ISSN 1062-7391, Journal of Mining Science, 2012, Vol. 48, No. 1, pp. 154-166. © Pleiades Publishing, Ltd., 2012.
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Raw Material Homogenization Production Plan in Multiple Quarries—Slope Stability Assessment: Cement Raw Material Clay Pit Sample1 D. Karakus Engineering Faculty, Department of Mining Engineering, Dokuz Eylul University, Buca-Izmir, Turkey e-mail:
[email protected] Received November 26, 2010
Abstract—Up-to-date solution algorithms, which are used to determine optimum production sequences and ultimate pit limits are discussed. These private solutions for quarries might be inadequate for different mining areas. Optimization solutions that are offered for quarries in raw material preparation process within constraints, which are determined by mixing raw material that were produced from different quarries such as cement production, fall short, instead these are replaced by trial and error methods that are made for main constraints. In this study, production sequence homogenization study for limestone that belongs to a cement factory and clinker production from two clay pits were presented, slope stability assessment was also made. As a result of these studies, a planning process based on production amounts, distances, chemical content of clinker and slope safety constraints was developed. Keywords: cement raw materials, mine planning, production scheduling, slope stability
INTRODUCTION 1
Traditional mining production planning is generally categorized as energy raw materials, industrial raw materials and metallic mining. Although they all have idiosyncratic characteristics, extracting economic mineral from bedrock by using mining techniques is their common characteristic. For instance, mining techniques by taking the strata mechanics and stratification process into account are used to determine the coal mining production techniques, in which the formation of coal exhibits sedimentary bedding. In this sense, production plans by taking heavy construction equipments such as draglines into account are made. On the other hand, relatively small capacity excavators are generally used for metallic mines, which exhibit mass and thin veined bedding type. When underground mining is considered, it anticipates production methods, in which bedding type is totally different. For instance, while longwall methods are preferred for stratified structures, on the other hand, sublevel and backfill systems are considered for mass and thin veined metallic mines. This general perspective indicates that production planning techniques in mining can be diverse. Other than that, another mining activity is the preparation study of an end product of a raw material, such as cement production. In this type of mining activities, as different from other mining activities, raw materials, which have different contents and were obtained from different quarries, are mixed and the main composition of end product is prepared. Miller made pioneering studies related to the importance of cement raw material procurement in quality allocation of raw material quarries [1]. In Luster’s study, it was emphasized that cement raw material procurement is decided with average chemical content values in quarries and this might be inadequate, then he emphasized the significance of vertical quality of raw materials in quarries. In his simulation study, he developed the algorithm for raw material procurement according to vertical quality differentiation. These studies were developed for limestone—the main raw material of cement—quarries and single quarries [2]. Similar studies were also made by Asad [3], who modeled 1
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short term production plans in limestone quarries for cement production by using linear programming algorithms. These simulation and linear programming algorithms, which are recommended as an alternative to trial and error method, were developed for single quarries by taking a lot of variables into account and solution recommendations were presented [4—6]. On the other hand, pit limit optimization for single quarries was made by Lerchs—Grossman with the implementation of dynamic programming and graph theory into block model [7]. Another study, which was intended for solving the problem, was the floating cone method that was developed by Pana [8]. This study is based on the movement of an inverted cone, which represents quarry slope, on blocks and the maximization of the sum of blocks’ economic value [9]. Meyer sought a solution to pit limit problem in open pit mines by using linear programming techniques but it was reported that Meyer’s method cause errors in ultimate pit limit determination [10]. The maximum flow algorithm was rapidly and successfully applied by Yegulalp and Arias in order to solve the problem, however Lerchs—Grossman algorithm, which was developed for the solution of the problem, is the most applied method [11]. Production sequence optimization is tried to be solved in the sequence, in which the net profit is maximum. In this sense, a solution was sought for this problem by applying operational research techniques and heuristic approaches [9]. At this juncture, the algorithms, which solve block extraction sequence and pit limit optimization simultaneously, and genetic algorithm approaches still keep their complexities and prominence as a specific field. In this study, the homogenization study, which includes many constraints and was made from more than one quarry, and production sequence are presented for cement raw material procurement. 1. MATERIAL
