MASTER'S THESIS
Investigation of Borehole Stability in Malmberget
Rajib Ghosh
Master of Science (120 credits) Civil Engineering
Luleå University of Technology
Department of Civil, Environmental and Natural resources engineering
i PREFACE
This thesis is a partial fulfillment of the requirement for the degree of Master of Science in Civil Engineering with specialization in Mining and Geotechnical Engineering at the department of Civil, Environmental and Natural Resources Engineering at Luleå University of Technology, Luleå, Sweden.
This thesis has been sponsored by LKAB in Sweden. The whole thesis work has been carried out at Malmberget. It involves the investigation of borehole instability in different ore bodies in the mine and how instabilities are affected by various mining activities as the mining progresses downward are well described. It was also an opportunity for me to understand the practical problems associated in Rock Mechanics and Rock Engineering field.
I would like to express my sincere gratitude to my supervisor Zongxian Zhang at LKAB, Malmberget, for his unremitting source of assistance during this work. This thesis would not have been accomplished successfully in time without him. I wish to give thanks to my supervisor Ulf Nyberg at Luleå University of Technology for his valuable supervisions and comments. Finally, I am grateful to my examiner Daniel Johansson at Luleå University of Technology for his precise comments.
Special thanks to Anders Nordqvist at LKAB, Kiruna, for his valuable instructions about the setup of camera in the mine and providing necessary data.
Special credit goes to the chargers who have been helpful during the field work. Especially, I have to thank Töre Nilsson for his relentless support during filming.
I am also grateful for getting information and other helps from different personnel at different divisions in the mine. Lars Malmgren, Agenta Nordmark, Thomas Savilahti, Jyri Merilläinen, Thomas Wettainein, Fredrik Ersholm Veronicka Wikström , Joel Andersson, Per Lidström, Hans Älgdahl, Sven-Erik Wennebjörk, Hanna Falksund, Anders Johnsson, Torgny Rynbäck, Peter Malmgren, Knut Sjaunja, Jonas Larsson, Anna- Karin Lantto are highly acknowledged. In electric workshop, Jonathan Nilsson, Josethine Nilsson and Connie Marieharsen are acknowledged for their patience to connect the cable which was damaged several times during filming.
I would like to thank Jesper Martinsson for helping me to create 3-D view to idealize the direction of fault by “Python” programming language.
Finally, I am greatly indebted to my family members for their sacrifices and unconditional support pursuing higher education in Sweden. Friends are also acknowledged for their encouragement and moral support.
Rajib Ghosh October, 2012
ii ABSTRACT
Sublevel caving method is generally selected for large ore bodies with steep slope. This method is based on the gravity flow of the ore to get better recovery. Due to the continuous caving as the mining goes deeper, fractures of hanging wall occur consequently and thus it collapses into the cave. The local stress field is also affected by various mining activities and it initiates the movement of geological structures in the rock mass and causes seismic event frequently. Thus, it is required to investigate instability problems in various ore bodies in the mine as mining advances deeper and deeper. Investigation of boreholes by filming is a technical way to inspect the overall stability in an ore body.
This project work mainly consists of three parts such as Pre-investigation based on production measurement by collecting data from GIRON (Internal production database in LKAB), Field work by filming and Analysis of the data collected from the field. Three ore bodies named Alliansen, Fabian and Vi-Ri were selected for this work.
In the pre-investigation, different problems in the borehole are categorized such as re-drilling, wet holes, stones and concrete in the boreholes in different sublevels where the production was completed or about to complete. Re-drilling maps are drawn in different ore bodies as well. The mine co- ordinates of the ring have been used to locate the approximate area of re-drilling. This pre- investigation enabled us to know which areas in the sublevels are more prone to instabilities in different ore bodies. Thus, drifts were selected around this area in the next sublevels or in the same level for filming. These drifts are classified into three criteria; ongoing production, open cut is finished and open cut has not been done.
In Alliansen, level 992 m and 1022 m have been selected for field work. In addition, level 855m and 880 m in Fabian and 1026 m in Vi-Ri are investigated by filming. It was not possible to get sufficient filming from the level 880 m in Fabian and 1022 m in Alliansen due to the lack of time and instrument problems.
The analysis is done based on production records and field work. In the production records, the percentage of re-drilling has increased to 6.67% from the level 932 m to 962 m in Alliansen and 3.72% from the level 830 m to 855 m in Fabian. Further, the fluctuation of percentage of re-drilling is observed in sublevels in Vi-Ri. Moreover, the percentage of stones found in the boreholes has also increased considerably in different sublevels in this ore body. This analysis is performed based on the total number of holes (which are blasted or charged) in each sublevel.
In the field work, a total of 298 boreholes have been analyzed from the collar to the bottom. Typical modes of instability problems such as shearing, cracking, deformation or breakages inside the boreholes are confirmed. In Alliansen, boreholes are sheared off significantly in a certain part in the sublevels. Besides this, in Fabian, boreholes are caved notably in different drifts. In Vi-Ri, boreholes are broken considerably as well. According to the results from filming, borehole instability problems are affected due to the production sequence is analyzed. It is proved that deformation and cracks are most common problems in boreholes around the ring which was blasted last. However, the causes of deformation or cracks are not only the production activities but also the movement of geological structures and fractures of hanging wall due to the continuous cave as the mining progresses downward change local stress field significantly.
In Alliansen, geologic structures have been analyzed by considering a common shearing plane which could cross subsequent sublevels. The mine co-ordinates of the borehole where it has been sheared or re-drilled are used to get the co-relations among the sublevels. A statistical regression towards the width of the ore body was sufficient to predict that the same shearing plane are crossing several subsequent sublevels. It is also proved that the area which is influenced by more seismic events is the same as the one where several boreholes were re-drilled or sheared. At last, several causes behind the instability problems are discussed and possible recommendations have been given to ensure a safer environment.
