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

EMPIRICAL METHODS IN UNDERGROUND MINE DESIGN

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

PAKALNIS & ASSOCIATES

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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

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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

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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

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STOPE DESIGN

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

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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.

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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

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FREE FALLING

WEDGE

BOND STRENGTH

BOLT CAPACITY

WFREE FALLING

WEDGE

BOND STRENGTH

BOLT CAPACITY

W

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FACTOR OF SAFETY ANALYSIS DEAD WEIGHT

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DEPTH OF FAILURE 0.5 X SPAN (RMR)

CERRO LINDO-MILPO

SHOTCRETE AS CONFINING THE ROCK MASS INTO A SINGLE UNIT

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SUPPORT PROPERTIES

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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)

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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

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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

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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.

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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

6

4

2

13

610

6

10

11

7

3

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'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