A Journey of Support challenges at Saffy

Size: px

Start display at page:

Download "A Journey of Support challenges at Saffy"

Patricia Cameron
5 years ago
Views:

1 A Journey of Support challenges at Saffy Presented by: Christo Horn - Snr Manager Saffy Mike Kevane RE Manager Middelkraal 1 AMMSA 3 November 2011

2 Agenda Creating Context The PAST Managing Support Challenges The PRESENT Re-design and improve The FUTURE

3 Saffy Shaft Vertical Cross Section General Information: Depth m Levels - 10 Capacity - 200ktpm Reef tonnes Life of shaft years

4 Mining Changes: Past Present - Future Start Shaft Sinking Mechanised Mining XLP Mining Hybrid Mining Conventional miningmechanised cleaning Conventional Mining Conversion to Conventional 4

5 It s a journey Saffy LTIFR Threshold for 2012: Less than 3 x LTI s Per month 5

6 Mining Schedule and Layout N ±75 70 ±10m ±10m m 85

7 Rock Engineering INTRODUCTION Saffyshaft is located to the North of E1 Incline Shaft and has been sunk to a depth of 840 metres below surface (mbs). Original support design was aligned with the shallower E1 Incline Shaft, i.e. Saffy was designed to continue mining the deeper part of the orebody. Support design changed to cater for Mechanised Extra Low Profile (XLP Mining) The mine is currently reverting back to conventional stopingmethods, initially on a hybrid mining method on current levels using LHDs to clean the gullies, and then on a fully conventional mining method below current levels and further to the East and West of current stoping operations.

8 Geology of the Bushveld Igneous Complex N orth P O L O K W A N E Z E E R U S T R U ST E N B U R G P R E TO R IA L Y D E N B U R G J O H A N N E S BU R G L E G E N D Alkaline Complexes P IL A N E S BE R G G ranite, gra noph yre fels ite, leptite Upper Zone Upper Critical Zone and Main Zone Low e r Zone a nd Lower Critical Zone B ush veld ac id pha se R u stenb urg Layered Su ite B ush veld C o m ple x STEELPOORT FAULT S T E E L P O O R T Transvaal sequence Merensky Reef U G 2 Faults To w ns G R O B L E R S D A L R O O S S E N E K A L R U S T E N B U R G B R ITS P R E TO R IA STILLWATER IGNEOUS COMPLEX, Montana USA (To scale) S c a le in k ilo m e tre s

9 Lonmin Marikana Lease Area UG2 Mine Plan

10 Regional Faults & Dykes

11 Seismic Survey Update N ±80 ±10m ± ±10m 15W 16W 17W 17E 16E 15E ±10m 14W 14E 13W 13E 12W 11W 85 12E 11E 30m 10E

12 Scheduling around the Geology

Saffy Shaft Geology N ±50m wide Dyke on centre line of shaft, strikes NW-SE dips 75 West The zone with altered portion of

±75 75 ±10m ±75 ±5m 15W 14W 13W 16W 17W 17E 16E 70 ±10m 14E 13E 15E 30m 85 ±10m 15 Level East developed through 10m fault

13 Saffy Shaft Geology N ±50m wide Dyke on centre line of shaft, strikes NW-SE dips 75 West The zone with altered portion of HW1B Pyroxenite. Estimated extent =114106m W Stick buckling. Drilling and instrumentation program implemented. ±75 75 ±10m ±75 ±5m 15W 14W 13W 16W 17W 17E 16E 70 ±10m 14E 13E 15E 30m 85 ±10m 15 Level East developed through 10m fault and it is now back to normal Rail to reef 80 Cover hole intersected water on 13W approximately 20m before dyke, successfully sealed. 12W 11W 12E 10Level East intersected altered HW1B Pyroxenite zone affecting all developments from 16E raise. 11E 10E Area affected by Split reef= 8051m2 12 Level East Local Slump Structure as a result of numerous potholes between 11& 12 East.

14 Economic Reefs General Stratigraphy

15 Economic Reefs General Stratigraphy

16 Buckling of elongates

17 Geological features: Brows - Saffy 17

18 Opening up of joints

19 19

20 Pillar condition

21 PAST The predominant joint orientation (J1) is on strike with the joints containing a calciticfill and dipping towards the South at approximately 70 degrees. Another predominant joint set is orientated on dip (J2). The joint spacing is regular and approximately 3 m apart on both orientations. Opening of the joints were observed along both joint sets, even in close proximity to pillars. Domalfeatures were observed in most of the areas, although randomly orientated, dipping predominantly North. Panel inter-pillar spans varied between 24 m and 35 m.

