Anvendt Bergmekanikk 10/01/2018 PRAKTISKE EKSEMPLER FRA ANVENDT BERGMEKANIKK I GRUVEINDUSTRIEN. Nghia Trinh SINTEF Byggforsk

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1 Anvendt Bergmekanikk 10/01/2018 PRAKTISKE EKSEMPLER FRA ANVENDT BERGMEKANIKK I GRUVEINDUSTRIEN Nghia Trinh SINTEF Byggforsk

2 Presentation content 1. SINTEF in mining industry 2. Activities at Rana Gruber 3. Activities at a high stress mine 4. SINTEF philosophy 2

3 SINTEF in mining industry 3 Skaland Graphite Franzefoss Miljøkalk As Sala Mineral Norcem Boliden Mineral Glærum Kalksteinsbrudd Store Norske Coal Naas Kalkstein Norcalsitt Rana Gruber Industrimineraler North Cape Minerals Hustad Group Hammerfall IMM EU research Brønnøy Kalk AS Sweden Sweden Spitsbergen Italy Lundhs Labrador Björka Mineral Sweden Grong Gruber J. Grønseth Nikkel & Olivin Skaland Grafit Sydvaranger Fauskemarmor Norwegian Talc Gudvangen Stein Norstone Folldal Verk Falkhammar Magn Fosdalen Mining Bleikvassli Mines Dannemora Mine Sweden Orkla Mining Gränges Elkem Skorovas Elkem Tana Sulitjelma Mining Minnor Minerals Greenex Mines Titania Mines Arna Knuseverk Rautarukki OY Rødsand Mining Franzefoss Røros Copper Rio Tinto Mines LKAB Coricancha and Contonga Sweden Greenland Finland Spain Sweden Peru

4 SINTEF in mining industry Typical activities for a mining project (open pit and underground) may consist: Stress measurement hydraulic fracturing, 2D and/or 3D with self development method; Deformation, stress, and groundwater monitoring; Laboratory tests rock properties; Numerical modelling in combination with measurement and monitoring to provide a reliable tool for planning; 4 Engineering geological mapping; A projects are normally followed for many years.

5 SINTEF in mining industry WATER INJECTION TEST FROM SURFACE: HIGH PRESSURE DATA PUMP LOGGING REEL DRUM TESTING; ORIENTATION OF FRACTURE; DRILLHOLE; Diam mm, DEPTH MAX. 300 m FRACTURE S T R A D D L E P A C K E R IMPRESSION TEST PACKER SECTION COMPASS 5

6 SINTEF in mining industry In situ rock stress measurements (2D and 3D) Rock laboratory tests Numerical modelling of different mining alternatives Installation of the monitoring: extensometers and stress sensor Following up 6

7 7 Activities at Rana mine

stoping => Vertical and horizontal pillars are existed; Before the sub-level caving

8 Application at Rana mine A major challenge in this mine is very high horizontal stresses Verify with the current situation The previous mining method is sublevel stoping => Vertical and horizontal pillars are existed; Before the sub-level caving can start, the pillars need to be removed => Check stability of the footwall; 250 m.a.s.l 8

9 Application at Rana mine After removing the pillar, the mine will be developed in 4 mining levels: 221 ; 187 ; 153 ; m.a.s.l 250 m.a.s.l 221 m.a.s.l 187 m.a.s.l 153 m.a.s.l m.a.s.l

10 Application at Rana mine Consequences of uneven caving front? Optimum distance between drifts? Consequences of changing shape? 2 1 Option 1: Mining one level at a time Planned

11 Application at Rana mine Mining all level: Option 2: Mining many levels at a time Planned

12 Application at Rana mine Consequences of uneven caving front? Optimum distance between drifts? Consequences of changing shape? Option 3: Mining from centre first

13 Application at Rana mine A 3D-model was established with proper simplification; Different mining alternatives were tested to find advantages and disadvantages.