In this study, production sequence and optimization from raw material quarries, which belong to Soke Cement Factory that located in the Western part of Turkey, were evaluated. The main constituent of cement production is clinker, which is formed from a mixture of limestone with appropriate chemical content and clay. The chemical contents of raw material of clay and limestone, which form clinker, directly affect the quality of cement that is produced. In this sense, CaO, SiO2, Al2O3 and FeO3 compounds in limestone play an important role in clinker production. Moreover, some modules, which are used and based on chemical contents, were developed in cement industry. Silicate module, one of these modules, is one of the values that constraints raw material quality. Another constraint factor is MgO% ratio in cement. If MgO% ratio within cement is 2.5% in clinker, then appropriate quality cement can be produced. Appropriate raw material homogenization studies were made by taking production amounts into consideration with respect to limestone, which belongs to the factory, and constraint chemical contents that are determined from the clay pits. Location of the factory quarries and their distances are presented in Fig. 1. Consequently, Cankurtaran limestone quarry will be used for limestone procurement to the factory and Fevzipasa and/or Maliye clay pits will be used for clay procurement.
Fig. 1. Locations of the cement factory and the raw material quarries (not scaled). JOURNAL OF MINING SCIENCE Vol. 48 No. 1 2012
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Raw material homogenization study that will be provided with two clay quarries and one limestone quarry for the factory cement production is not only a linear optimization problem, which can be programmed with distances and production amounts. Raw material quality in quarries and its chemical content also directly affects clinker quality. On the other hand, production sequence and ultimate pit limit algorithms, which are developed for single quarries, can fall short in these kinds of situations because of plurality of variables. The distance of transportation routes, production amounts, vertical quality change of raw material alongside with stock area capacity of the factory and appropriate slope stability of quarries are the main constraint factors to determine raw material homogenization. Another important point to mention is the optimum realization of raw material mixture in quarries without stripping. For instance, limestone and clay with high MgO% contents shouldn’t be mixed. In this case, limestone with high MgO% content must either be kept in stock area, so reloading and transportation can be considered or it can be thrown in the dumping site as stripping. Basically, raw material homogenization was realized by taking following parameters into consideration for the studied area. 1. Annual 1 Mt/year limestone need of the cement factory and annual 250 000 tons/year limestone need of the ready-mixed concrete facility must be fulfilled from Cankurtaran area. Altitudes between +490 and +360 were planned in accordance with open pit mining technique by starting from the highest elevation in such a way that 10 meters scales will be built. Total limestone reserve was calculated as 51 829 265 tons with respect to formed production plan. 2. Although Maliye clay pit is more suitable with its low MgO% content than Fevzipasa clay pit, Fevzipasa clay pit is closer to the factory. Clays that reach up to 2.4 silicate module limit were identified as black clay and other clays that are above this value were identified as yellow clay. The production plan in Maliye clay pit is at altitudes between +75 and +185. Total 7 261 741 tons clay, which consist 5 358 949.4 tons yellow clay and 1 902 791.8 tons black clay, is available on the area between those altitudes. 3. Fevzipasa clay pit is the one that is closer to the factory and vertical quality of raw material in this basin has been increasing. In short term, Fevzipasa clay pit should be mixed with limestone with low MgO% content because it has high MgO% content. The production plan in Fevzipasa clay pit is at altitudes between +60 and +180. Total 19 705 772 tons usable quality clay, which consist of 3 083 678 tons yellow clay and 16 622 094 tons black clay, is available between those altitudes. MgO content of this clay varies from 5 to 8% and its silicate module (SM) varies from 2.0 to 3.6. 4. The mixture of limestone with low MgO% content, which will be produced in Cankurtaran limestone pit in short term, and clay with high MgO% content, which will be produced in Fevzipasa clay pit in short term, are more appropriate for raw material optimization. 5. In this sense, the mixture of limestone that was obtained from Cankurtaran limestone pit with clay that was obtained from Fevzipasa clay pit will provide appropriate clinker mixture and stocking will not be required. When those factors are taken into consideration, Fevzipasa clay pit has been determined as the quarry that will provide clay in short and medium terms with respect to transportation distances and ultimate raw material homogenization by especially taking limestone pit’s limestone quality with variable chemical content into account. Another essential factor in determining criteria is the determination of production sequence in terms of mining technique. It is essential that the material, which is excavated by mining activity, is directly used for clinker production. Quality allocation in quarries should be correctly determined with the formation of appropriate clinker mixture and appropriate mining technique in order to use selective excavation, which keeps quarry formation intact. JOURNAL OF MINING SCIENCE Vol. 48 No. 1 2012
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Fig. 2. Stratigraphic section, which shows deposits in Fevzipasa clay basin and its surroundings [12].
