Geomechanics Class System Laubscher Jul 2009

8/20/2019 Geomechanics Class System Laubscher Jul 2009

1/17

J

S.

Atr Inst Min Metal/

vol. 90, no. 10.

Qct. 1990. pp.

257-273.

A geo~echanics l ssifi tion system for the

r ting of ro k m ss in m ine design

by D .H . LAUBSCHER *

SYNOPSIS

T he m ining rock-m ass rating M AM A) classification system w as introduced in 1974 as a developm ent of the C S IA

g eom ec ha nics c la ss ific atio n s ys te m to c ater fo r d iv ers e m in in g s itu atio ns. T he fu nd am enta l d iffe re nce w as th e re co gni-

tio n th at i n s it u rock-m ass ratings A M A ) had to be adjusted according to the m ining environm ent so that the final

ratings M AM A) could be used for m ine design. T he adjustm ent param eters are weathering, m ining-induced stresses,

joint orientation, and blasting effects.

It is also possible to use the ratings A M A ) in the determ ination of em pirical rock-m ass strength A M S ) and then

in the application of the adjustm ents to arrive at a design rock-m ass strength D A M S ). T his classification system

is versatile, and the rock-m ass rating A MA ), the m ining rock-m ass rating M AM A), and the design rock-m ass strength

DA M S ) provide good guidelines for the purposes of m ine design. H ow ever, in som e cases a m ore detailed in-

vestigation m ay be required, in w hich case greater attention is paid to specific param eters of the system .

N arrow and w eak geological features that are continuous w ithin and beyond the stope or pillar m ust be identified

a nd ra te d s ep ara te ly .

T he paper describes the procedure required to arrive at the ratings, and presents practical exam ples of the

application of the system to m ine design,

S AM EV A T TIN G

D ie m ynrotsm assa-aanslag-klassifikasiestelsel M A M A) is in 1974 ingevoer as n

ontw ikkeling van die W NN A

s e g eo me gan ik ak la ssifik as ie stels el o m v ir u itee nlo pe nd e m yn bo uto es tan de v oo rs ie nin g te m aa k, D ie fu nd am ente le

verskil w as die erkenning van die feit dat

s itu -ro ts ma ss a-a an sla e A M A) v olg en s d ie m yn bo u-o mg ew in g a an ge su iw er

m oes w ord om die finale aanslae M A M A) vir m ynontwerp te kan gebruik, D ie aansuiw eringsparam eters is ver-

w ering, m ynbouge induseerde spannings, naatorientasie en die gevolge van skietw erk,

D it is ook m oontlik om die aanslae A M A ) by die bepaling van em piriese rotsm assasterkte A M S ) te gebruik,

en dan by die toepassing van aansuiw erings om

n

o nt we rp ro ts m as sa st er kt e D A M S) t e k ry , H ie rd ie k la ss if ik as ie ste ls el

is v ee lsy dig e n die ro ts ma ss a-a an slag A MA ), d ie m yn ro ts ma ss a-a an sla g M AM A), e n d ie on tw erp ro tsm as sa ste rk te

D AM S) verskaf goeie riglyne vir die doeleindes van m ynontw erp, D aar kan egter in som mige gevalle

n

uitvoeriger

ondersoek nodig w ees w aarin daar m eer aandag aan spesifieke param eters van die stelsel geskenk w ord.

S m al en sw ak geologiese aspekte w at deurlopend is in en verby die afbouplek of pilaar, m oet ge identifiseer en

afsonderlik aangeslaan w ord,

D ie referaat beskryf die prosedure wat nodig is om die aanslae te kry en gee praktiese voorbeelde van die toepassing

v an d ie ste ls el o p m yn bo u-o ntw erp ,

INTRODUCTION

The classification system know n as the m ining rock-

m ass rating (M RMR) system was introduced in 1974 as

a d evelopm en t of th e CSIR g eom ech anics classific atio n

system l,2. The development is based on the concept of

in situ

and adjusted ratings, the param eters and values

being related to com plex m ining situations. Since that

t ime , th er e have been modif ic at ions and imp rovemen ts3 -S ,

a nd th e system h as b een used su ccessfu lly in m ining pro-

jects in C anad a, C hile, th e P hilip pin es, S ri L an ka, S ou th

A frica, the USA, and Zim babwe.

T his p ap er c on so lid ate s th e work p re se nte d in p re vio us

paper s and des cri be s t he bas ic p ri nc ip le s, d at a-coll ec tion

procedure, calculation of ratings (RMR ), adjustm ents

(MRMR ), d esign rock-m ass stre ngth (DRMS), an d prac-

tical application of the system s.

An impo rta nt d ev elo pmen t o f th is c la ssific atio n mak es

it suitable for use in the assessm ent of rock surfaces, as

w ell as borehole cores.

T ay lo r4 r ev iewed the c la ss if ic ati on s ys tems developed

by W ickham, Barton, Bieniawski, and Laubscher and

.

A ssociate C onsultant, Steffen, Robertson K irsten Inc., 16th Floor,

2 0 A nde rso n S tree t, Jo ha nn esb urg , 2 00 1.

@

T he South A frican Institute of M ining and M etallurgy, 1990. SA

IS SN 0038-223X /3.00 + 0.00. P aper received 3rd A pril, 1989.

concluded that

Thus, the four system s chosen as being the m ost advanced classifica-

tions are based on relevant param eters. E ach technique undoubtedly

yields meaningful results, but only Laubscher s geomechanics

classification and the Q

system of B arton offer suitable guidelines

for the assessment of the main parameters; namely, the joint attri-

butes. For general m ining usage and where the application of a

c la ssific atio n v arie s w id ely , L aub sc he r s g eo me cha nic s c la ssific atio n

has the added advantage of allow ing further adjustm ents to the rating

for different situations. This, coupled with the fact that the tech-

nique has been in use for six years, gives no reason for changing

to another system which offers no substantial improvement.

The figure below shows a 98 per cent correlation

between the RMR of the MRMR system and the NO I

system based on the classification by Taylor4 of thirty

sites ranging from very poor to very good. Thus, if NOI

data are available, this information can be used in the

pract ical applicat ions.

PRINCIPLES

A classification system m ust be straightforw ard and

have a strong practical bias so that it can form part of

t he norma l g eo logic al and rock-mechan ic s i nvest ig ations

to be used for mine design and communication. H ighly

sop histicated techn iq ues are tim e-consuming , and m ost

JO UA NA L O F T HE S OU TH A FA IC AN IN STIT UT E O F M IN IN G A ND M ET ALLU AG Y

O CT OB EA 1 99 0

25 7


2/17

80

,....

60

.

RMR/MRMR

40

20

0

100

90

80

70

60

; .

50

:.:

u

0

40

a::

~«

30

w

~2 0

10

0

0,01

1,0

10,0

100,0 1000,0

,1

Q System

m ines cannot afford the large staff required to provide

co mp lex data of d oub tful b enefit to the p lan nin g and pro-

duct ion departmen ts .

