Figure 6). Figure 7. The safety factor according to the height and the angle of slope. 173
- Page 121 and 122: 23 rd every ore block and searches
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- Page 135 and 136: 23 rd 6 THE HIERARCHICAL PREFERENC
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- Page 149 and 150: 23 rd REFERENCES Alumur, S. A., &
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The tectonic activity involved an abrupt<br />
change of the phosphate layer’s dip (which<br />
was 15°) as it is presented in figure 2.<br />
Note that, with the progress of the mining<br />
works (excavation of slope toe) the abutment<br />
of the superimposed layers decreases and<br />
their dips increases; what influences<br />
negatively the stability.<br />
3.1 Nature of the Landslide<br />
The landslide appears, at first sight, like a<br />
rotational slump (curved slip surface) but<br />
according to the geological cross-section<br />
(stratified formations) and the position of the<br />
surface of failure (the bedding plane<br />
between the Phosphate deposit and the Marl<br />
layer) the slid is classified as translational.<br />
The Phosphate layer, which is qualified<br />
hard rock, surmounts the Marl layer, which<br />
is qualified soft rock, from where the joint<br />
separating these two formations constitutes a<br />
favorable surface of slip. The basal friction<br />
in this case is favorable to the gravitating<br />
movements.<br />
Figure 2. Geologic cross-section of Kef<br />
Essenoun before the landslide.<br />
3 LANDSLIDE OF THE KEF-<br />
ESSENOUN<br />
On September 8th, 2007, occurred the<br />
landslide of the north-eastern side of the pit<br />
(Figure 3). An important mass of rocks was<br />
detached from the rock mass filling the<br />
entire pit (the volume of the sliding mass is<br />
estimated at 6 000.000 m 3 ).<br />
Figure 4. The failure surface of the Kef<br />
Essenoun landslide.<br />
3.2 Geotechnical Characteristics<br />
The rock formations Kef Essenoun are<br />
characterized by a very low, low to average<br />
resistance (according to the values of the<br />
Compressive strength) and according to their<br />
Poisson's ratios they are little consolidated<br />
rocks (the marl formation) and compacted<br />
rocks (the other formations).<br />
Figure 3. The landslide of Kef Essenoun<br />
open pit.<br />
172
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