3. GEOLOGY
In the study area, two separate rock groups, which were formed during different periods, are being observed. Menderes massif’s various composition of schistose and marble with recrystallized limestones on top of them and young sediment group above these limestones with volcanic rocks, which cut all sequences, form the rock groups in the region. This area, which is located between two horsts and is surrounded with normal faults, consists old Neogene terrestrial and lacustrine sequences, which were formed by transitive lithologies. These sequences have similar and distinct lithostratigraphies at the same time and it indicates that lithostratigraphic units are discordant in time JOURNAL OF MINING SCIENCE Vol. 48 No. 1 2012
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and location. These sequences were divided in levels that were in discordance with each other and they separated into eight different transitive units within themselves. Generalized stratigraphic section of the area is presented in Fig. 2. The claystone unit, which belongs to Fevzipasa clay pit Neogene second sequence, surfaced. The bottom of this claystone unit consists of blackish-grey organic material (peat), which disintegrated from place to place, and high content claystone and siltstone. On top of it, greyish black limestone (black clay) and glass-shaped disintegrated yellow-black clay follows and on its top, it ends with yellow-gray clay. Fine and middle grained sand levels can be seen above clay sequence. In upper layers, sand levels turned into gravel dominated levels. Claystone unit, which approximately extends from west to east, moves to the north with a low slope (<%10) [12]. Sequence contains different levels as a chemical composition. In other words, SiO2 ratio of blackish-grey organic claystone and siltstone levels, which are observed at the bottom of quarry, are lower than desired value, on the other hand, MgO ratio is higher. Yellow clay and fine sands can be seen towards the top of sequence and at these levels, SiO2 ratio increases relatively. This situation exactly continues along the east-west direction in all Fevzipasa clay basin. 4. QUALITY MODELING OF FEVZIPASA CLAY PIT
First of all, raw material quality in basins needs to be determined in raw material mixture optimization studies. In this sense, quality allocation with respect to silicate module and MgO% allocation, which is essential for clay basins, were determined. Total 675 data were obtained from Fevzipasa clay basin, which is approximately 4.2 km away from the factory, by drilling 21 locations and conducting vertical analyses. An assessment was made, in which usable clay and waste material analysis with respect to essential MgO% contents for clinker production was conducted and silicate module (SM), in which yellow and black clay distinction analysis was made. Clay and stripping analysis in Fevzipasa clay basin according to 8% MgO ratio was conducted in order to keep the desired MgO% ratio in clinker because MgO% ratio of limestone in especially southern part of limestone basin was high. Any material that comprises MgO above 8% will be removed as stripping. Yellow and black clay distinction analysis was conducted according to 2.4 SM limit. Figure 3 shows MgO% contents and silicate module allocations for usable clay as a result of general statistical evaluation of Fevzipasa clay basin. In order to determine vertical position of clay in current basin, statistical analyses as horizontal slices in 10 meters distances were conducted in accordance with quarry production plans and the results are presented in Table 1.
