EMPIRICAL METHODS IN UNDERGROUND MINE DESIGN .empirical methods in underground mine design by rimas

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  • EMPIRICAL METHODS IN UNDERGROUND MINE DESIGN

    BY RIMAS PAKALNIS, Phd, P.Eng UBC EMERITUS PROFESSOR

    PAKALNIS & ASSOCIATES

  • 2

    TALK SUMMARIZES APPLICATIONS/IMPLEMENTATION OF EMPIRICAL DESIGN METHODS THAT HAS BEEN ESTABLISHED AT UBC / INDUSTRY OVER THE PAST 30 YEARS WITH OVER 170 UNDERGROUND OPERATIONS CONTRIBUTING EITHER THROUGH CONSULTING/RESEACH/DATABASE/VERIFICATION/IMPLEMENTATION

  • 3

    THE DESIGN PROCESS REQUIRES ALL THREE: NUMERICAL CODES, ANALYTICAL TOOLS AND OBSERVATIONAL TECHNIQUES AS TOOLS IN THE OVERALL DESIGN PROCESS WHICH INCORPORATE AN EMPIRICAL COMPONENT TOWARDS THE DESIGN

  • STRESS ANALYSIS

    FABRIC ANALYSIS

    ROCK MASS CLASSIFICATION

    INDUCED STRESS > ROCK MASS STRENGTH

    YIELD

    MODIFY GEOMETRY

    MODIFY MINING METHOD

    SUPPORT

    DESTRESS

    SEISMIC

    MONITORING

    OTHER

    ANALYTICAL DESIGNNUMERICAL MODELLING

    STRESS EFFECTEMPIRICAL DESIGN SOLUTION

    LIMIT SPAN

    SUPPORT WEDGE

    SEQUENCE

    OTHER

    EXCAVATION AND MONITORING

    RE-EVALUATE MINE PLAN

    BURST

    YESNO

    YESNO

    YES

    STRESS

    STRUCTUREROCK MASS

    IS STRUCTURE CONTROLLING STABILITY

    DESIGN METHODOLOGY INCORPORATING STRESS, STRUCTURE AND THE ROCK MASS

    4

  • 5

    KNOW THY DATA BASE AS EMPIRICAL DESIGN REQUIRES INTERPOLATION NOT

    EXTRAPOLATION!

    USE OF EMPIRICAL METHODS INHERENTLY MADE THESE SYSTEMS MORE RELIABLE AS THEY ARE REFINED/VERIFIED.

    EMPIRICAL METHODS ARE EVOLVING AND APPLICATION AT TIMES CONFUSING METHODS IN THIS TALK HAVE A STRONG ANALYTICAL FOUNDATION COUPLED WITH EXTENSIVE FIELD

    OBSERVATION TO ARRIVE AT A CALIBRATED EMPIRICAL APPROACH TOWARDS THE SOLUTION TO A GIVEN PROBLEM.

  • GEOMECHANICS DESIGN GROUP

    UB

    C M

    ININ

    G &

    MIN

    ER

    AL

    PR

    OC

    ES

    S E

    NG

    INE

    ER

    ING

    ROCK MASS

    CLASSIFICATION

    RMR (1976)

    Q - SYSTEM (1974)

    FOUNDATION

  • 7

    STOPE DESIGN

  • EMPIRICAL ESTIMATION OF WALL SLOUGH (ELOS) AFTER CLARK (1988).

    8

  • SURFACE ASSESSMENT FOR IRREGULAR GEOMETRY

    GENERALLY FOR OPEN STOPE WALL SURFACES THE RADIUS FACTOR IS 1.1 TIMES THE HYDRAULIC RADIUS IN MAGNITUDE FOR SPANS LESS THAN THREE TIMES THE HEIGHT.

  • CRITICAL SPAN CURVE FOR MINE ENTRY METHODS EMPLOYING LOCAL SUPPORT ONLY

    Stable Excavation no uncontrolled falls of ground. no movement of back observed no extraordinary support measures have been implemented.

    Potentially Unstable Excavation extra ground support may have been installed to prevent potential falls of ground movement within back increased frequency of ground working

    Unstable Excavation the area has collapsed failure above the back is approximately 0.5 x span in the absence of major structure

    support was not effective to maintain stability.

    10

    SPAN DESIGN

  • Pillar Class 1 Stable Pillar (FS>1.4)

    No sign of stress induced fracturing.

    Pillar Class 2 Unstable Pillar (1.21.4)

    Fracturing in corners only.

    Pillar Class 3 Unstable Pillar (1.11.2)

    Fracturing in pillar walls.

    Fractures < pillar height in length.

    Fracture aperture 1/2 pillar height

    in length. Fracture aperture > 5mm but less than 10mm.