iii
TABLE OF CONTENTS
PREFACE ... i
ABSTRACT ... ii
1 INTRODUCTION ... 1
1.1 Problem description ... 1
1.2 Purpose and scope ... 1
1.3 Methodology ... 1
1.4 Structure of the thesis ... 3
1.5 Malmberget Mine ... 4
1.5.1 LKAB’s operation... 4
1.5.2 Description of the mine ... 5
1.5.3 Geology ... 7
1.5.4 Rock Mechanics ... 8
1.5.5 Mining method ... 10
2 LITERATURE REVIEW ... 11
2.1 Modes of failure ... 11
2.1.1 Sheared boreholes ... 11
2.1.2 Deformed boreholes ... 11
2.1.3 Cracked or fractured rock ... 12
2.1.4 Stone –Jammed boreholes ... 12
2.1.5 Empty rooms around boreholes ... 13
2.1.6 Caving of borehole... 13
2.1.7 Drilling Induced failure ... 14
2.1.7.1 Mud weight ... 14
2.1.7.2 Spalling at the corner ... 14
2.2 Possible causes of borehole stability ... 15
2.2.1 Local stress field ... 15
2.2.2 Discontinuity ... 16
2.2.3 Rock blasting ... 17
2.2.4 Caving effect ... 18
3 BOREHOLE FILMING... 20
3.1 Camera Robicam 37 (RC 37) ... 20
3.2 Equipment for field wok ... 22
3.2.1 Steel casing ... 22
3.2.2 Charge truck ... 22
4 PRE-INVESTIGATIONS BY PRODUCTION MEASUREMENT ... 24
4.1 Significance of pre-investigation
... 24
4.2 Problem definition during pre-investigation
... 24
4.3 Pre-investigation of Alliansen
... 25
iv
4.3.1 Map for different types of instability in Alliansen
... 26
4.3.1.1 AL-932
... 26
4.3.1.2 AL-962
... 27
4.3.1.3 AL-992
... 28
4.3.2 Comparison among the sublevels
... 29
4.3.3 Re-drilling map
... 31
4.4 Pre-investigation in Fabian
... 32
4.4.1 FA-830
... 33
4.4.2
FA-855 ... 33
4.4.3 Comparison among the sublevels
... 34
4.4.4 Re-drilling map
... 36
4.5 Pre-investigation of Vi-Ri
... 36
4.5.1 VR-954
... 38
4.5.2 VR-978
... 38
4.5.3 VR-1002
... 40
4.5.4 Re -drilling map
... 42
4.6 Summary
... 43
5 FIELD WORK BY FILMING ... 44
5.1 Different modes of failure
... 44
5.2 Alliansen (AL)
... 45
5.2.1 AL-992-4721
... 47
5.2.2 AL-992-4810
... 50
5.2.3 AL-992-4901
... 51
5.2.4 AL-992-4871
... 54
5.2.5 AL-992-4841
... 56
5.2.6 AL-1022-4790
... 57
5.2.7 AL-1022-4791
... 57
5.2.8 AL-1022-4820
... 58
5.2.9
AL-1022-4850/4851 ... 59
5.3 Fabian (
FA) ... 60
5.3.1 FA-855-1410
... 62
5.3.2 FA-855-2490
... 64
5.3.3 FA-855-2511
... 64
5.3.4 FA-855-8552
... 65
5.3.5 FA-880-1221
... 65
5.3.6 FA-880-1241
... 66
5.3.7 FA-880-1280/1281
... 66
5.4 Vi-Ri (VR)
... 67
5.4.1 VR-1026-7850
... 67
5.4.2 VR-1026-7930
... 69
5.4.3 VR-1026-7910
... 69
5.5 Summary
... 70
v
6 ANALYSES AND RESULTS
... 71
6.1 Alliansen ... 71
6.1.1 Production sequence versus Borehole instability in Alliansen ... 72
6.2 Fabian ... 75
6.2.1 Production sequence versus Borehole instability in Fabian ... 75
6.3 Vi-Ri ... 78
6.3.1 Production sequence versus Borehole instability in Vi-Ri ... 81
6.4 Geological structures in Alliansen ... 82
6.4.1 Geological structure from 962 m to 992 m by Production measurement and previous photographing ... 82
6.4.2 Fault direction by using “Python” programming language ... 85
6.4.3 Seismic event vs. Borehole instability ... 86
7 DISCUSSIONS, CONCLUSIONS AND RECOMMENDATIONS ... 87
7.1 Discussions ... 87
7.2 Conclusions ... 88
7.3 Recommendations ... 90
7.3.1 Recommendations considering equipment used in the field work ... 90
7.3.2 Recommendations regarding mining activity ... 90
7.3.3 Future work ... 90
REFERENCES ... 91
APPENDICES ... 92
Appendix A Borehole instability by production records (GIRON) in different ore bodies ... 92
Appendix B Detailed schedule for field work ... 131
Appendix C Drift, ring and corresponding borehole number filmed during field work ... 134
Appendix D Raw data collected from watching videos for analysis in different ore bodies ... 137
Appendix E The number of observations of different instabilities and their percentages different levels in Alliansen ... 166
Appendix F The number of observations of different instabilities in drift no.4841 in Alliansen-992 m level ... 167
Appendix G The number of observations of different instabilities in drifts no.4790 and 4791 in Alliansen-1022 m Level ... 168
Appendix H The number of observations of different instabilities and their percentages in different levels in Fabian ... 169
Appendix I The number of observations of different instabilities in the drifts no.1280 and 1281 in Fabian-880 m ... 170
vi
Appendix J The number of observations of different instabilities in the drift no.2511
in Fabian-855 m ... 171 Appendix K The number of observations of different instabilities and their percentage in level 1026 m in Vi-Ri ... 171 Appendix L The number of observations of different instabilities in the drift no.7850 in Vi-Ri- 1026 m ... 172 Appendix M The borehole co-ordinates at a depth from where re-drilled has been started in
drifts no.4970 and 5000 in Alliansen -962 m ... 173 Appendix N Borehole co-ordinates at a depth from where re-drilled has been started in drifts no.
4990 and 5020 in Alliansen-992 m ... 178 Appendix O The number of boreholes in different levels in Alliansen (AL) ... 183 Appendix P The number of boreholes in different levels in Fabian (FA) ... 201
Appendix Q The number of boreholes in different levels in Vi-Ri (VR) ... 223
1 1 INTRODUCTION
1.1 Problem description
There are several stability problems that could occur in boreholes such as deformation, shearing, fracturing or caving. In sublevel caving (SLC), all holes in a fan-shaped pattern called ring are being used to get production. If a borehole in a ring has problem of instability, ring cannot be completely charged according to the original charge plan. As a result, poor fragmentation, low recovery of ore, delay in production and higher cost in crushing and grinding may be caused. Hence, a better investigation of the borehole stability is necessary. The investigation can be made by filming inside the borehole in different parts of the ore bodies in the mine.
1.2 Purpose and scope
The main objective of this project work is to investigate various instability problems in boreholes in different ore bodies. For this purpose, three ore bodies such as Alliansen, Fabian, and Vi-Ri have been considered.
By this investigation, it is possible to specify the areas which are prone to instability than the other parts in the same sublevel and thus presume the stability issues in the next sublevels in a certain ore body. It can also be addressed how borehole instability is affected by mining sequence, mine layout and change of local stress field as the mining progresses downward.
In this thesis work, it is possible to analyze a geological structure such as fault or large joint which could cross the several sublevels in the ore body.
Finally, a better treatment can be taken in time regarding production, sustainable mining operation and more safety.
1.3 Methodology
This thesis work was divided into three stages such as data collection from production records (GIRON; internal production database in LKAB), borehole filming with digital camera (Robicam 37) and analysis.
Production records
Prior to go to field work, it was necessary to know what type of instabilities in production holes are recorded in ore bodies in the mine. Several sublevels in three ore bodies are considered to get this information. For this purpose, ring co-ordinates (mine co-ordinates) are used to identify the areas of different instabilities in the ore bodies. Re-drilling map is also made in different sublevels in the ore body. In addition, other instability problems such as stones in the boreholes, concrete in holes and wet holes are also figured out in the map.