T he approach adopted involves the assignm ent to the

rock mass of an

in situ

rating based on m easurable

geological param eters. Each geological param eter is

w eighted according to its im portance, and is assigned a

m axim um rating so that the total of all the param eters

is 1 00 . T his w eigh tin g w as review ed at reg ular intervals

in the developm ent of the system and is now accepted

as being as accurate as possible. The range of 0 to 100

is used to co ver all variation s in jointed roc k m asses from

v ery po or to very go od. T he classification is divid ed into

five classes with ratings of 20 per class, and w ith A and

B sub-divis ions.

A colour schem e is used to denote the classes on plan

and section: class 1 blue, class 2 green, class 3 yellow,

class 4 brow n, and class 5 red. C lass designations are for

general use, and the ratings should be used for design

purposes.

T he ratings are, in effect, the relative strengths of the

rock m asses. T he acc ura cy o f the classification dep end s

on the sam pling of the area being investigated. The ter-

minology

preliminary intermediate

an d

final

sh ould be

a pp lie d to a sse ssmen ts to in dic ate th e sta te o f d rillin g a nd

developm ent. It is essential that classification data are

m ade available at an early stage so that the correct deci-

sions are m ade on m ining m ethod, layout, and support

requirements.

In the assessm ent of how the rock m ass will behave

in a m ining environm ent, the rock-m ass ratings (R MR )

are adjusted for w eathering, m ining-induced stresses,

joint orientation, and blasting effects. The adjusted

ratings are called the mining rock-mass ratings or

MRMR.

It is also possible to use the ratings to determine an

em pirical rock-m ass strength (RM S) in m egapascals

(M Pa). T he i n s it u ro ck -mass stre ng th (RMS) is a dju ste d

as above to give a design rock-m ass strength (DRM S).

T his figure is extrem ely useful w hen related to th e stress

en viron me nt, and h as b een used fo r m ath em atical m odel-

ling.

The c la ss ifi ca tio n s yst em is v er sa til e, a nd t he ro ck -mass

ra tin g (RMR), th e m in in g ro ck -mass ra tin g (MRMR), a nd

the design rock-mass strength (DRM S) provide good

guidelines for m ine design purposes. H ow ever, in som e

cases w here a m ore detailed investigation is required,

e xamp le s o f th ese situ atio ns a re d esc rib ed in whic h sp ec i-

fic param eters of the system are used.

25 8

OCTOBER 1 99 0

JO URNA L O F TH E SOU TH A FR IC AN IN ST ITU TE O F M IN IN G AND META LL URGY

S in ce a ve ra ge v alu es c an b e m isle ad in g a nd th e w eake st

zo nes m ay de term ine the resp onse o f the w hole rock m ass,

these zones m ust be rated on their ow n. N arrow and w eak

g eo lo gic al fe atu re s th at a re c on tin uo us w ith in a nd b ey on d

th e sto pe o r p illa r must b e id en tifie d a nd ra te d se pa ra te ly .

GEOLOGICAL PARAMETERS, SAMPLING , AND RATINGS

The geological param eters that m ust be assessed include

the intact rock strength (IRS), joint/fracture spacing, and

joint condition/water. Before the classification is done,

the core or rock surface is examined and divided into

zones of similar characteristics to which the ratings are

then applied. These parameters and their respective

ratings are shown in Table I.

Intact R ock Strength (IR S)

The IRS is th e uncon fin ed uniaxi al comp re ss iv e s treng th

of the rock betw een fractures and joints. It is im portant

to n ote that the cores se lecte d fo r te stw ork a re inv ariably

the strongest pieces of that rock and do not necessarily

reflect th e av era ge values; in fact, o n a larg e copp er m ine ,

only unblem ished core w as tested. The IR S of a defined

zone can be affected by the presence of w eak and strong

intact rock, which can occur in bedded deposits and

deposits of varying m ineralization. A n average value is

assigned to the zone on the basis that the weaker rock

w ill have a greater influence on the average value. The

relationship is non-linear, and the values can be read off

an em pirical chart (Fig. 1).

SELECT CURV E U SING W EA K RO CK

IRS AS% OF STRONG ROCK IRS

10% 20% 30% 40 . 50 10 60% 70% 80 1. 9O Y.

10

20

AVERAGE IRS AS % OF

STRONG ROCK IRS

F ig.1 D eterm ination of average IA S w he re the rock m ass con

tains weak and strong zones

Example:

Strong rock IAS

=

1 00 MPa

W eak rock IAS

=

20 M Pa

W eak rock IAS x 100

=

20

Strong rock IAS

W eak rock IAS

=

45

A ve ra ge IA S

=

37 of 100 M Pa

=

37 M Pa


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The rating range is from 0 to 20 to cater for specim en

strengths of 0 to greater than 185 M Pa. The upper limit

of 18 5 M Pa h as be en se lecte d beca use IR S v alu es g reater

th an th is have little b earing on the streng th o f jointed ro ck

masses.

Spacing of Fractures and Joints (RQD+JS or FF)

Sp acin g is th e m easurem ent of all the d iscon tin uities

and partings, and does not include cem ented features.

Cemented features affect the IRS and as such must be

included in that determ ination. A joint is an obvious

feature that is continuous if its length is greater than the

width of the excavation or if it abuts against another

joint, Le. joints define blocks of rock. Fractures and

p arting s do not n ecessarily hav e co ntinu ity . A max imum

of three joint sets is used on the basis that three joint sets

w ill define a rock block; any other joints w ill merely

m odify the shape of the block.

Two te ch niq ue s h av e b ee n d ev elo pe d fo r th e a sse ssmen t

o f th is p arame te r:

. the more detailed technique is to measure the rock

quality desi~nation (RQD) and joint spacing (JS)

separately, the maximum ratings being 15 and 25

respectively;

. th e o ther techn iqu e is to m easure all th e d iscon tin uities

and to re cord th ese as the fractu re freq uency p er m etre

(FF/m ) with a m axim um rating of 40, Le. the 15 and

25 from above are added.

Designation of Rock Quality RQD)

The R QD determ ination is a core-reco very tech nique

in which only cores with a length of more than 100 m m

are r ecord ed :

RQ D, 0,10

=

Total lengths of core> 100 m m

x 100.

Length of run

Only cores of at least BX M size (42 m m) should be used.

It is also essential that the drilling is of a high standard.

T he orientation of th e fractures w ith respect to th e core

is impo rta nt fo r, if a BXM bore ho le is d rille d p erp en dic u-

lar to fractures spaced at 90 m m, the RQD is 0 per cent.

If the bore hole is drilled at an inclination of 40 degrees,

th e spacing betw een the sam e fractures is 13 7 mm; on this

basis, the RQD is 100 per cent. As this is obviously in-

c orre ct, it is e sse ntia l th at th e c ylin de r o f th e c ore s (so un d

cores) should exceed 100 m m in length. A t the quoted 40

degree intersection, the core cylinder would be only

91 mm and the RQD 0 per cent. The length of core used

fo r th e calculatio n is m easu re d fro m fracture to fra cture

along the axis of the core.