22 Plan of affected area (10% of shaft reserves) and general geological trends

23 PRESENT Support standard and design strategy The in-panel support strategy for the shaft involves an integrated system which comprises of: Tendons: Cater for the 95% fall out thickness of 1.1 m. Current 1.6 m long Hydrabolts(friction anchored) have a 300 mm bond length requirement. Serve to clamp together and suspend the dead weight potential of key blocks defined by intersecting joints/structures to the height defined by historic fall of grounds (95%). Tendons are installed on a 1.5 m (dip) and 1 m (strike) spacing to accommodate the support resistance requirement, tendon load capacity (100 kn), joint spacing and face advance.

24 PRESENT Support standard and design strategy Timber: Pre-stressed timber elongates cater for the dead weight potential which exists as a result of the beam defined to the top of the UG2A markers (triplets) i.e. 8m. Hard gums with diameter range of 150 mm 170 mm and minimum loading capacity of 400 knare used (down rated to 267 knto account for lack of convergence). Elongates are installed at 0.6 m (dip) and 1.7 m (strike), the spacing needed for the support resistance requirement and scraper dimension.

25 Support standard and design strategy Grout Packs: High strength 16MPa (initially used on mechanised operations),750mm grout packs are used to cater for potential back breaks. In early 2011 it was decided to remain on the high strength mix as a result of instability problems reported. Packs are installed on a 6m x 6m spacing and used to be at a 18m maximum distance to face. The estimated pack strength at 28 days curing is approximately 500 tonnes. The pack layout grid acts purely as supplementary breaker line support. Below is an example of the parting that can occur along the HW1 Contact (Pyroxenite/Anorthosite interface) where weak sheared material is present.

26 HW1 Pyroxenite/ Anorthosite

27 PRESENT Support standard and design strategy Spans: Inter-pillar spans are designed using appropriate and applicable span analyses. Based on the beam thickness and behaviour, the Pyroxenitebeam to the 2A markers can be modelled as a Voussoirbeam as low angled structures are reinforced by instopetendons and the dip of the structures are predominantly above 70 degrees. For the material properties (Young s modulus, poisons ratio, stiffness) and parameters (beam thickness and geology) inter-pillar spans of 40 m are possible if an adequate in-stopesupport system is applied capable of providing the load resistance and compressive capabilities required for the selected span. Inter-pillar spans averaged 30 m.

28 PRESENT Support standard and design strategy Pillars: As previously mentioned an undulating clayey infill can be present along the top contact of the pillar and hanging wall contact. The impact of this weak material on the behaviour of the pillar has been studied and modelled to take account thereof. Observations confirm axial splitting rather than hour glassing (below). The pillar dimensions increase with depth and are proportional to a span increase / decrease (extraction related).

29 PILLARS Pillar behaviour - Hour glassing (left) vs. Axial splitting (right)

30 FUTURE The strategy and way forward involved investigations / interpretations that resulted in several remedial actions being immediately implemented to prevent further instabilities. Actual in-situ measurements are required to determine the exact behaviour of the rock mass in this area. Instrumentation and modelling is required to determine the actual behaviour of the rock mass for the current and future mining parameters.

31 Interpretation of behaviour in effected areas An overall assessment was conducted of the area to determine the assumed rock mass behaviour : Beam height From boreholes in the area it was established that the thickness of beam to the UG2A markers had increased from 8 m to 10.4 m and that the HW1 contact was at approximately 15 m. The support designed for the shaft was based on limited borehole information and Isopachdata which indicated the distance to the 2A markers at 8 m, More O Ferrall (2009).

32 Interpretation of behaviour in effected areas Structural geology and contours (10m)

33 UG2A Isopach N >8m 18 Level 17 Level >8m <8m <8m 16 Level 15 Level UG2A Isopach <8m 14 Level >8m <8m 13 Level 12 Level 11 Level >8m - U2 Beam greater than (>) 8m - U2 Beam less (<) 8m

34 Interpretation of behaviour in effected areas Rock mass behaviour The effected areas are the areas mining between two major dykes. The dykes by definition are younger in age and have intruded subsequent to the formation of the overall strata. As a result of the vertical intrusions, the area between the dykes would have been put into compression. The measured stress orientation on Saffyshaft indicated a high WNW-ESE stress oblique to the major regional geological structures and different from that experienced on the rest of Marikanawhere the prominent orientation is NNW-SSE. The ratio of horizontal to vertical stress is 1.8.

35 Interpretation of behaviour in effected areas Furthermore, the beam integrity would most likely be affected as a result of the beam cut-off due to the dyke intrusions. Below are indications of the probable hanging wall beam behaviour through the interaction of the dyke, jointing and horizontal planes.