Fig. 3. General statistical evaluation: (a) statistical evaluation for MgO% content, (b) statistical evaluation for silicate module SM. JOURNAL OF MINING SCIENCE Vol. 48 No. 1 2012
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Table 1. Usable clay quality values in different altitudes Black Clay MgO%
Bench, m
Yellow Clay
SM
X
SD
X
SD
140-150
6.69
0.51
2.12
0.08
130-140
6.48
0.85
2.16
120-130
6.68
1.07
110-120
6.73
100-110
N
MgO%
SM
N
X
SD
X
SD
5
5.38
1.59
2.85
0.24
5
0.14
15
5.74
0.95
2.92
0.61
10
2.08
0.11
42
6.26
1.17
3.84
1.77
6
0.93
2.05
0.11
53
4.78
1.39
3.28
1.10
9
6.34
1.01
2.07
0.15
65
5.58
0.48
2.63
0.15
7
90-100
5.64
1.19
2.02
0.14
92
5.05
0.60
2.46
0.04
2
80-90
5.29
1.18
2.03
0.12
96
-
-
-
-
-
70-80
5.57
1.11
2.03
0.13
65
-
-
-
-
-
60-70
5.34
1.00
1.99
0.10
32
-
-
-
-
-
50-60
4.67
1.13
1.97
0.10
6
-
-
-
-
-
X—Average; SD—Standard deviation; N—Number of sample
Fig. 4. Variogram model of Fevzipasa clay basin: (a) Variogram model for MgO content; (b) variogram model for silicate module [13].
Experimental variogram analysis was conducted by using drilling data. As a result of this analysis, no anisotropy was observed. Yellow and black clay were found as sequenced in a position close to horizontal in basin and according to variogram graphs that are presented in Figs. 4a and 4b, the correlation coefficient was as R = 0.773 for silicate module and R = 0.750 for MgO content [13]. As a result of those modeling studies, usable quality clay between +60 m and +140 m altitudes was found and quality allocation of basin that was based on obtained data was presented in Fig. 5. For MgO content: h = 110 m; C0 = 5; C = 24 nugget and spherical model. For Silicate Module: h = 185 m; C0 = 0.02; C = 0.12 nugget and spherical model.
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Fig. 5. Fevzipasa clay quarry quality modeling: (a) current situation of quarry; (b) eventual situation of quarry; (c) block model that was formed with respect to silicate module(SM); (d) block model cross-section image.
5. MINE PLANNING AND SCHEDULING
As a result of quality evaluation and reserve estimates, it was determined that yellow and black clay, which is required for the factory, can be produced from Fevzipasa clay basin. For this purpose, a production planning was made in such a way that MgO ratio in clinker will not rise above 4%. As a result of quality evaluation and basin modeling, it was determined that raw material quality in terms of MgO% content increased while descending to lower altitudes. In the light of this information, a planning was made in a manner that higher altitudes, where MgO% ratio was high, will be produced together with areas where MgO% ratio was low (0.5-1.0%). In the same way, an excavation program was prepared in a manner that lowers altitudes (+60, +70, +80), where MgO% ratio was low, will be produced in accordance with areas where MgO% ratio was higher in limestone basin. In addition to quality allocations in production planning, excavation sequence, which will provide optimum production, was taken into consideration. Coordinated production of yellow and black clays that are needed by the factory became the main goal. The stratigraphic sequencing of Fevzipasa clay basin is ranged from the top layer to bottom as stripping, yellow clay and black clay. A production planning was made, which fulfills black clay requirement of the factory and makes stocking of yellow clay, which is found above black clay and is used less in comparison with black clay, unnecessary. 5.1. Short and Medium Term Product Plan—Slope Stability Assessment
Besides a lot of other factors, safety must be taken into account to fulfill determined production amounts during raw material production from multiple quarries. In this sense, first of all, shear tests were applied to determine the internal parameters of clay in the basin on drilling cores that were obtained from drilling. The results of the test that was made with distinction analysis between yellow clay—black clay are given in Table 2. According to these results, as a result of shear box test for black clay, it was found that the internal friction angle was 39.00º and cohesion was 1.87 kg/cm2 and for yellow clay, internal angle was 39.69º and cohesion was 0.62 kg/cm2 (Fig. 6). JOURNAL OF MINING SCIENCE Vol. 48 No. 1 2012