In the determ ination of the R QD of rock surfaces, the

sam pling line m ust be likened to a borehole core and the

fo llowin g p oin ts o bse rv ed :

. experience in the determ ination of the RQ D of core

is necessary;

.

do not be m isled by blasting fractures;

. weaker bedding planes do not necessarily break when

cored,

.

assess the opposite w all w here a joint form s the side-

wall,

. shear zones greater than 1 m m ust be classified sepa-

rately.

Joint Spacing JS)

A maximum of a three-joint set is assumed, Le. the

num ber required to define a rock block. W here there are

fou r o r more joint sets, the th ree closest-spaced join ts are

used. The original chart for the determ ination of the JS

rating has been replaced by that proposed by Taylor4.

From the chart in Fig. 2 it is possible to read off the rating

for one-, tw o-, and three-joint sets.

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I 2 3

4 5

Class A B A B A B A

B A

B

Rating

loo-81 80-61 60-41 40-21 20-0

Description

V er y G oo d

Good Fair Poor

V ery P oo r

Colour Blue Green Yellow Brown

Re d

F ra ctu re f re qu en cy , F F/m

Joint

Rating

IR S-M Pa rating

R QD ra tin g

spacing

A ve ra ge p er

07 0 07 0

m metre I set 2 set 3 set

> 185

20 97-loo 15

025

0, 1

40 40 40

165-185

18

84-96

14 See F ig. 2

0,15

40 40

40

145-164

16

71-83

12

0,20

40

40 38

125-144

14

56-70

10

0,25

40

38 36

105-124

12

44-55

8

0,30

38

36

34

85-104 10 31-43 6 0,50 36 34 31

65-84 8 17-30

4

0,80

34

31

28

45-64 6

4-16

2

1,00

31

28

26

35-44 5

0- 3

0

1,50

29

26

24

25-34

4

2,00

26

24

21

12-24 3

3,00

24 21

18

5-11

2

5,00

21 18 15

1-4

I

7,00

18 15 12

10,00

15

12

10

15,00

12 10 7

20,00

10

7 5

30,00

7

5

2

40,00

5 2

0

ALLOW FOR CORE RECOVERY

TABLE I

GEOLOGICAL PARAMETERS AND RATINGS

1. M eaning of the ratings

D istinguish betw een the A and B sub-classes by colouring the A sub-class full and cross-hatch the B .

2 . P aram eters an d ratin gs

T AB LE I continued opposite

T A BLE III

BOREHOLE LOG SHEET

S am plin g p ro ce du re

B oreh ole N o:

Z on in g o f b or eh ole

I nte rv al le ng th A

Total sound core B

B

RQD, 070

- x lOO

A

Lo w

angle

0-29

Date:

TABLE II

FACTORS TO G IVE AVERAGE FRACTURE FREQUENCY

Factor

Joint

spacing

Number

M ean spacing A

True d is tance

=

A x sin 0,26

Number

M ean spacing B

True d is tance

=

B x sin 0,71

Number

M ean spacing C

True d is tance

=

C x sin 0,97

=

Sum of individual FF/m inverse of spacing

2

F in al R atin g

a. One set of three sets on a line, or one set only

b. Two sets of three sets on a line or two sets only

c. All of the sets on a line or borehole core

d. Two sets on one line and one on another

e. T hree sets on three lines at right-angles

1, 0

1, 5

2, 0

2, 4

3, 0

Moderate

angle

30-59

High

angle

60-90

Average f requency

IR S

RQD

Join t s pa cin g

Joi nt cond it ion

Total

Remarks

S in v al ue s

0-29

=

0,26

30-59

=

0,71

Signature:

60-90

=

0,97

260 OCTOBER 1990

JOURNA L OF TH E SOUTH AFRICA N INSTITU TE O F M INING N MET LLURGY


5/17

Accumulative

7

adju stm ent o f p o ssib le ratin g of 40

Adjustment,

7

M o d. p re ss ur e

H ig h p re ss u re

2 5-12 5 > 1 25

Parameter

Description

D ry

M oist U rn U rn

A M ulti w avy directio nal

lO O lO O

95

90

U ni 9 5 9 0

85 8 0

Large-scale

C u rv ed 8 5 80

75 7 0

j oi nt e x pr es si on

S lig h t u nd ula tion 8 0 7 5 70 6 5

Straight

75

70

65

60

B

R o u g h s te p p ed /i rr e gu la r

95

90

85 8 0

S m o oth s tep pe d 9 0

8 5 80

75

S m a ll -s c al e j oi n t

S lic ken side d stepp ed 8 5

8 0 75

70

expression

R o ug h u n du la ti ng

80

7 5 70 6 5

20 0 m m x

S m o ot h u n du la ti ng

7 5 7 0 65 6 0

20 0 m m

S licken sid ed u nd ula ting 7 0 6 5 60

55

R ou gh p la na r

65

6 0 55 5 0

S m o oth p lan ar 6 0

5 5 50

45

P o lishe d 5 5 50 45 4 0

C

]

o in t w all a lte ra tio n w ea ke r th an w all r oc k a nd o nly

if it is w ea ker than th e fillin g

75

70

65 6 0

D

N on -so ften ing C oa rse

90

85

80

75

a nd s he ar ed

Me d i u m

85

80

75 7 0

material

Fine

8 0 7 5 70 6 5

]

o in t f il li ng

S of t s he ar ed

Coarse

7 0 6 5 60

55

m ate ria l, e .g .

Me d i u m

60

5 5 50

45

talc

F in e 5 0

4 5 40 3 5

G o ug e t hi ck n es s

< a m plitu de o f ir re gu la ritie s

4 5 4 0 35 30

G o ug e t hi ck n es s

> a m plitu de o f ir re gu la ritie s

30

2 0 IS 1 0

T AB L E I continued from opposite page)

3 . A ss es sm en t o f jo in t c on ditio n

E x am ple: A straigh t jo in t w ith a sm oo th su rfa ce and m ed ium shea red talc un de r d ry c on ditio n s giv es

A

=

7 0 0 70 , B

=

65 7

D

=

6 0 07 0 ; to ta l a d ju st m en t

=

7 0 x 65 x 6 0

=

27 7

an d th e rating is

40 x

27 7

=

11 .

T h e roc k m ass ratin g R M R) is the sum o f th e ind ivid u al rating s.

fo llo win g situ atio ns a pp ly :

. if all the features are presen t in th e sidew alls, establish

w hether they intersect a ho rizo ntal line;

. if they all do no t intersect the ho rizo ntal line, m easure

on a vertical line as w ell;

. if a set is parallel to the sid ew all, m easure these o n

a lin e in the hang ing at righ t-an gles to the sidew all.

Th is con flicting situation of d ifferen t sam pling p ro-

ced ures can be reso lved if th e su m of the m easu rem ents

is divided b y a factor to arrive at th e averag e frequen cy.

T hese factors are sh ow n in T ab le 11, w h ich can be ap-

p reciated if com pared w ith the sam pling o f the sid es of

a cube o n d ifferen t lin es on intersection.

Th e need for accurate sam pling canno t be too high ly

stressed . O ften detailed scan -line surveys are d one o n

sid ew alls th at d o not intersect all the features, and then

this biased inform atio n is an alysed in detail.