    Pillar Class 5 Failed Pillar (FS 10mm, fractures throughout pillar.

    PILLAR DESIGN

  • PILLAR STABILITY GRAPH 12

  • CONDITIONS FOR A) GRAVITY FALL AND B) SLIDING INSTABILITY FOR WEDGE WITHIN BACK OF TUNNEL

    13

    FREE FALLING

    WEDGE

    BOND STRENGTH

    BOLT CAPACITY

    WFREE FALLING

    WEDGE

    BOND STRENGTH

    BOLT CAPACITY

    W

  • 14

  • FACTOR OF SAFETY ANALYSIS DEAD WEIGHT

    15

  • DEPTH OF FAILURE 0.5 X SPAN (RMR)

    CERRO LINDO-MILPO

  • SHOTCRETE AS CONFINING THE ROCK MASS INTO A SINGLE UNIT

    17

  • SUPPORT PROPERTIES

    18

  • Table 2. Fabric support requirements (after Grimstad and Barton, 1993) for 6m span.

    SURFACE SUPPORT (AFTER GRIMSTAD AND BARTON, 1993)

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  • INTERSECTION SUPPORT DEAD WEIGHT

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  • SCHEMATIC SHOWING TRANSITION OF WEAK ROCK MASS TO STRONGER AND EXISTING DATABASE.

    WALL STABILITY GRAPH AS DEVELOPED FOR WEAK ROCK MASSES (PAKALNIS, 2007)

    21

  • 1) STRENGTH R2 (25MPa) 4-2

    2) RQD 25% 8

    3) SPACING 50mm 5

    4) CONDITON SLT OPN TO OPN 12-6

    5) GRNWTR DRY 10

    RATING 39-31%

    STRUCTURE

    DESIGN 35%

    RMR CHARACTERIZATION MUDSTONE

  • 23

    25% RMR: 3.5m HR, 20m H X 12m UNDER 1m ELOS.

  • Figure 6c. RMR versus round advance at Queenstake (Pakalnis, 2007).

    LOADING OF 5M X 5M FACE AT BARRICK GOLDSTRIKE.

    Figure 6f. Effect of arching on back of tunnel

    24

  • 25

    ARCH IS CRITICAL

    PROFILE OF ARCH A2 PROFILE 5.2m WIDE X 6.2m HIGH (ARCHED BACK). DECLINE

  • PPV VERSUS SCALED DISTANCE FOR VARYING ROCK QUALITIES.

    26

  • 27

    Los crculos demarcados indican los barrenos de la tronadura anterior.

    Nunca se debe perforar donde existan perforaciones previas ya que pueden contener restos de explosivo

    Los nuevos barrenos estn indicados por la interseccin de las lneas de la grilla

    Preparado por: Cristin Cceres crstnccrs@yahoo.com

    1414 14 14

    1413

    13

    1313

    1313

    12

    12

    12

    10

    9889

    10

    10

    15151515

    15 15

    11

    9889

    74

    0

    7

    10

    6

    7

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    13

    610

    6

    10

    11

    7

    3

  • 28

    'HANDLED' RQD (HRQD) WAS INTRODUCED, ROBERTSON (1988). THE HRQD IS MEASURED IN THE SAME WAY AS THE RQD, AFTER THE CORE HAS BEEN FIRMLY HANDLED IN AN ATTEMPT TO BREAK THE CORE INTO SMALLER FRAGMENTS. DURING HANDLING, THE CORE IS FIRMLY TWISTED AND BENT, BUT WITHOUT SUBSTANTIAL FORCE OR THE USE OF ANY TOOLS. THIS ATTEMPTS TO QUANTIFY SOUND CORE.

    RQD THE ISRM(1978) DEFINITION: PIECES OF SOUND CORE OVER 10CM LONG THAT ARE EXPRESSED AS A PERCENTAGE OF THE LENGTH DRILLED.

    DEERE(1988) TO ONLY INCORPORATE GOOD ROCK RECOVERED FROM AN INTERVAL OF A BOREHOLE AND NOT TO INCLUDE PROBLEMATIC ROCK THAT IS HIGHLY WEATHERED, SOFT, FRACTURED, SHEARED AND JOINTED AND COUNTED AGAINST THE ROCK MASS. THE ISRM FURTHER IDENTIFIES MATERIAL THAT IS OBVIOUSLY WEAKER THAN THE SURROUNDING ROCK SUCH AS OVER CONSOLIDATED GOUGE IS DISCOUNTED AS IT IS ONLY ABLE TO BE RECOVERED BY ADVANCED DRILLING TECHNIQUES.

  • HANDLED RQD.