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Annual clay consumption of the factory is 300 000 tons/year black clay and 100 000 tons/year yellow clay. It is necessary for this clay to have appropriate chemical content as amount and when it is mixed with limestone, it needs to provide appropriate clinker mixture. When quality values of the basin are taken into consideration, on a yearly basis, short time raw material production sequence of clay basin for the first five years was determined (Fig. 7). Here, the main factor that needs to be considered is the limestone basin and the chemical content of clinker, which was formed as a result of aforementioned mixture. For this reason, selective excavation method needs to be used. It was determined that high quality clay of the clay basin was found at lower altitudes. However, making production from lower altitudes might create negative circumstances in terms of quarry slope safety. Limit equilibrium slope stability analyses were conducted for short term production plans by taking slope safety into account. In limit equilibrium slope stability analyses, which were conducted by looking current situation of the quarry by the end of the year on a yearly basis, inner parameters that were determined for yellow and black clay were used and cross-sections were evaluated by taking them from the most risky areas of the quarry (Fig. 8).
Fig. 6. Black and yellow clay shearing strength diagram.
Table 2. Digital shear box test results for yellow and black clay Black clay
Yellow clay
Sample no.
Normal load, kg
Horizontal load, kg
Normal stress, kg/cm2
Shear stress, kg/cm2
Normal load, kg
Horizontal load, kg
Normal stress, kg/cm2
Shear stress, kg/cm2
1
10
65.22
0.33
2.18
20
34.46
0.67
1.15
2
20
59.73
0.67
1.99
30
33.23
1.00
1.10
3
30
89.38
1.02
3.04
40
64.26
1.33
2.14
4
40
94.60
1.34
3.18
50
63.02
1.70
2.14
5
60
98.17
2.01
3.30
80
81.42
2.68
2.73
Natural unit weight
2.04
1.98
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Fig. 7. Short term production sequence: (a) production sequence plan for the first five years; (b) cross-section.
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Fig. 8. Short term production plan—slope stability assessment.
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Revisable raw material production prospecting in medium term was made after coordinated planning phases of multiple quarries and short term raw material homogenization. Medium term production plan, which consists five year periods, was actualized by taking clinker production that will fulfill the factory’s needs and production sequence of quarries into consideration. In addition to required clay amounts for clinker, safe slope angles should be evaluated when quarry safety is considered. In this respect, limit equilibrium slope stability analyses were conducted in terms of geometric shape of the quarry that will be formed at the end of five year periods (Fig. 9). Obtained results are given in Table 3. According to general evaluation, Fevzipasa clay basin will work with average F = 3.78 safety coefficient in short and medium terms in terms of slope safety. 6. CONCLUSIONS
Optimization studies, which were made to gain maximum profit from single quarries in terms of reserve and tenor, can fall short in multiple quarries. Many restrictive factors in material procurement from more than one quarry and in raw material preparation practices, which were realized with mixture of multiple raw materials such as cement production, should be considered together. In addition to the chemical content of clinker, which is formed as a result of mixture, distances of multiple quarries, vertical variation of raw material in quarries and stock area capacity, another essential factor in terms of mining technique is slope safety of quarries. Unplanned short term productions from multiple quarries can cause problems in slope safety of quarries after a while. For this