W here bo reho les do n ot intersect all the features at 45

d egrees, a sam pling b ias w ill o ccu r unless p rov ision is

m ade for the an gle o f in tersection, as in the lo g sh eet of

T able Ill.

Th e a verage fracture freq uency per m etre FF Im ) is

used in T able I to determ ine the rating. T he inverse o f

this num ber giv es the average fracture spacing. T he data

fro m A and B can be used only if the joint spacin g for

all the sets is approxim ately the sam e.

F ig . 3 sh ow s th e re la tio nsh ip b etw ee n F F/m a nd ra tin gs

after the d ifferent sam pling techniques for co re and

underground expo su res have been adjusted to an av erage

spacing.

B ec au se th e F F Im in clu de s b oth c on tin uo usG oin ts) a nd

d isc on tin uo us fra ctu re s) fe atu re s, th e c on tin uity m ust b e

estim ated to giv e the joint spacing and rock b lock size

F ig. 4 ). T hu s, the F F/m w ill g ive the rock-m ass rating,

but this has to be ad justed by the factors g iven in T able

IV .

C or e R ec ov er y

A s the FF /m does n ot recognize core recov ery, the

FF /m m ust be increased ifthere is a core loss, w hich w ill

occur in the w eaker sections of the core. T he adjustm ent

is do ne by div idin g th e FF I m by th e co re recovery an d

m ultiplying the quotient by 100.

JO U R N A L O F TH E S O U T H A F R IC A N IN ST IT U T E O F M IN IN G A N D M E T A L L U R G Y

O CT OB ER 19 90

26 1


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7

I

/

[7

/

/

/

V

/

/

/

v

/

/

/

/

V

Rating

J oi nt s pa ci ng

Rating

m

R Q D

J5

Combined

FF/m

0,025

o

I I

1

0,05

o

1, 5

1, 5

5

0,10

8 3 11

10

0,20 12

5

17

15

0,50 14

10 24

20

1,00

15 13 28

26

2,00 15 19 34

31

3,00

15 21

36

33

4,00 15

23 38

36

5,00 15

25 40

38

«J

.J S

~3 0

0

0

a:

.2 S

C)

Z

U

c; t

~

20

I-

~

0

21 5

0

Z

I-

er

a: 10

J

0

60

60

«J 30

20 / J

/0

l

5

40

35

30

25

20

/5

/0

5

3

2

/.0 0.8

5

0

02 0./5

0/

3

A V E R A G E F R A C T U R E F R E Q U E N C Y P E R M E T R E

F F / m

C O R E R E C O VE R Y

Fig. 3-R atings for fracture frequency per m etre

T A B LE IV

F A C TO R S B Y W H I C H J O IN T F R EQ U E N C IE S A R E M U L T IP LI ED

C on tin uou s fea tu re s

07 0

Fact or

10 0

90

80

70

60

50

1, 0

0, 9

0, 8

0, 7

0, 6

0, 5

Comparison of the Two Techniques

T he ad vantage of th e F F / m techn iq ue is that it is m ore

sensitiv e th an th e R QD for a w id e rang e of join t spacin gs,

because the latter m easures o nly core less th an 1 00 m m

an d rap idly chan ges to 1 00 p er cen t. Ex am ples of th is are

sho w n in T ab le V , w hich assum es that there is a percent-

age of core g reater th an 1 00 m m at join t intersection s.

Th e fracture-frequ ency techn iq ue w as first u sed in

C hile in 1 985 an d then in C anada in 1 986 . In Z im babw e,

th e FF /m tech niq ue w as used in con jun ction w ith the

R Q D an d JS tech niq ue an d w as foun d to b e just as

accurate.

Jo int C o nd ition an d W ater

Jo in t cond ition is an assessm ent o f the frictional pro-

perties o f the join ts no t fractures) an d is based on ex-

p re ss io n, s ur fa ce p ro pe rtie s, a lte ra ti on z on es , fil li ng , a nd

w ater. O riginally the effect o f w ater w as catered for in

T A B LE V

C O M P A R IS O N O F T E CH N IQ U E S

a se pa ra te se ctio n: h ow ev er, it w as d ec id ed th at th e a sse ss-

m en t o f joint con ditio n allow in g fo r w ater inflow w ould

h ave g reater sensitivity3 . A total ratin g of 4 0 is no w

a ssig ne d to th is se ctio n. T he p ro ce du re fo r th e d ete rm in a-

tion o f joint con ditio n is sho w n in T ab le I, w hich div ides

th e jo in t-a sse ssm en t se ctio n in to su b-se ctio ns A , B , C , D .

Su b-section A caters for th e la rg e-scale ex pression o f

the feature, su ch as acro ss a drift or in a pit face. B

a ss es se s th e s m all- sc ale e xp re ss io n a nd is b as ed o n t he p ro -

file s sh ow n in Fig. 5. S ection C is app lied o nly w hen there

is a distin ct d ifference betw een the hardness of the host

rock and that of th e joint w all. S ection D cov ers th e va ria -

tion s in jo in t filling .

A s th e cond ition s o f the different jo int sets are not

26 2

O CTO BER 1990 JO U R N A L O F T H E S O U TH A F R IC A N IN S TIT U T E O F M IN IN G A N D M E T A L L U R G Y


7/17

\

\

~ \

\

I

~I \.

1 -.

I

\

I

I

\

,

JOINT SPACINGCm)

o,F

0,.

Of

°r

0,5

1,0

I I

BLOCK SIZE

,~ )

. 0 , 0 01

q0 8

al2

1,0

I I I

I

ISOLAT1 ::D DRAW

6m

ZONE D IAMETER

I

Bm

A B C

4O p

a w

op

~

.....

S

5,0

Z

.....

Z

0

0:::

0

lJ...

0

W 1,0

Cl )

::>

J

0


8/17

Potential w eathering and adjustm ents.

D egree of

weathering

Y2y

I

y

2y

3y

4

y

Fresh

10 0

100 100

100 100

Slight

88 90 92

94

96

Moderate 82 84 86

88 90

High

70 72

74

76 78

Complete

54 56

58

60 62

Residual soil 30 32

34

36 38

I

-

--

.......

ROUGH STEPPED / IRREGULAR

][

--...

SM OOTH STEPPED

m

PERCENT

ADJUSTMENT

95

90

SLlC KEN SID ED STEPPED

85

N:

-

ROUGH / IRREGULAR UNDULATING

x.

-

SM OO TH U ND ULA TING

3Z I

........

80

-

--

F ig . 5 -J oin t ro ug hn es s

profiles

75

SLlC KEN SID ED U ND ULA TIN G

7.0

1ZII

ROU GH / IRREGU LA R PLA NA R

65

SMOOTH PLANAR

60

IX

PO LISH ED PLANAR

55

tion and the rate of m ining.

T he three param eters that are affected by w eathering

are the IRS, RQD or FF fm , and joint condition. The

RQD percen tag e can be d ecre ased by an in crease in frac -

tures. The IRS can decrease significantly as chem ical

changes take place; in fact, there is the situation with

kim berlites, where solid hard rock becomes sand in a

sh ort tim e. T he jo int co nd ition is affec ted b y alteration

of the wallrock and the joint filling. W eathering data

based on the exam ination of borehole cores can be con-

se rv ative owing to the large surfa ce area o f c ore relative

to th e volum e-un derg ro un d ex po sures are more reliable.