In Alliansen, level 932 m, 962 m, and 992 m are considered for pre-investigation. Besides, In Fabian, 830 m and 855 m are studied and the level 954 m, 978 m and 1002 m in Vi-Ri are investigated before we start field work.
Additionally, literatures on borehole stability are reviewed continuously throughout this thesis work.
It included different modes of failure and possible reasons of borehole instability in the mine.
2 Borehole filming
Boreholes are filmed in selected ore bodies in the mine. A digital camera (Robicam 37) has been used to inspect different modes of failures inside the boreholes in different sublevels in ore bodies. A charge truck pipe was used to hold the steel case with camera in the borehole.
After analysis of production records in upper sublevels, drifts were selected in the next sublevels according to the area which are predicted to be prone in borehole instability problems by considering the analysis in production records. Moreover, three criteria were considered on production sequence to choose those drifts for filming.
In this field work, typical problems in the borehole are confirmed in different ore bodies. During field work, borehole was carefully observed in each meter of the borehole.
In Alliansen, level 992 m and 1022 m were selected for filming. The level 855 m and 880 m in Fabian and the level 1026 m in Vi-Ri were used to perform this field work.
Analysis
After collection of data from extensive filming, boreholes are analyzed for each meter. Likewise, about three hundred boreholes are examined in this thesis work. Analysis is done based on number of the observations of different instability problems in boreholes.
In the analysis, instability problems are compared for different sublevels in each ore body. Further, different cases are interpreted based on production sequence. For example, how borehole instability is affected around the ring which is blasted last is well described.
Geological structures are analyzed in Alliansen based on production records and field work by filming. Borehole co-ordinates where it was re-drilled are used to analyze the fault which was previously confirmed in photographing from 962 m to 992 m level. It has also been verified that this re-drilling in a particular area in Alliansen has often been done for sheared boreholes. After field work in that particular area, sheared boreholes are also confirmed. Thus, the possible gradient of fault is determined. The existence of fault plane is analyzed along the width of the ore body.
Python programming language is used to visualize the continuation of fault gradient from sublevel to sublevel in specific area in Alliansen. The mine co-ordinates (X, Y, Z) of the boreholes at sheared depth or re-drilled depth were considered.
Finally, seismic data are studied in that area during the period 2010-01-01 to 2012-08-24 from the level 962 m to 1022 m. Seismic responses from the ore pass were not considered in this study.
3 1.4 Structure of the thesis
Figure 1.1 Different stages followed in this thesis work.
(* means selected sublevels for field study)
Investigation of borehole stability at Malmberget, LKAB
Different modes of borehole instability
Investigation techniques
Pre-investigation by collecting data from online production database (GIRON: V02.029)
Field study by Borehole filming for different sublevels in different ore bodies.
Map of different stability problems Alliansen(932,962,992*, 1022*), Fabian (830, 855*, 880*) and Vi-Ri (954, 978, 1002, 1026*)
Analysis of field study Theoretical analysis of geological
structure (fault) in Alliansen
Discussion, Recommendation and Future Study Literature review
Objective
4 1.5 Malmberget Mine
1.5.1 LKAB’s operation
Loussavaara Kirunavaara AB (LKAB) is a high-tech international mining company and one of the environmental-friendly leading producers of upgraded iron ore products. It has been founded in 1890 and has been 100% state-owned since 1950. Since early 1900, the company has started industrial extraction from the mines in Kiruna and Malmberget after completion of railway from Luleå to Malmberget, Kiruna and harbors at Norway and it has been further extended to the Svappavaara.
Figure 1.2 shows the locations of LKAB’s operations in northern Sweden and Norway and form a continuous flow from the mining and processing of ore to the transportation of the finished products (by railway) from the mines to the harbors.
Figure 1.2 LKAB operational areas (LKAB database).
According to recent statistics (Annual report of LKAB, 2011), annual production of planned crude ore at Kiruna and Malmberget are 24 Mt and 16 Mt (Million tonnes) respectively and final products are 26.1 Mt of which pellets are 22.1 Mt. Table 1.1 shows the comparison between mineral reserve and mineral resources at LKAB until 2011.
5
Table 1.1 Mineral reserve and mineral resources at LKAB (Annual report, 2011).
*Note: Quantity is measured in Mt (=Million tonnes).
1.5.2 Description of the mine
There are approximately 20 large and small ore bodies distributed over Malmberget in which 9 are currently being mined (Figure 1.3). The length and width of the ore bodies are around 5 km and 2.5 km respectively. It consists of two major ore fields called Eastern and Western. At first, open pit mining was done and underground operation has been started since 1950. Sublevel caving has been the principal mining method since 1960.
Figure 1.3 Malmberget Mine (www.lkabframtid.com).
Indicator
Amount of ore ,Mt
until 31 December ,2011 Considered level
Kiruna Malmberget
Kiruna Malmberget Quantity % Fe Quantity % Fe
Mineral reserve
Proven 590 48.7 174 42.4
Above 1365 m
For Western field, above 600 m and for eastern field, above 1250 m
Probable 76 47.1 105 41.2
Mineral resources
Measured 93 48.9 21 39.8
Above 1500 m
For western field, from 600 to 800 m and for eastern field ,from 1250 to 1450 m
Indicated 160 45.7 175 39.8
6
Eastern part of the field consists of Alliansen, Fabian, Dennewitz, Parta, Printzsköld, Östergruvan, Vi- Ri and Western part of the field consists of Välkomman, Baron, Johannes, Hens, Josefina. Blue area represents magnetite and pink area represents hematite ore bodies (Figure 1.4).
N
Figure 1.4 Horizontal layout of Malmberget Mine (LKAB database).
Now, there is one main haulage level at 600 m in the western part of the mine and two main haulage levels are at 1000 m and 1250 m in the eastern part of the mine.
There are two ore passes connected with 600 m level and seven ore passes connected with 1000 m level and five with the 1250 m level. In the western part of the mine, two ore passes are being used to transport the material from production level at Välkomman 450 m and Johannes 547 m to the main haulage level at 600 m. Trucks are being used for other ore bodies like Baron 615 m ,Hens 635 m and Josefina 580 m in western field. In the eastern part of the mine, there are three ore passes in Fabian, Printzsköld and one ore pass in Dennewitz connected with main haulage level at 1000 m respectively. Trucks are being used for Östergruvan 957 m and Alliansen 992 m for transporting the material to the crusher. In same part of the mine, there are two ore passes from Alliansen 1022 m and Vi- Ri 1002 m each and one from Parta connected with new main haulage level at 1250 m.
There are five crushers; one at 600 m level, two at 1000 m and two at 1250 m level respectively. At the same level, distance between the crushers is around 100 m.