14 Application at Rana mine Stress monitoring: using 2D-long-term-door-stopper 14

15 Application at Rana mine Installed equipment for monitoring and verification: Felt ort 2D Langtidsdoorstopper Borort 5 Ekstensometer Nivå 221 m Nivå123 m 2D Lantidsdoorstopper Verksted 2D Langtidsdoorstopper Nivå 221 borort 5 2D Langtidsdoorstopper Nivå 130 Kantine Legend Extensometer Long term 2D-stress sensor 15

16 Application at Rana mine Case 1: Result of the SINTEF's measurement - verification: MPa 250 m MPa 221 m

17 Application at Rana mine Stress in a pillar and verification: 35 MPa 45 MPa 20 MPa 17

18 Application at Rana mine Recorded displacement in the extensometer 250 vs numerical model: 18

19 Application at Rana mine Summary activities in Rana mine: 1. Many stress measurements and laboratory tests have been carried out by SINTEF over the years (since 1977). A good rock mechanics database was created from this; 2. Different models (2D, 3D-simplified, and 3D-total model) was established based on the need and complexity of the issues to be studied; 3. Stress monitoring and displacement monitoring equipment have been installed at key locations for monitor the safety of the mine, and also providing information for calibration and verification of the numerical model, so that the model becomes a reliable tool for planning. 24

20 25 Activities at a high stress mine

21 26 What is a "high stress" situation?

"High stress" does not always mean "negative" "High stress" can be utilised in this mine to make a large span room; To make this possible, it is necessary to know the

22 "High stress" does not always mean "negative" "High stress" can be utilised in this mine to make a large span room; To make this possible, it is necessary to know the stress orientation and magnitude ; One should also note that geological structural (faults, fold,..) may affect the orientation and magnitude of in-situ stress locally. 27

23 28 But, yes, "high stress" gives some challenges

24 29 Some rock falls

25 30 Some rock falls

26 Very tough questions 1. Why it happened here, not other locations? 2. Where could be the next? Can he ask easier questions? 31

27 Presentation 1. Mapping area 2. "Generally Stable" pillars 3. "Minor/Medium Slabbing" pillars 4. "Unstable" pillars 5. Thin wall a hidden danger 6. "Next" rock fall 7. Rock support bolt performance 8. Comments for this mine 9. "Tripod" over the years 32

28 1. Mapping area Location for the mapping is within the red marked area; A total of 41 pillars was mapped; Mapped pillars were divided into 3 groups: "Green", "Yellow" and "Red" based on observed condition Drift 10 Drift 16 Drift 14 Drift 12 Drift 18 Drift 20 Drift 22 33

$group are in overall showing a stable situation: Very minor slabbing, local fractures, or few individual unfavourable joints are$ $observed; Slabbing, fractures, and joints are local, no risk of further development that could lead to a gradual, progressive$

29 2. "Generally Stable" pillars Green Group Typical pillars without instability concern: "Generally Stable" group: pillars in this group are in overall showing a stable situation: Very minor slabbing, local fractures, or few individual unfavourable joints are observed; Slabbing, fractures, and joints are local, no risk of further development that could lead to a gradual, progressive failure. No systematic rock support is required except spot bolting needed to keep the pillar supporting the roof of the mine in a long term. 34

3. "Minor/Medium Slabbing" pillars Yellow Group Typical pillars with instability concern (10-12/05):

$Significant fractures are observed.$ in a long term; Rock slabbing appears in various degree from a noticeable to a significant area of

30 3. "Minor/Medium Slabbing" pillars Yellow Group Typical pillars with instability concern (10-12/05): "Minor/Medium Slabbing" group: pillars in this group expose an uncertain stability situation: 35 Significant fractures are observed. The fractures may lead to a potentially unstable situation in the pillar and rock support is required in a long term; Rock slabbing appears in various degree from a noticeable to a significant area of the pillar: Working directly under the area is not recommended. Additional rock support measures is be required before working directly under an area with minor/medium slabbing;

31 3. "Minor/Medium Slabbing" pillars Yellow Group Typical pillars with instability concern (14-18/05): 36

4. "Unstable" pillars Red Group Typical pillars serious instability problem

slabbing occurs in a very large part of the pillar.