T able V I show s the adjustm ent percentages related to

degree of w eathering after a period of exposure of half,

one, two, three, and four-plus years.

26 4

TABLE VI

ADJUSTMENTS FOR WEATHERING

J oin t O rie nta tio n

The size, shape, and orientation of an excavation af-

OCTOBER 1990

JOURNAL OF THE SOUTH AFRICAN INSTITUTE OF MINING AND METALLURGY


9/17

No. of joints

No. of faces inclined away from the vertical

defining the

block

701170

751170

801170 851170

901170

3

3

2

4

4 3

2

5

5

4

3

2 I

6

6 5

4 3

2,1

Adjust- Adjust- Adjust-

Average Plunge

ment

Plunge

ment

Plunge

ment

rating

degree

1170

degree

1170

degree

1170

0- 5

10-30

85

30-40

75

>4 0

70

5-10 10-20 90 20-40 80 >4 0 70

10-15 20-30

90

30-50

80

>50

75

15-20 30-40

90

40-60 85

>60

80

20-30 30-50

90

>5 0

85

30-40 40-60

90

>5 0

90

fects the behaviour of the rock m ass. T he attitude of the

joints, and whether or not the bases of blocks are ex-

posed, have a significant bearing on the stability of the

excavation, and the ratings m ust be adju sted according-

ly. The magnitude of the adjustment depends on the

attitude of the joints w ith respect to the vertical axis of

the block. A s gravity is the m ost significant force to be

considered, the instability of the block depends on the

num ber of joints that dip away from the vertical axis.

The required adjustm ents are show n in Table V II.

T ABLE VII

PE RCE NT AG E A DJU STM EN TS F OR JO IN T O RIE NT ATIO N

T he orientation of joints has a bearing o n the stability

of open stopes and the cavability of undercut rock

masses.

T he a dju stm en ts fo r th e o rie ntatio n o f sh ea r z on es w ith

respect to development are as follows: 0-15° =

7611/0,

15-45° = 84 ,45-75° =

92 .

Advance of the ends in the direction of dip of struc-

tu ra l fe atu re s is p re fe ra ble to d ev elo pment a ga in st th e d ip .

A n adjustm ent of 90 per cent should be m ade to previous

adjustm ents w hen the advance is against the dip of a set

o f closely spaced joints. T his is because it is easier to sup -

port rock blocks that have the prom inent joints dipping

w ith the adv an ce.

The adjustm ent for shear-zone orientation does not

apply to jointed rock . T he m axim um rating is therefore

joint orientation m ultiplied by direction of advance,

w hich is 70 x 90

=

63 .

T he e ffe ct o f jo in t o rie nta tio n a nd co nd itio n o n stab ili-

ty is clearly displayed in bridge arches m ade from high-

fric tio n ro ck b lo ck s.

Joint-orientatio n A djustm ent for P illars and S idew aU s

A mod ifie d o rie nta tio n a dju stm en t a pp lies to th e d es ig n

o f p illa rs o r s to pe sid ew alls . A dju stm en ts a re m ad e whe re

joints define an unstable w edge w ith its base on the side-

w all. The instability is determ ined by the plunge of the

in te rs ec tio n o f th e lower jo in ts, a s w ell a s b y th e c on ditio n

of the joints that define the sides of the wedge (Table

VIII).

Min ing- induced S tr es se s

M inin g- in du ced s tr es se s r esult f rom th e r ed is trib ut io n

o f fie ld (re gio na l) s tre sse s th at is c au se d b y th e g eome try

and orientation of the excavations. The m agnitude and

ra tio o f th e fie ld s tre sse s s ho uld b e k nown . T he re dis trib u-

tion of the stresses can be obtained from m odelling or

from p ublished stress-redistribution diagram s7.8. T he

redistributed stresses that are of interest are m axim um ,

m in imum , a nd d iffe ren ce s.

T A BLE VIII

PERCENTAGE ADJUSTM ENTS FOR THE PLUNGE OF THE

INTERSECTION OF JOINTS ON THE BASE OF BLOCKS

M axim um Stress

The max imum p rin cip al stre ss c an c au se s pa llin g o f th e

w all p aralle l to its o rie nta tio n, th e c ru sh in g o f p illa rs , an d

th e d efo rm atio n a nd p la stic flow o f s oft zo ne s. T he d efo r-

m ation of soft intercalates leads to the failure of hard

z on es a t re la tiv ely low stre ss le ve ls . A c ompre ss iv e stre ss

at a large angle to joints increases the stability of th e rock

m ass and inhibits caving . In this case, the adjustm ent can

be up to 120 per cent, Le.. im proving the strength of the

rock m ass.

M inim um Stress

T he m in im um principal stress plays a significant role

in the stabilities of the sides and back of large excava-

tio ns, the sides of stapes, and the m ajor an d m inor apexes

that protect extraction horizons. T he rem oval of a high

horizontal stress on a large stope sidew all w ill result in

relaxation of the ground tow ards the opening.

Stress Di fferences

A large difference betw een m axim um and m inim um

stresses has a significant effect on jointed rock m asses,

re su ltin g in s he arin g a lo ng th e jo in ts . T he e ffe ct in cre as es

as the joint density increases (since m ore joints w ill be

u nf av ou ra bly o rie nta te d) a nd a ls o a s th e jo in t-c onditio n

ratings decrease. The adjustm ent can be as low as 60 per

cent.

Fac to rs in th e A ss es smen t o f M in ing i nduc ed S tre ss

T he follow ing factors should be considered in the

assessment of mining-induced stresses:

. d rift-in du ce d s tre sse s;

. in teractio n o f clo se ly sp ace d d rifts;

. location of drifts or tunnels close to large stopes;

. abutm ent stresses, particularly w ith respect to the

direction of advance and orientation of the field

stresses (an undercut advancing tow ards m axim um

s tre ss e nsu re s g oo d c av in g b ut c re ate s h ig h a bu tm en t

s tr es se s, a nd

v ic e v er sa ;

. uplift;

. point loads from caved ground caused by poor frag-

mentation;

. rem oval of restraint to sidew alls and apexes;

. in cre ase s in s iz e o f m in in g a re a ca us in g c ha ng es in th e

geometry;

. m assiv e w ed ge failu res;

.

influence of m ajor structures not exposed in the ex-

cavation but creating the probability of high toe

stresses or failures in the back of the stope;

JOURNA L O F THE SOUTH A FR IC AN IN ST ITU TE O F M IN ING AND META LLURGY

OCTOBER 99 265


10/17

. presence of intrusives that m ay retain high stress or

shed stress into surrounding, m ore com petent rock.

The total adjustment is from 60 to 120 per cent. To

arrive at the adjustm ent percentage, one m ust assess the

effect of the stresses on the basic param eters and use the

total.

B last ing Ef fec ts

B lasting creates new fractures and loosens the rock

m ass, cau sing movem en t o n jo in ts, so tha t th e follow ing

adjustm en ts sho uld b e app lied :

Technique

Boring

Smoo th -wa ll b la sti ng

Good c on ve ntio na l b la stin g

Poo r b la st in g

Adjustment,

10 0

97

94

80 .