36 Interpretation of behaviour in effected areas

37 Interpretation of behaviour in effected areas

38 REMEDIAL ACTIONS Based on the information presented, there are several aspects which must be taken into account to ensure the stability of the stopes. These include defining: Spans- Must account for structure and beam behaviour Support requirements and options Must account for beam height to markers, Must account for beam thickness to reinforce as a result of span, Must account for the interaction of the support units.

39 REMEDIAL ACTIONS Spans Pending more detailed in-situ measurements, the beam behaviour was modelled as a Cantilever and Voussoirbeam to estimate the amount of convergence expected vs. experienced in the panels. Observed underground convergence was estimated at between 10 cm 25 cm. The results indicated that thicker beams and smaller spans have less deflection. Where prominent joints or other regional low angle structures are present the intact hanging wall beam is cut off at one end and can be described as a cantilever beam. The critical span has been estimated at approximately 27 m when mining breast and approximately 50 m when mining down dip ( twice the panel span) from similar behaviour experienced at E3, du Plessis (Nov 2009). Under normal circumstances, inter-pillar spans of 30 m will be achievable based on a Voussoirbeam analysis. As the exact behaviour and amount of deflection is currently speculated, it was recommended to reduce the inter-pillar spansof all panels mining between the dykesto 27 mresulting in a 3 to 4% loss in extraction.

40 REMEDIAL ACTIONS Pillars The pillar size requirements are a function of panel spans and extraction. It was further recommended to leave pillars ahead of the mining faces before panels hole into the raiseswithin the pre-developed grid to ensure that strike spans are limited and additional stability is provided. The instrumentation will give information regarding the success and influence of these pillars.

41 REMEDIAL ACTIONS In-stope support requirements for 10.4m beam In-stope tendons: Current 1.6m Hydrabolts are of sufficient length. Resin bolting to be considered as an option. Timber elongates : To provide the SR of 32648kN/m 2 either single elongates spaced at 1.7 x 0.5m or double elongates spaced at 1.7 x 1m are to be considered. Grout packs : To increase the overall SR of the integrated system these are to be carried no more than 8m from the face and at a spacing of 6m x 4m. Alternatives to the RSS pack will be trialled.

42 PRESENT Support Standard

43 INSTRUMENTATION The installation of instrumentation is essential to determine the actual rock mass behaviour in response to mining. The following instrumentation programme was implemented : Extensometers Anchor above known partings to determine where movement is taking place in the hanging wall; Closure loggers measures convergence in response to mining (span) and rate of mining; Closure Robot acts as a warning device if abnormal (predefined) closure is taking place. The flashing lights will be an indication of the amount of closure should a panel be inaccessible; Stick load loggers will determine the load on an elongate. Can also be used to determine the load ate failure should the elongate fail.

44 INSTRUMENTATION Extensometers and Closure Logger

45 INSTRUMENTATION Closure Robot

46 INSTRUMENTATION Closure Logger Graph

47 MODELLING JBlock Key Block size distribution

48 MODELLING JBlock Keyblock size distribution and rock fall mode

49 MODELLING JBlock Hazard plot of keyblock falls

50 MODELLING JBLock JBLOCK results

51 In Summary Rock Engineering Mining Site specific design it s a journey. Understand your Rock Mass. Drilling programme with emphasis on holes. Dedicated drill rig for on reef holes. Update data base and related design. Numerical modelling. Instrumentation. Team work.with mining. Shiffiesand Miners to report immediately. Respect for RE department value-add. Sect.23 freedom to withdraw. It s still a business. Team work.with Tech Services

52 The FUTURE: Preventing FOG injuries 3 Million FOG FFS March Years 52

53 Saffy s Future?

54 Acknowledgement AMMSA Members for being here to share our learnings Lonmin Senior Management Gerrit van Rensburg, VP Middelkraal Michael Du Plessis Lonmin RE Group Manager JC Van Zyl Strata Control Officer Mike Kevane RE Manager Middelkraal Saffy team for withdrawing, reporting and working as a team Saffy s organised labour for support and understanding of our challenges Our Creator the many near misses which didn t result in fatalities

REVIEW OF FACE AREA SUPPORT FOR AMANDELBULT NO. 2 SHAFT AND SUBSEQUENT INTRODUCTION OF CABLE ANCHORS. L van Aswegen and S van Buuren.

REVIEW OF FACE AREA SUPPORT FOR AMANDELBULT NO. 2 SHAFT AND SUBSEQUENT INTRODUCTION OF CABLE ANCHORS. Abstract Rustenburg Platinum Mines, Amandelbult Section, part of the Anglo Platinum Group, is a platinum