reason, vertical quality allocation of quarries, in which raw material is provided, must be determined thoroughly and production sequence must be done by taking this quality allocation into account. In this study, production sequence planning phases were identified by evaluating quality allocations of one limestone pit and two clay pits, which belong to a cement factory, and in addition to many other constraint factors, the significance of quarry planning was emphasized in terms of slope safety. As a general approach, production planning phases of multiple quarries are as follows: Determination of annual production amounts; Determination of possible quarries that can fulfill these production amounts; Determination of unit transportation costs according to distances; Determination of chemical content values that are formed as a result of raw material mixture; Determination of vertical allocation of raw material quality in quarries; Determination of appropriate scale sizes in terms of mining technique; Planning of coordinated production from multiple quarries; Possibilities of raw material mixture preparation without needing stock; Quarry safety and slope stability during raw material homogenization production studies. Linear optimization techniques or optimization techniques that are recommended for single quarries can be used by evaluating constraints in some of aforementioned phases. However, clinker production optimization from multiple quarries that comprises safe mining activities and all constraints can be illusory. Instead, short term production plans, which are conventionally prepared with minimized fundamental constraints, become more realistic and more applicable. JOURNAL OF MINING SCIENCE Vol. 48 No. 1 2012
RAW MATERIAL HOMOGENIZATION PRODUCTION PLAN IN MULTIPLE QUARRIES Table 3. Product amounts and safety coefficient of slope Period
Product amount of black
Product
amount
clay, t
yellow clay, t
of
Factor of safety for risky slope
First year
384222
122786
3.607
Second year
315470
107318
3.707
Third year
302500
112642
4.038
Fourth year
308830
106558
4.091
Fifth year
315336
77324
4.466
Tenth year
1626358
526628
3.194
Fifteenth year
1507746
398486
3.619
Twentieth year
1526356
526 678
3.348
Average
3.78
Fig. 9. Middle term production plan—slope stability assessment.
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REFERENCES 1. Miller, B.L., “Practical Value of Economic Geology in the Manufacture of Cement” Pit&Quarry, April, 1934. 2. Luster, R., “Raw Materials for Portland Cement: Applications of Conditional Simulation of Coregionalization,” Ph.D. Dissertation, 1985 3. Asad, M.W.A., “Multi-Period Quarry Production Planning through Sequencing Techniques and Sequencing Algorithm,” Journal of Mining Science, 2008, vol. 44, no. 2. 4. Baumgartner, W., “Latest Innovations in Quarry Design and Management,” International Cement Review, 1989. 5. Baumgartner, W. and Honerkamp, M., “Quarry Engineering Design, a Further Step in Computerized Raw Materials Management,” International Cement Review, 1992. 6. Asad, M.W.A., “Development of Optimum Blend/Minimum Cost Scheduling Algorithm for Cement Quarry Operations,” Ph.D. Dissertation, Colorado School of Mines, 2001. 7. Lerchs, H. and Grossman, I.F., “Optimum Design of Open Pit Mines,” CIM Bulletin, 1965, vol. 58, no. 633. 8. Pana, M.T., “The Simulation Approach to Open Pit Design,” 5th APCOM, 1965. 9. Eraslan, K., Çelebi, N., and Paşamehmetoğlu, A., “Açık Ocak Sınırlarının Uretim Planının Bir Fonksiyonu Olarak Simülatif Optimizasyonu,” 16th Mining Congress of Turkey, 1999. 10. Meyer, M., “Applying Linear Programming to the Design of Ultimate Pit Limits,” Management Science, 1969, vol. 16, no. 2. 11. Yegülalp, T.M. and Arias, J.A., “A Fast Algorithm to Solve the Ultimate Pit Problem,” 23rd APCOM, SM, Colorado, 1992. 12. Oran, S., “Research Report of Clay Raw Materials of Batisoke Inc.,” Doğaner Mining, 1998. 13. Onur, A.H., Konak, G., and Karakus, D., “Limestone Quarry Quality Optimization for a Cement Factory in Turkey,” J. South. African Inst. Mining&Metallurgy, 2008, vol. 108.
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