7
There are five vertical shafts available for transporting ore to the surface after crushing. Two vertical shafts are at 815 m and 1250 m level each and one at 600 m level up to the surface. The ore is hoisted up from 1250 m to the 1000 m level by shaft and then carried by the conveyor belt up to the 815 m level and skip up to the surface through two shafts at 815 m level .The other vertical shaft is being used from 600 m level up to the surface. At the same level, distance between two vertical shafts is around 22 m.
1.5.3 Geology
The Malmberget deposit is one of the world’s largest apatite -iron (low titanium content between 0.04% and 0.31%) ores. In the western part of the mine, the ores form a more -or- less continuous, undulating band of lens shaped ore bodies. The ores in the eastern part of the mine are intensively folded and tectonically deformed. The average dip of the ore bodies varies from 45o to 70o. The average width of the ore bodies ranges from 20 to 100 m. About 90% of the ore is magnetite and the rest is hematite. Mostly, hematite is found in western part. The iron content varies from 54 to 63%
(Hedstrom et al., 2001).
The country rocks at Malmberget consists of metamorphosed volcanic rocks such as gneisses and fine-grained feldspar-quartz rocks called leptites. Granite veins often intrude the ore (Hedstrom et al., 2001).
Figure 1.5 shows simplified geological map of the Northern ore province with the economic deposits market in red and Figure 1.6 shows geology of the Malmberget area.
Figure1.5 Geology of northern Norrbotten with excursion stops (Martinsson and Wanhainen, 2000).
8
Figure 1.6 Geology of the Malmberget area (modified from Geijer, 1930).
1.5.4 Rock mechanics
The primary or undisturbed state of stress in Malmberget mining area was analyzed by Sandström and Nordlund (2004). They have recommended the following stress magnitude and orientation.
ϬH = 0.037 z MPa, maximum horizontal principle stress (East-West).
Ϭh= 0.028 z MPa, minimum horizontal principle stress(North-South).
Ϭv= 0.029 z MPa, vertical principle stress.
Table 1.2 shows stress magnitude (ϬH, Ϭh) and orientation (Trend) at Malmberget in 2007 measured from hydraulic fracturing.
Table 1.2 Stress measurement from hydraulic fracturing (Ask et al., 2009; Sjöberg 2008) Measurement
Cluster no
Mine level m
ϬH [MPa]
Ϭh [MPa]
Trend of ϬH [MPa]
Trend of Ϭh [MPa]
1 1170 49.6 23.9 128o 38o
2 1300 40.8 22.1 137o 47o
Mean 1 and 2 - 45.2 23.1 132o 42o
9 Ϭv= ρgz Pa, vertical principle stress.
Where, ρ =density of rock mass, kg/m3. Density of ore and side rock is about 4500 kg/m3 and 2800 kg/m3, respectively (Zhang, 2012).
z = depth below the top of the mountain in meter.
g = gravitational constant=9.81 m/sec2.
Figure 1.7 shows stress orientation at Malmberget ore deposit in three dimensions.
Figure 1.7 Virgin or primary stress orientations at Malmberget mine (Wettainen, 2012).
10
At the Malmberget mine, uniaxial compressive strength of ore ranges between 85 and 140 MPa and same for red leptite varies between 170 to 220 MPa and for gray leptite varies between 70 and 160 MPa. The gray leptite often carries a very high amount of biotite and kaolin concentrated in thin separated layers otherwise rather strong rock. Over the entire ore field one structural group strikes and dip sub-parallel to the ore bodies. The RQD for the ore varies between 35% and 60% and for the side rocks between 55 and 75 % (Hedstrom et al., 2001).
1.5.5 Mining method
Generally, Sublevel caving has been used as a major mining method since 1960s at Malmberget.
Initially, small –scale sublevel caving (sublevel height-15 m) was used and later, large scale sublevel caving has been used (sublevel height-20 to 30 m) for reduction of cost of development which was the key factor for survival of the company in international competitive market.
In Malmberget, transverse sublevel caving has been used almost in all of the ore bodies except Baron.
Longitudinal sublevel caving is being used in Baron. The major factors of choosing different sublevel caving methods were the shape of the ore body, dip and strike of the ore body, in situ stresses and frequency and orientations of the discontinuities in the rock mass. For narrow ore body, longitudinal sublevel caving and for wide ore body, transverse sublevel caving has been considered.
Tucker (1981) reports that at Pea Ridge, the incidence of stress-induced instability was significantly reduced when longitudinal sublevel caving was replaced with a transverse method.
Figure 1.8 shows transverse sublevel caving and Figure 1.9 shows cross-section of drift layout which is being practiced mostly at Malmberget.
Figure 1.9 Typical cross-section of drift layout at Malmberget.
22.5 m 20 to 30 m
20 to 30 m
7 m
5.5m
Figure 1.8 Transverse sublevel caving (Courtesy by Atlas Copco).
11 2 LITERATURE REVIEW
2.1 Modes of failure 2.1.1 Sheared borehole
Borehole could be sheared by discontinuities such as movement of fault or joint. Figure 2.1 shows schematic presentation of borehole shearing when crossing a discontinuity (Peng and Zhang, 2007).
Figure 2.1 Borehole shearing.
2.1.2 Deformed boreholes
Borehole could be deformed due to the variation of local stress field. Borehole breakout occurs due to the induced compressive stress and it occurs parallel to the minor principal stress (see Figure 2.2).
Local stress might be induced by various mining activities such as excavation, mining sequence, mining layout or even mining method.
Figure 2.2 Breakout of borehole (Chowdhury, H.A., 2006).
12 2.1.3 Tensile cracked or fractured
Borehole could be fractured due to the variation of local stress field or a weak zone. Tensile crack occurs due to the pull out of the material parallel to the major principal stress (SH), see Figure 2.3.
Figure 2.3 Tensile Crack along the major principal stress (Peng and Zhang 2007).
2.1.4 Stone –Jammed boreholes
Mostly borehole can be jammed by stone due to the deformation of borehole or by shearing .
For example, when deformation in a borehole continues, the borehole may be collapsed or be fractured and finally it may become a stone-jammed borehole (
Zhang 2012). Figure 2.4 illustrates stone- jammed borehole in the drift 805 in Fabian (
Kangas 2007a) atMalmberget mine.
Figure 2.4 Stone jammed borehole in the drift of Fabian 805(Kangas 2007a).
13 2.1.5 Empty rooms around boreholes
If an empty room or a cavity exists inside the ore body, a charge pipe can get stuck at a place and pump too much explosive into the cavity (Figure 2.5) and thus making less efficient blasting (according to the observations of the chargers at Malmberget mine).
Figure 2.5 Loss of explosive due to the empty rooms around boreholes.
But such empty rooms or cavities have not been found by filming in previous investigation (Zhang 2012).However, according to the chargers, they have found loss of explosive in a single hole. Hence, more investigations are needed to find this kind of cavities.
2.1.6 Caving of borehole
Caving of borehole may happen due to the deformation of the borehole (see Figure 2.6).