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  • DESIGN OF UNDERCUT SILL SPANS AS FUNCTION OF SILL MAT THICKNESS, UNCONFINED COMPRESSIVE STRENGTH AND STOPE SPAN.

    MINE %CEMENT SPAN SILL THICKNESS UCS COMMENTS REASON

    (m) (m) (MPa) UNDER FILL

    PASTE

    1 RED LAKE MINE 10 6.1 3 1.5 DESIGN STRENGTHS GOVERN TIME STRESS ~2000m DEPTH

    (~0.6m gap) TO MINE UNDER(14D-28D)

    2a ANGLOGOLD(1999 VISIT) 6.5 7.6 4.6 5.5 CRF WEAK RMR ~25%+

    2b MURRAY MINE 8% 9.1 4.6 6.9 CRF DESIGN

    2c (QUEENSTAKE-2004) 8% 21 4.6 6.9 MINED REMOTE - NO CAVE

    2" MINUS AGG

    GO UNDER A MIN OF 14D,

    WALL CRF 5-6% BINDER

    JAM TIGHT TO BACK/STEEP

    3 ESKAY 7 3 3 4 - 12 CRF(4MPa Design) WEAK RMR ~25%+

    UCS is 11MPa(28Day)

    4a TURQUOISE RIDGE 9 13.7 4 8.3 CRF TEST PANEL

    4b 9 3.7 3 8.3 CRF DRIFT & FILL WEAK RMR ~25%+

    4c 9 7.3 3 8.3 CRF PANEL

    5 MIDAS 7 2.7 3 3.4 CRF WEAK RMR ~25%+

    6 DEEP POST 6.75 4.9 4.3 4.8 CRF WEAK RMR ~25%+

    GO UNDER IN 28DAYS

    0.7 PASTE (FS=1.5)

    7a STILLWATER - NYE 10 1.8 2.7 0.3 GO UNDER IN 7DAYS-28DAYS)

    7b 2.4 2.7 0.5 (5% BINDER-0.5MPa UCS 28D)

    7c 3 2.7 0.7 (7% BINDER-0.7MPa UCS 28D) STRESS~ 800m

    7d 3.7 2.7 1 (10% BINDER-1MPa UCS 28D)

    7e 4.3 2.7 1.4 (12% BINDER-1.2MPa UCS 28D)

    7f 4.9 2.7 1.8

    7g 5.5 2.7 2.3

    7h 6.1 2.7 2.9

    8 MIEKLE STH 7 4.6-6.1 4.6 5.5 CRF WEAK RMR ~25%+

    BARRICK

    9 Gold Fields - AU 10 5 5 4.45 CRF WEAK RMR ~25%+

    10 Stratoni Mine 12.8 6-9 6 2 High Density Slurry WEAK RMR ~25%+

    TVX (78% WT SOLIDS)

    10% Cemented Hydraulic Fill

    11 Galena - Coeur de Alene 10 3 3 2.5 (73-75% Wt Solids) STRESS ~1000m DEPTH

    (includes 0.9m air gap) (UCS after 7 days)

    GO UNDER IN 3 DAYS(2.4MPa UCS)

    12 Lucky Friday - Hecla 8 2.4-4.6 3 4.8 8% Paste(COARSE TAILS) STRESS ~2000m DEPTH

    (Gold Hunter) (includes 0.6m air gap) (no free water)

    1.2MPa IN BACK AND 0.5MPa IN WALLS

    13 Newcrest 12-24 6-8 5 1.2-1.5 DESIGN STRENGTHS GOVERN TIME WEAK RMR ~25%+

    (Kencana Mine vs dry tuff TO GO UNDER PASTE 7D-28D

    SPAN 6m UNDER PASTE

    14 Lanfranchi Nickel Mines 4-8 6-12* 5 1.2-2 SPAN 12m INTERSECTIONS CABLED(6m) STRESS ~850m DEPTH

    (Helmuth South) *inters TO GO UNDER PASTE 14D

    GO UNDER IN 28 DAYS

    15 Cortez Hills 7.8 6-11* 4.6 6 SPAN IS 6m WITH 11m AT INTERSECTIONS WEAK RMR ~15%+

    (Barrick) *inters MAXIMUM TOP SIZE 5cm(2")

    CEMENTED AGGREGATE FILL

    16 Andaychagua Mine 14 5-15 3.5 16+ SPAN IS 15m WEAK RMR ~15%+

    (Volcan) AGGREGATE FILL -3/4"

    UNDERHAND CUT AND FILL MINING UNDER CEMENTED FILL

    UNDERHAND CUT AND FILL DATABASE 30

  • EMPIRICAL DATABASE OF FILL STRENGTH VS. SPAN WIDTH AFTER PAKALNIS ET AL. (2006)

  • MIN

    E%

    CE

    ME

    NT

    SP