The 100 p er cent adjustm ent for boring is based on no

dam age to the w alls; however, recent experience with

ro adh eader tun nellin g show s th at stre ss deterioratio n

occu rs a short distance from the fac e. T his ph eno men on

is being investigated since good blasting m ay create a

b et te r wal l condit io n.

It should be noted that poor blasting has its greatest

effect on narrow pillars and closely spaced drifts ow ing

to the lim ited amount of unaffected rock.

Su mmary o f A dju stm ents

A djustm en ts must reco gn ize th e life o f the ex cava tio n

and the tim e-dependent behaviour of the rock m ass:

Parameter Possible adjustment,

Weathering 30-100

Orientation 63-100

Induced stresses 60-120

Blasting 80-100.

A lthough the per centage s a re empi ri ca l, t he adju stment

principle has proved sound and, as such, it forces the

designer to allow for these im portant factors.

STRENGTH OF THE ROCK MASS

The rock -m ass streng th (R M S) is d erived from th e IR S

and the RM R5. The strength of the rock m ass cannot be

higher than the corrected average IRS of that zone. The

IRS has been obtained from the testing of small speci-

m ens, but testw ork done on large specim ens show s that

their strengths are 80 per cent of those of small speci-

m ens4. As the rock m ass is a 'large' specimen, the IRS

must be reduced to 80 per cent of its value. Thus, the

strength of the rock m ass would be IRS x 800/0 if it had

no joints T he effect of the joints and its frictional pro-

perties is to reduce the strength of the rock m ass.

T he follow ing procedu re is ado pted in th e calcula tio n

of RM S:

. the IRS rating(B) is subtracted from the total

rating (A ) and, therefo re, the balan ce, L e. R QD , joint

spacing, and condition are a function of the rem ain-

ing possible rating of 80;

. the IRS(C) is reduced to 80 per cent of its value,

RMS

=

A -B

C

80

80

x x

100'

26 6

OCTOBER 1990


e.g. if the total rating w as 60 with an IRS of 100 M Pa

and a rating of 10, then

RMS = 100MPa x

(60

- 10)

x

80

50MPa .

80 100

=

D ESIG N S TR EN GT H O F T HE R OC K M ASS

The desig n roc k-m ass streng th (D RM S) is the stren gth

of th e u nco nfined ro ck m ass in a sp ecific m in ing e nviro n-

m ent. A m ining operation exposes the rock surface, and

th e c on ce rn is w ith th e sta bility o f th e z on e th at su rro un ds

the excavation. The extent of this zone depends on the

size of the excavation and, except w ith m ass failure, in-

stability propagates from the rock surface. The size of

the rock block will generally define the first zone of in-

stability. Adjustm ents, w hich relate to that m ining en-

vironment, are applied to the RMS to give the DRMS.

As the DRM S is in m egapascals, it can be related to the

min ing- induced s tr es se s. The re fo re , t he adju stment s u sed

are those for w eathering, orientation, and blasting. For

exam ple, if

weathering

=

85 , orientation =

75 , blasting =

90070,total =

57 , and RMS =

50 , the adjus tmen t

=

57 and the DRMS = 50 x 57 = 29 M Pa.

T herefore , th e rock m ass ha s an un con fin ed co mpressive

strength of .29 MPa, which can be related to the total

stresses.

PRESENTA TION OF DA TA

The rating data for the rock mass should be plotted

on plans and sections as class or sub-class zones. If the

A and B sub-divisions are used, the A zones can be

coloured full and the B cross-hatched. These plans and

sections now provide the basic data for m ine design. T he

layouts are plotted w ith the adjusted ratings (M RM R),

which w ill highlight potential problem areas or, if the

layout has been agreed, the support requirem ents w ill be

based on the M RM R or DRM S. In the case of the DRM S,

the values can be contoured.

P ract ical Appl ica tions

The rock mass can now be described in ratings or in

m egapascals; in other words, these num bers define the

strength of the m aterial in which the m ining operation

is go ing to take place. E xc avation stability o r instab ility

has been related to these num bers. O n the m ines in w hich

the system has been in operation, its introduction was

welcom ed by all departm ents from those dealing with

g eolo gy to th ose invo lve d in p ro du ctio n.

W ithin the scope of this paper, the practical applica-

tions are described in broad term s to ind icate th e b enefits

achieved from the use of this system.

Communication

C ommun ication betw een variou s d epartm ents has im -

p ro ve d sin ce th e in tro du ctio n o f th e c la ssific atio n sy stem

because num bers are used instead of vague descriptive

terms. It is well known that the term inology used to

d esc rib e a p artic ula r ro ck mass b y p erso nn el e xp erie nc ed

in the m ining of good ground is not the sam e as that used

by personnel experienced in the m ining of poor ground.


11/17

a a

b b a a

b b

b b b c

c c c d d

d e f f

c+ l

flp h + flp

h+fll h+fll

h + flp

flp

Suppo rt P rin cip le s

T he R M R is taken into con sid era tio n in d esig ning su p-

p ort ev en tho ugh th e ad ju sted rating s M R MR are used .

The reason is that a class 3A adjusted to SA has rein-

forcem ent p ote ntial, w hereas an

in s itu

class SA has no

reinforcing po ten ti al .

Su pp ort is req uired to m ainta in th e integrity of the ro ck

mass and to increase the DRMS so that the rock mass

can support itself in the given stress environm ent. The

installation must be timed so that the rock mass is not

allow ed to fail and should therefore be early rather than

late. A support system should be designed and agreed

b efo re th e d eve lop ment stag e so tha t th ere is inte ractio n

b etw ee n th e c omponents o f th e in itia l a nd th e fin al sta ge s.

To control deform ation and to preserve the integrity of

the ro ck m ass, the in itial sup port sh ou ld b e installed con -

currently w ith the advance. T he final support caters for

t he min ing- induced s tr es se s.

A n inte grated su pp ort system con sists o f compo ne nts

th at a re in te ra ctiv e, a nd th e su cc ess o f th e sy stem d ep en ds

o n th e c orre ct in sta lla tio n a nd th e u se o f th e rig ht mate ria l.

E xperience has show n that sim ple system s correctly in-

sta lle d a re more sa tisfa cto ry th an c omplic ate d te ch niq ue s

in w hich the cha nces of erro r a re high er. T he sup erv iso ry

staff m ust understand and contribute to the design, and

th e d esig n sta ff must re co gn iz e th e c ap ab ilitie s o f th e c on -

s tr uc tio n c rews and any logi stic al p roblems. The con st ru c-

tion crew s should have an understanding of the support

p rinciples and th e co nseq uen ces of po or installatio n.

Layout of Support Guide for Tunnels Using MRMR

T able IX show s how the support techniques, in alpha-

betical symbols, increase in support pressure as the

MRMR decreases. Both the RMR and the MRMR are

sh own a s su b-c la sse s.