Figure 2.6 Hole 6 of ring 30 are caved in the drift of AL- 479 (kangas, 2007a).
From the previous investigation of Kangas 2007a, borehole 6 of the ring 30 was caved in drift no.479 at 902 m level in Alliansen (AL).It was reported that the major problem of the ore body “Alliansen”
are caving and shearing in the borehole.
14 2.1.7 Drilling induced failure
2.1.7.1 Mud weight
As a borehole is drilled, hydraulic pressure of the drilling mud must replace the support lost by removal of rock. But mud pressure (or mud weight) being uniform in all direction cannot exactly balance the earth stress. Consequently, rock surrounding the borehole is distorted or stained and may fail if the redistributed stress exceed the rock strength (Addis et al., 1993). There are two possible failure such as tensile and compression failure. Tensile failure (Figure 2.7 a) occurs when mud weight overcomes borehole stresses and rock tensile strength producing a fracture. On the other hand, compressional failure (Figure 2.7 b) can occur at high or low mud weight. Stability problems are minimized when the two principal stresses normal to the borehole trajectory are nearly equal.
Figure 2.7 Failure due to the mud weight a) tensile failure, and b) compression failure (Addis et al., 1993.)
2.1.7.2 Borehole spalling at the corner
Stress concentration at the bottom (means collar in this thesis work) of a borehole due to the corners with small radius of curvature in an axial section is considered. The spalling can occur continuously with drilling and results in continuous spalling with depth, i.e., a breakout. This type of breakout tends to form on one side of the borehole and its orientation is approximately perpendicular to the orientation of standard breakouts, inferred from the stress concentration due to the cylindrical shape of the borehole (Hayashi, Ito and Kurosawa 1998).
Figure 2.8 (a) and (b) illustrates radius of curvature at the corner due to the inaccuracy of drilling and change in the borehole shape with progress of drilling due to the spalling represented as the dark area(Hayashi, Ito and Kurosawa 1998).It also shows that spalling occurs at ψ=0 at collar. Spalling increases with the progress of drilling at ψ=90o and 270o in which ψ is an angle in a polar co-ordinate system in a cylindrical hole and S2 is a remote principal compressive stress (virgin stress).
15
Figure 2.8 Deformed section of a borehole a) radius of curvature at corner in longitudinal section and, b) change of shape with the progress of drilling due to the spalling.(Note: x1 and x2 are the axes in rectangular co- ordinate system)
2.2 POSSIBLE CAUSES FOR THE BOREHOLE STABILITY 2.2.1 Local stress field
Around the borehole, a stress arch is generated to redistribute earth stresses. At the opening, tangential stresses are higher than the radial stresses. To get more stable borehole, the orientation of borehole should be such a way that principal stress normal to the longitudinal axis of the borehole could be minimized (Dusseault, 2005).
Figure2.9 represents borehole stresses and Figure 2.10 shows that tangential stress (Ϭ’θ) are greater at boundary and decreases from the opening to the far end and reaches maximum in-situ stress and radial stresses(Ϭ’r) are increasing until certain level and reaches minimum in-situ stress.
Figure2.9 In situ stress around borehole Figure 2.10 Tangential and radial stress variation with the radius (Dusseault, 2005). (Dusseault, 2005).
16
Figure 2.11 shows principal stress trajectories after drilling a borehole. Concerning borehole stability, local stress is further affected by mining sequence, mining layout or even mining method. In mining sequence, excavation schedule of drift affects borehole stability and in turn affects blasting efficiency and fragmentation. In mining layout, drift size and orientation affects local stress field and thus also influences borehole stability. In mining method, whenever we have several alternatives to mine out the area, production and economy should not be considered always key factors before the actual mining starts. In this Figure, Yellow area represents the highest stress magnitude around the opening and it decreases further away from the boundary .
Figure 2.11 Principal stress trajectories (Dusseault, 2005).
2.2.2 Discontinuity
Rock masses are far from being continuum and consist essentially of two constituents: intact rock and discontinuities (planes of weakness). Rock discontinuities include joints, fractures, faults and other geological structures. Also, compared to intact rock, jointed rock shows higher permeability, reduced shear strength along the planes of discontinuity and increased deformability and negligible tensile strength in directions normal to those planes.
Stress created due to the borehole often causes movement of joint and further it could create borehole stability problem. Due to the sliding of joint plane, rock near the joint can be broken into large or small pieces and it can fall into the borehole and jam the holes (Abousleiman et al., 2007).
If there is a fault or a large joint inside in the rock mass, a borehole can be sheared into two parts along the sliding plane. Further, it could decrease the cross-sectional area of the borehole and then we are not able to put charge pipe straight through the shearing plane. Thus, we cannot charge the remaining portion of the borehole and definitely, we will get less efficient blasting and thus make less production and poor fragmentation.
Figure 2.12 shows a typical shearing occurred in boreholes in which a fault goes through
at drift no.
499 in level 992 m at Malmberget mine, LKAB, Sweden
(Zhang, 2012).17 Figure 2.12 Sheared borehole (Zhang, 2012).
2.2.3 Rock blasting
In sublevel caving, a production blast is performed to each fan or ring. In the drift, first ring will be blasted when the second ring has already been pre-charged, see Figure 2.13. Because, if we blast the first ring without pre-charging of second ring then it could be difficult to put the charge pipes inside if borehole deforms due to the blasting of first ring and it would make less efficient blasting in second ring.
In fan shaped, center parts of the holes has been initiating earlier than the end holes to minimize the borehole instability immediately in the drift of the next sublevel.
Figure 2.13 Borehole instability due to blasting.
18 2.2.4 Caving effect
Sublevel caving method is based on gravity flow of blasted ore and caving waste. Figure 2.14 shows that the amount of ore is supposed to extract as an ideal ellipsoid (Brady and Brown, 2006). Today, with the continuing push to increase mining scale, a fundamental question is whether the gravity flow principles which served as the design basis for the small-scale sublevel caving mine designs of the past can be applied at much larger scales or whether some other approach is required (Hustrulid, 2009).
Figure 2.15 illustrates a further cause of stress concentration around the production levels in sublevel caving operations. As mining progresses downwards with the removal of ore and the attendant caving of the waste rock, the in situ stresses are redistributed to the supported rock. Some vertical stress will be transmitted to the new mining horizon by the caved waste but by far the greater effect will be the concentration of horizontal stresses in the lower abutment zone. In that circumstances if we drill the borehole immediate vicinity of the concentration of the major principle stress, then there is a chance of deformation inside the borehole (Brady and Brown, 2006).
As mining progresses downward, the flow of gravity of caving waste increases and it causes more variation of local stress field and it could create more stability problem in borehole at great depth.
Induced stress will be less severe around the boundaries of production headings driven parallel to the high horizontal stresses (Brady and Brown, 2006).
Figure 2.14 Gravity flow of blasted ore in sublevel caving mechanism (Brady and Brown, 2006).
