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 (1.2<FS>1.4)
Fracturing in corners only.
Pillar Class 3 – Unstable Pillar (1.1<FS>1.2)
Fracturing in pillar walls.
Fractures < ½ pillar height in length.
Fracture aperture <5mm, increased corner spalling.
Pillar Class 4 – Unstable Pillar (1.0<FS>1.1)
Continuous, sub-parallel open fractures along pillar
walls. Start of hourglassing, fractures >1/2 pillar height
in length. Fracture aperture > 5mm but less than 10mm.
Pillar Class 5 – Failed Pillar (FS<1)
Extreme hourglassing. Major blocks fallen out.
Fracture aperture > 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)
19
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 círculos 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 están indicados por la intersección de las líneas de la grilla
Preparado por: Cristián Cáceres [email protected]
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
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.
29
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
AN
SIL
L T
HIC
KN
ES
SU
CS
CO
MM
EN
TS
RE
AS
ON
(m)
(m)
(MP
a)U
ND
ER
FIL
L
PA
STE
1R
ED
LA
KE
MIN
E10
6.1
31.
5D
ES
IGN
STR
EN
GTH
S G
OV
ER
N T
IME
STR
ES
S ~
2000
m D
EP
TH
(~0.
6m g
ap)
TO M
INE
UN
DE
R(1
4D-2
8D)
2aA
NG
LOG
OLD
(199
9 V
ISIT
)6.
57.
64.
65.
5C
RF
WE
AK
RM
R ~
25%
+
2bM
UR
RA
Y M
INE
8%9.
14.
66.
9C
RF
DE
SIG
N
2c(Q
UE
EN
STA
KE
-200
4)8%
214.
66.
9M
INE
D R
EM
OTE
- N
O C
AV
E
2" M
INU
S A
GG
GO
UN
DE
R A
MIN
OF
14D
,
WA
LL C
RF
5-6
% B
IND
ER
JAM
TIG
HT
TO B
AC
K/S
TEE
P
3E
SK
AY
73
34
- 12
CR
F(4
MP
a D
esig
n)W
EA
K R
MR
~25
%+
UC
S is
11M
Pa(
28D
ay)
4aTU
RQ
UO
ISE
RID
GE
913
.74
8.3
CR
F T
ES
T P
AN
EL
4b9
3.7
38.
3C
RF
DR
IFT
& F
ILL
WE
AK
RM
R ~
25%
+
4c9
7.3
38.
3C
RF
PA
NE
L
5M
IDA
S7
2.7
33.
4C
RF
WE
AK
RM
R ~
25%
+
6D
EE
P P
OS
T6.
754.
94.
34.
8C
RF
WE
AK
RM
R ~
25%
+
GO
UN
DE
R IN
28D
AY
S
0.
7P
AS
TE (
FS
=1.
5)
7aS
TILL
WA
TER
- N
YE
101.
82.
70.
3G
O U
ND
ER
IN 7
DA
YS
-28D
AY
S)
7b2.
42.
70.
5(5
% B
IND
ER
-0.5
MP
a U
CS
28D
)
7c3
2.7
0.7
(7%
BIN
DE
R-0
.7M
Pa
UC
S 2
8D)
STR
ES
S~
800
m
7d3.
72.
71
(10%
BIN
DE
R-1
MP
a U
CS
28D
)
7e4.
32.
71.
4(1
2% B
IND
ER
-1.2
MP
a U
CS
28D
)
7f4.
92.
71.
8
7g5.
52.
72.
3
7h6.
12.
72.
9
8M
IEK
LE S
TH7
4.6-
6.1
4.6
5.5
CR
FW
EA
K R
MR
~25
%+
BA
RR
ICK
9G
old
Fie
lds
- A
U
105
54.
45C
RF
WE
AK
RM
R ~
25%
+
10S
trat
oni M
ine
12.8
6-9
62
Hig
h D
ensi
ty S
lurr
yW
EA
K R
MR
~25
%+
TVX
(78%
WT
SO
LID
S)
10%
Cem
ente
d H
ydra
ulic
Fill
11G
alen
a -
Coe
ur d
e A
lene
103
32.
5(7
3-75
% W
t S
olid
s)S
TRE
SS
~10
00m
DE
PTH
(incl
udes
0.9
m a
ir ga
p)(U
CS
afte
r 7
days
)
GO
UN
DE
R IN
3 D
AY
S(2
.4M
Pa
UC
S)
12Lu
cky
Frid
ay -
Hec
la8
2.4-
4.6
34.
88%
Pas
te(C
OA
RS
E T
AIL
S)
STR
ES
S ~
2000
m D
EP
TH
(Gol
d H
unte
r)(in
clud
es 0
.6m
air
gap)
(no
free
wat
er)
1.2M
Pa
IN B
AC
K A
ND
0.5
MP
a IN
WA
LLS
13N
ewcr
est
12-2
46-
85
1.2-
1.5
DE
SIG
N S
TRE
NG
THS
GO
VE
RN
TIM
E
WE
AK
RM
R ~
25%
+
(Ken
cana
Min
evs
dry
tuf
f
TO G
O U
ND
ER
PA
STE
7D
-28D
SP
AN
6m
UN
DE
R P
AS
TE
14La
nfra
nchi
Nic
kel M
ines
4-
86-
12*
51.