32 4. "Unstable" pillars Red Group Typical pillars serious instability problem (10-12/09): "Unstable" group: pillars in this group expose an unstable situation. The following descriptors have been used for pillars in this group: Rock slabbing occurs in a very large part of the pillar. The slabbing leads to a progressive destabilisation and the pillar will eventually collapse; Rock fall may take place uncontrolled; Working directly under "Unstable Pillar" area is prohibited; 37

33 4. "Unstable" pillars Red Group Typical pillars serious instability problem (12-14/02): 38

34 4. "Unstable" pillars Red Group Typical pillars serious instability problem (12-14/06): 39

35 5. Thin wall a hidden danger Thin wall and its apparent condition: 40

36 6. "Next" rock fall Location with risk of the "next" rock fall: 12-14/07 41

37 6. "Next" rock fall Location with risk of the "next" rock fall:? 18-20/03 42

38 6. "Next" rock fall Location with risk of the "next" rock fall: 12-14/05 in the "Yellow" group, whereas L-per is only 4 m???? With this small L-per it is expected a severe instability condition in the pillar. Why it appears as on in "Yellow" group?? One explanation for the better stability situation than expected could be that the shape of this pillar is complicated. The measurement we made may not be accurate enough to capture the real situation; The pillar shows an useful information that the "Medium slabbing" area appears at the part with smaller L-per /05? 43

39 7. Rock support bolt performance Bolt in a high stress condition: 44

40 7. Rock support bolt performance Bolt in a high stress condition: 45

41 7. Rock support bolt performance Bolt in a high stress condition: 46

42 7. Rock support bolt performance Bolt in a high stress condition: 47 In a normal underground structure, it is best to use shotcrete in this situation, but not at this mine

43 7. Rock support bolt performance Bolt in a high stress condition: Steel mesh may be an alternative to provide a confinement.. 48

44 7. Rock support bolt performance Bolt in a high stress condition: Steel straps are not really suitable to provide a confinement. 49

45 7. Rock support bolt performance Steel straps may be more suitable for supporting individual rock block: 50

46 7. Rock support bolt performance Thin shotcrete should be avoided: 51

47 7. Rock support bolt performance Thin shotcrete should be avoided: 52

48 8. Comments for this mine 1. Why it happened here, not other locations? 2. Where could be the next? Answer for question 1: Most likely the over-stressed in thin pillar is the reason for the rockfall in that particular location; Answer for question 2: Pillar 12-14/07 could be a next rock fall area - need more thoroughly measurement and observation; Pillar size in the new area can be designed at 12x12 m; Rock support should be improved; Blasting quality near the pillar should be improved; Thin rock wall is strongly NOT recommended; 53

49 54 8. Comments for this mine

50 55 8. Comments for this mine

51 9. Activities over the years We carried out stress measurement to find in-situ stress; We carried out numerical model with stress measurement; We recommend to install stress monitoring equipment (Long Term Door Stopper Monitoring - LTDM) at some important locations. 56

52 9. Activities over the years We carried out stress measurement to find in-situ stress; We carried out numerical model with stress measurement; We recommend to install stress monitoring equipment (Long Term Door Stopper Monitoring - LTDM) at some important locations. 57 How much stress this rock can tolerate before it collapses?

53 9. Activities over the years We carried out stress measurement to find in-situ stress; We carried out numerical model with stress measurement;; We recommend to install stress monitoring equipment (Long Term Door Stopper Monitoring - LTDM) at some important locations. 58

54 SINTEF philosophy We believe that we can use a "tripod" of information to solve many rock mechanics challenges. The "Tripod" consists of: In situ rock stress measurements (2D and 3D) Rock laboratory tests Numerical modelling 2D 3D 59 Installation of the monitoring: extensometers and stress sensor Following up

55 SINTEF philosophy Visual observation Monitoring equipment In-situ rock stress Rock mass quality Numerical Analyses Verification Control and improve the model Use the model as a forecasting/planning tool 60

56 Teknologi for et bedre samfunn

IN-SITU ROCK STRESS MEASUREMENTS

111 1 IN-SITU ROCK STRESS MEASUREMENTS Brief description of methods applied by SINTEF Practical applications Lists of clients Updated Sep. 2007 SINTEF Building and Infrastructure Rock and Soil Mechanics