19
Figure 2.15 Schematic illustration of the transverse horizontal stress concentration produced in the mining area (Brady and Brown, 2006).
Figure 2.16 shows three stages of time dependent deformation of the hanging wall in Kiirunavaara Mine, LKAB, Sweden. The graph displays two curves showing velocity (dashed line) and displacement (continuous line) in the East-West direction for station T5. This station is located on a waste dump in one of the highest locations of the hanging wall ground surface. The regressive stage is characterized where acceleration is initiated by the exploitation of a new sublevel. The behavior changes to a progressive stage when the displacement reaches the onset of failure. In this second stage the movement accelerates until the point of failure which defines the start of the steady state stage where the rate of movement is constant. Finally, a second progressive stage starts with the proximity of the caving zone where the movement accelerates until collapse (Norlund and Villegas, 2010).
In Malmberget mine, LKAB, Sweden, borehole instability has been found beyond the solid hanging wall. Under a solid hanging wall (skalning in Swedish), there was never stability problem because the effect of flow of caving comes on borehole beyond the solid hanging wall (Zhang, 2012).
Figure 2.16 Time versus accumulated displacement in East-West direction for station (Norlund and Villegas, 2010).
20 3 BOREHOLE FILMING
A Camera Robicam 37 (RC 37) has been used for borehole filming. The objective of using this camera is to inspect the borehole in different ore bodies in the mine. By this filming, an investigation of the borehole instability has been performed. A total of 298 boreholes (Table 3.1) have been filmed in three large ore bodies named Alliansen (AL), Fabian (FA) and Vi-Ri (VR) to make documentation and to analyze for various failure mechanisms inside the boreholes.
Table 3.1 Number of the borehole filmed for different ore bodies.
3.1 Camera Robicam 37 (RC 37)
Followings are the arrangement of Robicam 37 for filming.
1. It consists of Ø37x90 mm camera in which the diameter of the lens is 37 mm and the length of the camera is 90 mm (Figure 3.1).
Figure 3.1 RC 37
2. It has been connected with 7” monitor (Figure 3.2) with measured color display (6.1”x3.22”).
Orebody Level
m
Total numbers of boreholes at each
level
Total numbers of boreholes filmed in each ore body
Total numbers of boreholes filmed
AL 992 90
168
1022 78 298
FA 855 31
880 37 68
VR 1026 62 62
37 mm
21 Figure 3.2 Monitor with camera
3. A 60m long cable is included with camera to reach the maximum height of the borehole. Each meter is assigned by marking numbers (Figure 3.3).
Figure 3.3 Cable connected with the camera a) wrapped and b) marking by numbers.
4. A powerful battery (12V 3000 mAh) provides several hours of operating time.
5. Remote control system has been used to record the video inside the borehole (Figure 3.4).
Figure 3.4 Remote control device.
22
6. SD card (external memory) is used for saving the recording videos.
3.2 Equipment for field wok
3.2.1 Steel casing
Two separate steel casing has been used to hold the camera inside the borehole. In order to ensure safety for the camera, a steel casing (Ø6x13 cm) (Figure 3.5 a) has been used around the camera and camera is clamped by screw from the outside of the steel casing. The second part of the steel casing (Ø6x64 cm) (Figure 3.5 b) is used to fasten the charge pipe with first part of the steel casing (Figure 3.5 a) with camera as shown in Figure 3.5 . Two parts are connected by screwing on. Charge pipe has been clamped by the screws with the second part of the pipe (Figure 3.6).
Figure 3.5 Steel casing used a) for camera to the left and b) to hold the charge pipe to the right.
Figure 3.6 The two parts are screwed together.
3.2.2 Charge truck
A charge truck pipe has been used to fasten the whole steel casing in order to keep the camera inside the borehole (Figure 3.7). Video has been recorded by holding the charge pipe with camera at every one meter along the production hole. The depth has been monitored with help of a digital counter in charge truck.
23 .
Figure 3.7 Camera in the steel casing with charge truck.
Steel casing with camera inside
Charge pipe
24
4 PRE-INVESTIGATION BY PRODUCTION MEASUREMENT 4.1 Significance of pre-investigation
The objective of the pre-investigation is to find different types of borehole instability in upper sublevels of various ore bodies prior to go to the next sublevels for field work. Hence it is easy to select the drifts where the similar problems could be found by filming. The other reason of doing pre- investigation is to find any geological structure which could cross the different sublevels in different ore bodies and how it could be characterized in the plot with suitable consideration by comparing the production measurement and field work. Hence, the better investigation could be done by observing problem statistics from sublevel to sublevel. It could also indicate where the borehole instability problem is governing in different sublevels of different ore bodies. Three ore bodies have been considered for this pre-investigation and field work as well. The data collected from GIRON (internal online production database being updated regularly) is used for pre-investigation. Table 4.1 shows the schedule of pre-investigation for this project work.
Table 4.1 Schedule for pre-investigation.
4.2 Problem definition during pre-investigation
Four types of major borehole stability problems have been identified. These are re-drilling, wet holes, stones and concrete in the holes. Followings are the definitions behind the consideration of those problems.
• Re-drilling: Re-drilling is to be done when the chargers are not able to charge the hole and it needs to drill again due to the shearing of borehole, jammed by stone or caved rock from the top of the borehole from upper sublevels.
• Wet holes: When water is found in the hole, then chargers have to leave the borehole for the time being and later they will charge before blasting.
• Stone: Stone has been found by several reasons. Mostly, caved rock is coming inside from the upper sublevels where production has been completed or due to the deformation or due to the shearing of joints or faults adjacent to the borehole.
• Concrete: Concrete could be found from shotcreting at the roof or from the floor of the upper blasted sublevels.
Ore body Levels, m
Alliansen (AL) 932, 962, 992
Fabian (FA) 830, 855
Vi-Ri (VR) 954, 978, 1002
25 4.3 Pre-investigation of Alliansen
For Alliansen, three sublevels 932 m , 962 m and 992 m have been considered for pre-investigation.
The sublevels 932 m and 962 m have been mined out for production (Figure 4.1 and 4.2) and level 992 m has not been completed yet (Figure 4.3) as the analysis is done. In those Figures, white, yellow, red and blue colors show the loading has been completed, only drilling has been done, charging and blasting has been done respectively.
.
Figure 4.1 Drift layout at Level 932 m .
Figure 4.2 Drift layout at Level 962 m.
Production has been completed
Production has been completed except some rings with the color of deep orange for biotite layers.
26 Figure 4.3 Drift layout at Level 992 m.
4.3.1 Map for different types of instability in Alliansen
Maps of various instabilities have been drawn using co-ordinate of rings mentioned in GIRON in different sublevels in Alliansen. Two dimensional co-ordinate systems have been introduced to draw this map. The co-ordinates of the rings which have different instable boreholes have been considered to identify the region of instability problems in different parts of the sublevel. In this map, X and Y represent mine co-ordinates (in meter) of the ring.