2-2
SP
AN
12m
INTE
RS
EC
TIO
NS
CA
BLE
D(6
m)
STR
ES
S ~
850m
DE
PTH
(Hel
mut
h S
outh
)*i
nter
s
TO G
O U
ND
ER
PA
STE
14D
GO
UN
DE
R IN
28
DA
YS
15C
orte
z H
ills
7.8
6-11
* 4.
66
SP
AN
IS 6
m W
ITH
11m
AT
INTE
RS
EC
TIO
NS
WE
AK
RM
R ~
15%
+
(Bar
rick)
*int
ers
M
AXI
MU
M T
OP
SIZ
E 5
cm(2
")
CE
ME
NTE
D A
GG
RE
GA
TE F
ILL
16A
nday
chag
ua M
ine
145-
153.
516
+S
PA
N IS
15m
WE
AK
RM
R ~
15%
+
(Vol
can)
AG
GR
EG
ATE
FIL
L -3
/4"
UN
DE
RH
AN
D C
UT
AN
D F
ILL
MIN
ING
UN
DE
R C
EM
EN
TE
D F
ILL
33
ANDAYCHAGUA-15m SPAN (PERU)
RED LAKE MINE – 6m SPAN (CANADA)
KENCANA MINE – 6m SPAN (INDONESIA)
MURRAY MINE – 12m SPAN (USA)
STILLWATER MINE STABLE UNDERCUT PASTE SPANS VERSUS RECORDED UCS WITH BEAM FORMULAE DESIGN CURVES FOR 3m THICK MAT.
EFFECT OF FREEZING ON RMR76 (ROWORTH, 2013).
36
37
McARTHUR MINE – CAMECO CANADA
38
KUOPOL MINE – KINROSS RUSSIA
39
4ft ADVANCE4ft ADVANCE4ft ADVANCE4ft ADVANCE
42
1974 CMJ
USE COMMON SENSE BACK UP WITH ENGINEERING
SUDBURY MINES
We are especially interested in the change of apparent strength with changing W:H, and the changing mode of failure. Increasing the width restrains the core of a pillar. Even dust will support a load if wide enough. Slide #4. W:H = 1:2, tall and thin, failed around 2148 psi, by splitting, in tension - the weakest mode of failure. Slide #5. W:H = 1:1, square, failed on a 45 degree shear, at 3460 psi. Slide #6. W:H =2:1, failed in shear at 3420 psi. Slide #7. W:H = 2:1, failed at 5060 psi, with shear going into ”roof”. Slide #8. W:H = 4:1, failed at 7017 psi, shearing both pillar and roof. Slide #9. W:H = 8:1, wide pillar. Failed at 13280 psi, both roof and pillar. This was their typical pillar shape. Slide #10. W:H = 16:1. Both roof and pillar failed at 17,900 psi. You might say that trona is a pretty strong rock … VITAL CONCLUSION IS THAT IF PILLAR IS WIDE ENOUGH, THUS STIFF ENOUGH, IT WILL PUNCH INTO ROOF AND/OR FLOOR. THEREFORE IN MOST MINES A DIFFERENT APPROACH TO PILLAR DESIGN IS NEEDED. TO PRESERVE THE MINE OPENING THE PILLARS MUST YIELD A LITTLE, AND THAT IS CONTROLLED MORE BY W:H RATIO AND LOCAL CONDITIONS THAN BY LAB TESTS AND FORMULAS.
1974 CMJ
44
THINK LIKE THE ROCK!
PENSAR COMO LA ROCA!
EVOLUTION OF APPLIED ROCK MECHANICS IN THE GLOBAL MINING INDUSTRY – DESIGN TOOLS
LA EVOLUCIÓN DE LA MECÁNICA DE ROCAS APLICADA EN LA
INDUSTRIA MINERA GLOBALIZADA – HERRAMIENTAS DE DISEÑO
THE ROOF IS FALLING
El techo se derrumbe
ANTES "PREDECIR DERRUMBE - NO DERRUMBE" - MECÁNICA DE ROCAS HOY "PREDECIR DERRUMBE - DERRUMBE" - EMPÍRICO
GEOMECHANICS DESIGN GROUP
UB
C M
ININ
G &
MIN
ER
AL
PR
OC
ES
S E
NG
INE
ER
ING
CONCLUSIONS
CALIBRATION TO ANALYTICAL AND EMPIRICAL APPROACHES
MODIFIED ACCORDING TO MINE BEHAVIOUR
SAFETY & WORKABLE
48
GRACIAS!
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