TAB LE IX

SUPPORT- PRESSURE FOR DECREASING M RM R

RM R

lA lB 2A 2B 3A 3B 5AA 4B

- Roc k r ein fo rc emen t-p la stic d efo rma tio n- +

lA

lB

2A

2B

3A

3B

4A

4B

5A

5B

*

The codes for the various support techniques are given in Table X.

A djusted ratings m ust be used in the determ ination of

su pp ort re qu irements. In sp ec ia liz ed c ase s, su ch a s d raw-

p oin t tu nn els, th e a ttritio n e ffe cts o f th e d rawn c av ed ro ck

and sec ond ary blasting must b e reco gn ized , in w hich case

the tunnel support shown in Table IX would be sup-

plem ented by a m assive lining.

T he sup po rt tech niqu es sho wn in T able X are examples

o f a prog ressive in crease in su pp ort p ressu res and a re no t

a c omplete spectru m o f tech niq ues. Where w eatherin g is

likely to be a problem, the rock should be sealed on

exposure.

T ABLE X

SUPPORT TECHNIQUES

Ro ck r ei nf or ce m en t

a Local bolting at joint intersections

b Bolts at I m spacing

c b and straps and mesh if rock is finely jointed

d b and m esh/steel-fibre reinforced shotcrete bolts as lateral

restraint

d and straps in contact w ith or shotcreted in

e and cable bolts as reinforcing and lateral restraint

f and pinning

Spilling

Grouting

e

f

g

h

Rig id l in in g

j

Timber

]

k Rigid steel sets

L d f f

I M assive concrete

ow e orma IOn

m k and concrete

n Structurally reinforced concrete

Yielding l in ing repa ir t echnique i deformation

0 Yielding steel arches

p

Yielding steel arches set in concrete or shotcrete

ill

q

Fill

S pa llin g c on tr ol

r Bolts and rope-laced mesh

R oc k r ep la ce me nt

s Rock replaced by stronger material

Developm ent avoided if possible

5B

Layout of Support Guide Using the DRM S

T he support guide for tunnels using the D RM S and the

support techniques of Table IX are shown in Figs. 6

and 7.

S tabil ity and Cavabil ity

The relationship between the ratings adjusted for

stability or instability M RM R and the size of excava-

tion is show n in Fig. 8. The exam ples of different situa-

tion s w ere tak en from op erations at the fo llow in g m in es:

. Freda, Oaths, King, Renco, and Shabanie M ines in

Zimbabwe

. Andina, Mantos Blancos, and Salvador M ines in

Chile

. Bell and Fox M ines in Canada

.

Henderson M ine in the USA.

T he d iag ram re fers to the stab ility o f th e rock a rch , w hich

is depicted in three em pirical zones:

. a stable zone requiring support only for key blocks

or brows, i.e. skin effects

.

a tr an si tio n zone requ iri ng s ub stanti al p en etr ativ e s up -

port and/or pillars, or provision to be m ade for dilu-

tion owing to failure of the intradosal zone,

OCTOBER 99 267O URN AL O F TH E SO UTH AFRIC AN IN STITUTE O F M ININ G AN D M ETALLUR GY


12/17

INCREASING

,

/

PLA~

T IC DEFORM

JlON /

/ k

/

/

/

INCREASINI

ROCK RE IN

ORCINGPOT

NTlAL

~/

c /

/1

I

-

/

/

/ /

/

/

/ 11

/

/

I

./,

/

~-

/

m

/

,/

b

/

. + 0 /

,/

/k

/

/

/

/

/

.

./

/

d

/

/

/

/

.. 0

/

/

,

/

e

/

/

./

//

/

1/

,/

a

/(

/

/

h

/,

]I

/

/

/

/

J

/ /

d

1,..-/

/

/

/

/

,

/

e

/

f + 0

/

/

/

/

/

f

/

/

/

I/

a

/

/

/

/

m

/

/

b

/

/

,

/

/

/

,

+ 0

V

d

/

/

,

/

/

/

/

.

/

/

/

/

/

/

,

1V

. I

/

,

/ /

1 < S TA BLE

/

/

/

q/

iI

I

/

IT =

SUPPORTKEY BLOCKS

-

/

/

/

/

Y.

ill =

SUPPORTEFFECTIVE

/

/

,.I

/

N=FAI LURE CONTROLLED

-

/

/

~=COLLAPSEICAVING

J

/

/

.

/

/

3

r< )

b

I

b

4

0

a.

~Cl)

Cl )

W

0:::

f-

Cl )

f-

Z

W

6

~Z

0

0:::

>

Z

W

(9

Z

Z

8

7

4

DESIGN ROCK MASS STRENGTH MPo

5

1

eo

5

7

8

9

2

. a caving or subsidence zone in w hich caving is pro-

pagated provided space is available or subsidence

orcurs.

T he size o f the excavation is defined by the hydrau lic

radius or stability index, w hich is the plan area divided

by the perim eter. O nly the plan area is used for excava-

tions w here the dip of the stope or cave back is less than

45 degrees. W here the dip is greater than 45 degrees, the

area and orientatio n of the b ack w ith respect to the m ajor

stress direction m ust be assessed.

For the sam e area, the stability index (SI) will vary

dependin g on the relationship betw een the m axim um and

the m inimum spans. For example, 50 m X 50 m has the

same area as 500 m x 5 m, but the SI of the first is 12,5

268

O CTO BER 1990


3

2

F ig . 6 --Suppor t r equ ir ements

fo r m ax imum st re ss

w hereas the SI -of the second is only 2,5. The large 50 m

X 50 m stope is less stable than a 500 m X 5 m tunnel,

and this is well illustrated by the difference in the SI.

I nd es tru ctib le p illa rs (r eg io na l) r ed uc e th e spans so th at

the SI is applied to individual stopes. Sm all pillars, as

in a post-pillar operation, apply a restraint to the hang-

ingw all, w hich results in a positive adjustm ent and, as

su ch , a h ig her ratin g, s o th at th e o ve ra ll sto pe d im en sio ns

c an b e in cre as ed w ith in th e d ic ta te s o f re gio nal sta bility .

In a room -and-pillar m ine, the pillars are designed to

ensure r eg io na l s ta bi lity .

The stability or cavability of a rock m ass is determ in-

ed by the extent and orientation of the w eaker zones.

There is a distinction betw een m assive and bedded


13/17

,,

;.~

/'

k

./

C

,'

,,

./

'

,, k

./

.

b

/'

....

,,

/

g

,,/'

....

/

r

.

d

m/,

,,-r

.

/

/'

d

/'

,...../

a

/'

.

./

/'

[

.

+

0

~,....

,,

'

/'

/

/'

f

,,'

./'

/'

/'

./

b

/'

/'

h

/'

. 0

/

/

/

,,'

/'

/

/'

./

nr

/'

/

./

b

/'

.I

/ /' /

./

d

/

'

1.../

0/

.

/

/

N

/

f

/;

,.

/'

/'

/'

,

'

V.

/'

/

/

/'

1- STA BLE

II =

SU PPO RT I

Z

W

( )

~

z

~

6

7

8

9

I O

/2

de posits in that the bed ding cou ld be a do minan t featu re.