4.3.1.1 AL-932
From this level, mostly re-drilling and wet holes have been found from X=+50 m to -100 m and Y=+1900m to +2100 m where the drifts no. 4780, 4781, 4810, 4840,4871,4900,4901, 4930, 4960 were situated (Figure 4.4). Solid line represents the boundary of the ore and dashed line corresponds to most problematic area in that level.
Production has not been done from those rings.
Production has been done from those rings.
27 Figure 4.4 Map for AL-932m (Data in Appendix A.1).
4.3.1.2 AL-962
Mostly, re-drilling has been done from X=+25 m to -200 m and Y=+1930 m to +2200 m (Figure 4.5) where the drifts no.4820, 4840,4850,4880,488,4910,4911,4940,4970 and 5000 were situated.
From these two levels, instability has been increased towards hanging wall side to a certain extent from AL-932 m to AL-962 m.
-200 -150 -100 -50 0 50 100
1600 1700 1800 1900 2000 2100 2200 2300
wet holes
stone in hole redrilling
concrete
Y (m)
X (m)
AL-932
foot wall
hanging wall
most problemtic zone approximate boundary of orebody
28 Figure 4.5 Map for AL-962m (Data in Appendix A.2)
4.3.1.3 AL-992
In this level, re-drilling and wet holes are assigned as a major problem from X= -50 m to -200 m and Y=+2000 m to +2150 m (Figure 4.6) in which the drifts no. 4930, 4960,4990,5020,5050 and 5080 were situated.
-250 -200 -150 -100 -50 0 50 100
1700 1800 1900 2000 2100 2200
wet holes stone in hole redrilling concrete
AL-962 Y(m)
X(m)
Most problematic zone
Approximate boundary of orebody
foot wall
hanging wall
29 Figure 4.6 Map for AL-992m (Data in Appendix A.3)
4.3.2 Comparison among the sublevels
From the map of different instability among different sublevels, major problematic region has been identified and the common area among the different sublevels with most instability problem has been located by red color and it ranges from X= -50 m to -100 m and Y = +2000 m to +2100 m (Figure 4.7). It has been considered as a most vulnerable zone for Alliansen by considering production measurement (GIRON).
It can also be suggested that instability of borehole moves from upper to lower sublevel towards the hanging wall side. For better investigation, some drifts have been chosen around this problematic area at the next sublevel for filming.
-250 -200 -150 -100 -50 0
1690 1790 1890 1990 2090 2190 2290
wet hole stone in the hole redrilling concrete in the hole
Y(m)
X(m)
AL-992
Most problematic zone
Approximate boundary of orebody
foot wall
hanging wall
30
Figure 4.7 Common area of borehole instability from 932 m to 992 m (Data in Appendix A.4).
By considering production records in GIRON (production website in LKAB), borehole instability varies from sublevel to sublevel. Figure 4.8 shows that re-drilling has increased to 6.67% at level 962 m. It has fluctuated to 5.44% at level 992 m. This analysis has been performed until 2012-05-10 in which levels 932 m and 962 m are completed in production. On 992 m level, we have considered 64.32% boreholes* to get this statistics. The remaining 35.68% boreholes had not been charged when the analysis was done.
Figure 4.8 Comparison among the sublevels regarding borehole instability (Data in Appendix A.5and O).
Foot wall Hanging wall Y(m)
X (m)
0 1 2 3 4 5 6 7
932 962 992
3,21
2,81
1,71 1,07
1,74
1,08 4,62
6,67
5,44
0,2317 0,21 0,0592
wet holes,%
stone,%
redrill, % concrete, %
Borehole instability in percent
Sublevel height, m
* Total boreholes which were blasted or charged since instabilities of boreholes are being recorded in production data just before charging.
31 4.3.3 Re-drilling map
Since the re-drilling is as a major problem in Alliansen, re-drilling map among the different sublevels have been drawn (Figure 4.9). From the previous photographing (Zhang, 2012), it has been proved that there is a geological structure fault shearing several boreholes in the drifts no. 4930, 4960, 4990 at 992 m level which is marked in the following Figure. From the present analysis, we got the continuation of re-drilling from 962 m to 992 m level and thus, we are predicting that this re-drilling was done from the continuation of shearing by the same fault from level 962 m to 992 m since shearing plane is following a parallel direction with the ore body through the sublevels. Later, geological structure for this located zone has been analyzed.
Figure 4.9 Re-drilling map from 932m to 992m(Data in Appendix A.6).
In this marked area, the horizontal co-ordinate of rings which have got sheared boreholes have been located from the drifts no. 4940, 4970, 5000, 5030, 5060, 5090 at 962 level to the 4930, 4960, 4990, 5020,5050, 5080 at level 992 m (predicted by production measurement and later proved by theoretical analysis in chapter 6). It can also be suggested that more re-drilling was done in this area which ranges from X= -20 m to X= -120 m and from Y= +2025 m to Y= +2150 m that also satisfies the zone approximately analyzed in Figure 4.7.
-160 -140 -120 -100 -80 -60 -40 -20 0 20 40
1600 1700 1800 1900 2000 2100 2200
AL-932 AL-962 AL-992
X (m)
Y(m
)
Foot wall
Hanging wall
32 4.4 Pre-investigation in Fabian
Fabian is one of the largest ore body in Malmberget mine and its width increases as the mining progresses downward. The dip is about 90o. For pre-investigation, two sublevels 830 m and 855 m have been selected prior to start field work. Production has been completed for 830 m but level 855 m has not been mined out fully as the analysis is done. These two levels have been showed in the following Figures 4.10 and 4.11.
.
Figure 4.10 Drift layout for FA-830 m.
Figure 4.11 Drift layout for FA-855m.
Production has been completed
Production has been completed
Production has not been completed
33 4.4.1 FA-830
On this level, instability of borehole has been found mostly from X= -1400 m to X= -1700 m and Y=+700 m to Y=+950 m where X and Y correspond to the horizontal plane in the mine (Figure 4.12). It includes almost 80% drifts such as 8301,2620,2600, 2580, 2560, 2540, 2520, 2500, 2480, 2460, 1460, 1440, 1420, 1400, 1380, 1360 and 1340 in that level. Wet holes have been observed mostly even though there are some stones and few re-drilling have also been found.
Figure 4.12 Map of instability at FA-830 m. (Data in Appendix A.7).
4.4.2 FA-855
At this level, the number of re-drilling has been increased and there are also some wet holes and concrete found in the major problematic area which ranges from X= -1450 m to X= -1700 m and from Y=+750 m to +950 m (Figure 4.13).The drifts were 2570, 2550, 2551, 2530, 2531, 2510, 2511, 2490, 2491, 2470, 2450,1450,1430,1410,1390,1370,1350 and 1330 in that region.
-1800 -1700 -1600 -1500 -1400 -1300 -1200
700 800 900 1000 1100
wet holes
stone
redrilling
concrete Y(m)
X(m)
FA-830
Foot wall
Hanging wall Most problematic zone
Approximate boundary of orebody
34
Figure 4.13 Map of instability at FA-855m. (Data in Appendix A.8).
4.4.3 Comparison among the sublevels
After analysis between FA-830 m and FA-855 m, the common area in which most instability of borehole has been found ranges from X= -1450 m to X= -1700 m and Y = +750 m to Y= +950 m . Instability has moved from level 830 m to 855 m towards the hanging wall side (Figure 4.14).
From the previous report (Kangas, 2007a), caving was reported as a major problem in Fabian. Shear zone has not been identified by filming. From pre-investigation in this thesis work, we could predict that this re-drilling was done for caved rock regardless shear zone prior we go to filming.
By comparing data from level 830 m to 855 m, re-drilling has increased to 3.72% at level 855 m. The percent of wet holes has decreased from 3.87 % to 3.74 % (Figure 4.15).This analysis has been performed until 2012-05-10 in which levels 830 m are completed in production. On 855m level, we have considered 61.08% boreholes* to get this statistics. The remaining 38.92% boreholes had not been charged when the analysis was done.
-1700 -1600 -1500 -1400 -1300 -1200
750 850 950 1050
wet holes
stones
redrilling
concrete Y(m)
X(m) FA-855
Foot wall
Hanging wall Most problematic zone
Approximate boundary of orebody
* Total boreholes which were blasted or charged since instabilities of boreholes are being recorded in production data just before charging.
35
Figure 4.14 Common area of borehole instability from 830 m to 855 m (Data in Appendix A.9).
Figure 4.15 Comparison among the sublevels regarding borehole instability (Data in Appendix A.10 and P).
Y(m)
X(m)
0 0,5 1 1,5 2 2,5 3 3,5 4
830 855
3,87 3,74
1,89
2,24
1
3,72
0,22
0,83
Borehole instability in percent
Sublevel height, m
wet holes ,%
stone,%
redrill,%
concrete,%
36 4.4.4 Re-drilling map
A re-drilling map has been drawn from level 830 m to 880 m in Fabian where 830 m was mined out fully but the production was done more than 70% from 855 m and the level 880 m has just been started as the analysis is done in this project work.
From this re-drilling map, we can conclude that instability of borehole does not follow any regular direction from upper sublevel to lower which we found from Alliansen (Figure 4.16). The major type of instability might be different in Alliansen from Fabian.
Figure 4.16 Re-drilling map among different sublevels (Data in Appendix A.11).
4.5 Pre-investigation of Vi-Ri
Vi-Ri is one of the deepest ore body in Malmberget mine, LKAB. Its dip is about 45o.Three levels 954 m ,978 m and 1002 m have been considered for pre-investigation prior to start field work where 954 m and 978 m were already mined out (Figure 4.17 and 4.18) and production was about to complete in level 1002 m (Figure 4.19).
-1700 -1600 -1500 -1400 -1300 -1200
600 650 700 750 800 850 900 950 1000 1050 1100
FA-830 FA-855 FA-880 Y(m)
X(m)
Foot wall
Hanging wall
37 Figure 4.17 Drift layout for VR-954 m.
Figure 4.18 Drift layout for VR-978 m.
Production has been completed
38 Figure 4.19 Drift layout for VR-1002m.
4.5.1 VR-954
At level 954 m , wet holes have been found mostly from X= -840 m to X= -1000 m and from Y=
+2600 m to Y= +2825 m with some stones in the hole (red dashed line).This area represents more water than the other part for that level and it includes the drifts no.7780, 7800, 7820, 7840, 7860, 7880, 7900, 7920, 7940,7960 and 7980. The area of blue dashed line shows some re-drilling and stone in the hole. Solid line shows the boundary of the ore body (Figure 4.20).
4.5.2 VR-9 78
At level 978 m, the maximum number of wet holes have been found from X= -900 m to X= -1020 m and from Y= +2550 m to Y= +2800 m and it also includes the previous sublevel 954 m . The drifts were 7750, 7770, 7790, 7810, 7830, 7850, 7870, 7890, 7910 and 7930 in this area .Stone has been found quite randomly for the entire level (Figure 4.21).
Hence, the area where wet holes have been found is somewhat same between these subsequent levels.
Few rings are about to shoot before completing production
Production has been completed
39
Figure 4.20 Map of instability for VR-954m (Data in Appendix A.12).
Figure 4.21 Map of instability for VR-978m (Data in Appendix A.13).
-1000 -980 -960 -940 -920 -900 -880 -860 -840 -820 -800
2450 2500 2550 2600 2650 2700 2750 2800 2850
wet holes
stone in hole redrilling
concrete in the hole
Y(m)
X (m)
VR-954
Hanging wall Foot wall
-1040 -1020 -1000 -980 -960 -940 -920 -900 -880 -860 -840
2450 2500 2550 2600 2650 2700 2750 2800 2850
wet holes
stone in the hole redrilling
concrete in the hole
Y(m)
X (m) VR-978
Hanging wall Foot wall
Most problematic zone
Approximate boundary of orebody Most problematic zone Approximate zone of orebody Mostly stone in the hole
40 4.5.2 VR-1002
On this level, blue dashed line includes more instabilities related with stones. Wet holes are dominating within red dashed line on this level from X= -900 m to X= -1060 m and from Y= +2600 m to Y= +2765 m (Figure 4.22).The drifts no. 7780, 7820,7840,7860,7880, 7900 and 7920 were situated in this area.
Figure 4.22 Map of instability for VR-1002m (Data in Appendix A.14).
4.5.3 Comparison among the sublevels
By comparing data from level 954 m to 1002 m, the area which is prone to instability with mostly wet condition ranges from X= -900 m to -1000 m and from Y= +2600 m to +2750 m in Vi-Ri (Figure 4.23). From this figure, it has also been concluded that instability increases towards the hanging wall side.
This comparison enables us to predict a fracture or jointed zone with water to flow through the sublevels.
Figure 4.24 shows a comparison of different instability problems among the sublevels where percentage of getting stone in the hole is increasing by slow rate and the re-drilling percentage has decreased from level 954 m to level 978 m and increased to 1.52% from level 978 m to level 1002 m.
This analysis is performed until 2012-05-10 and based on total number of holes* in each level.
Hence, Vi-Ri is affected by mostly stone in the holes and that might increase the number of re- drilling. There is also certain part which has been predicted as jointed or fractured rock mass more than the other part and it leads the water to pass through the sublevels.
-1080 -1060 -1040 -1020 -1000 -980 -960 -940 -920 -900
-8802400 2450 2500 2550 2600 2650 2700 2750 2800
wet hole
stone in the hole redrilling
concrete in the hole
Y(m)
X (m)
VR-1002
Hanging wall Foot wall
Most problematic zone Approximate zone of orebody Mostly stone in the hole
* Total boreholes which were blasted or charged since instabilities of boreholes are being recorded in production data just before charging.