Stability of O pen Stopes

L arge, open stopes are generally m ined in com petent

ground, the size of the stope being related to the criteria

for regional stability (Fig. 8). T he stability of the stope

hangingwall has to be assessed in term s of whether the

personnel are to work in the stope or not.

If personnel are to work in the stope, the back must

be stable im mediately after m ining. In order to achieve

th is sta bility , p ote ntia l ro ck fa lls n ee d to b e id en tifie d a nd

dealt w ith. If the environm ent and m ining rate perm it it,

or if skilled personnel are available, the support can be

designed for the local situation. H ow ever, if the m ining

D E S IG N R O K M S S S T R E N G T H

MPa

6

5

4

3

rate is high, or the identification of potential falls is dif-

ficu lt, a blanke t-su ppo rt design is req uired .

In the case of open stopes where the activity is from

su b-levels o utside th e stop e, the local instability affe cts

the am ount of dilution before a stable arch has form ed.

In the worst situation, the intradosal zone can have a

height that is 25 per cent of the span.

B y u se of a combination of join t-con dition ra tin gs an d

jo in t- or ienta tio n dat a, a condi ti on /o rient ati on perc en tage

c an b e d erived. T hese percentages are sh ow n in T ab le X I.

T hese percentages can be used to define areas requir-

ing support as follow s:

600/0- 70% Highly unstable, collapse with blast,

r equi res p resupport

JOURNA L O F THE SOU TH A FR IC AN IN STIT UT E O F M IN ING AND MET ALLURGY

OCTOBER 9 9

26 9


14/17

~=--~

8

STABLE

(L OC AL S UP PO RT )

7

en


15/17

Dip fr om v ertic al.

D ip towa rd s v er tic al.

Condition

rating

0-40°

40-60° 60-80°

80-90° 90-80° 80-60° 60-40°

40-0°

0-10

60

65

70

75 75 80

90 90

11-15

65 70 75

80 80

85

90

10 0

16-20 70 75 80 85 90 95 100

21-25

75

80

85 90

95

100

26-30

80 85

90

95

lOO

31-40

85 90

95 100

MRMRI

MRMR2 MRMR3 MRMR4

MRMR5

1. C ave A ngle

D epth, m Unres Res Unres Res Unres Res Unres Res Unres Res

lOO

70-90 85-95 60-70 75-85 50-60 65-75 40-50 55-65 30-40 45-55

50 0

70-80 80-90

60-70 70-80 50-60 60-70

40-50

50-60 30-40

~ ()-50

2. Extent of

ilure Zone

D epth, m

Surf.

U /G

Surf VlG Surf

VlG Surf

U/G

Surf VlG

lOO IOm

IOm

20m 20m 30m

30m 50m 50 m 75 m

lOOm

500 IOm

20m

20m

30m

30m

50m

50 m

lOOm

75 m 200m

TABLE XI

PERCENTAGE ADJUSTMENTSFOR DEGREE OF DIP

.Angl es f rom hor iz on ta l.

TABLE XII

THE ANGLE OF CAVE AND THE FAILURE ZONE

Unres

=

No l at er al r es tr ai nt

Re s

=

L ate ra l re str ain t

CONCLUSIONS

The R M R/M R MR classification system h as b een in u se

since 1974, during w hich period it has been refined and

applied as a planning tool to num erous m ining opera-

tions.

It is a com prehensive and versatile system that has

w idesp rea d a cceptance by m inin g p erson nel.

The need for accurate sam pling cannot be too highly

stressed.

T here is room fo r further im pro vem ents by th e ap plica-

tion of practical experience to the em pirical taL les and

charts.

The DRM S system has not had the same exposure but

has proved to be a useful back-up tool in difficult plan-

n ing situation s, a nd has been u sed successfully in m athe-

matica l model ling .

The adjustment concept is very important in that it

fo rc es th e e ng in ee r to re co gn iz e th e p ro blems a sso cia te d

w ith the environm ent with w hich he is dealing.

ACKNOWLEDGEMENTS

T he contributions of H .W . T aylor, T .G . H eslop, A .D .

Surf

=

At sur face

U/G

=

Underground

Wilson, N.W . Bell, T. Carew, and A. Guest to the

d evelopment and app li ca ti on o f th is c la ss if ic at io n sy stem

are acknowledged .

R F R N S

1. B IF NIi\ W SK I, L T . Engineering classification of jointed rock m asses.

Trans. S. Afr. Instn Civ. Engrs vo\. 15. 1973.

2. Li\lIBSCHER, D .H. Class distinction in rock masses. Coal Gold

B ase M in era ls

S.

Afr.

vo\. 23. Aug. 1975.

3. Li\lIBSCHER, D .H . Geomechanics classification of jointed rock

m asse s-m in ing ap plic ation s. Trans. Instn Min. Metall. Sect. Aj

vol. 86. 1977.

4. Ti\YLOR, H .W . A geomechanics classification applied to m ining

problems in the Shabanie and King m ines, Zimbabwe. M .Phi .

Thesis, Univ. of Rhodesia, Apr. 1980.

5. Li\IJBSCHER, D .H . Design aspects and effectiveness of support

system s in different m ining conditions. Trans. Instn M in. M etall.

S ect. Aj vo\. 93. Apr. 1984.

6 . E NG IN EE RS IN TE RN i\T IO Ni\L (N e. C av in g m in e ro ck m ass cla ssific a-

tion and support estimation-a manua\. U .S. Bureau of M ines, con-

tract J0100103, Jan. 1984.

7. HOEK, E., and BROW N, E.T. Underground excavations in rock.

London, Institution of M ining and Metallurgy, 1980.

8. STi\CEY, T.R ., and Pi\GE, CH.

Practical handbook for under-

ground rock m echanics. Trans Tech Publications, 1986.

JO UR N L O F TH E SO UTH FRIC N INSTITU TE O F M INING N D M ET LLU RG Y

OCTO ER

99

27


16/17

Class

5

4 3 2

I

rating

0-20

21-40

41-60

61-80

80-100

B lo ck C avin g

U nd ercut S I m

1- 8

8-18 18-32 32-50

50

Cavability

V er y g oo d

Good

Fair

Poor

V ery p oo r

Fragmentation m 0 01--0 3

0 1-2 0

0 4-5 1 5-9

3-20

2nd l ay -on b la st /d ri ll g /t

0-50

50-150 150-400 400-700 700

0-20

20-60 60-150 150-250

2 50

H angups as

o f to nn ag e

0

15 30 45

>60

D ia. of draw zone m

6- 7

8- 9

10-11 5 12-13 5 15

D rawp oin t s pa n m

Grizzly

5- 7

7-10 9-12

Slusher

5- 7

7-10

9-12

LHD m

9

9-13 11-15 13-18

B row sup po rt Steel and concrete Concrete Blast

Re in f. conc re te

protection

D r if t s uppor t

L ining rock re inf .

Lining

Roc k r ein f.

r epa ir t echn iques

reinf.

W id th of po in t m

1 5-2 4

I

2 4-3 5 2 4-4

4

Direction of advance Towards Iow stress Towards high stress

Comments Fine frag-

Medium Medium Coarse frag-

mentation fragmenta-

c oa rs e f ra g-

mentation

poor g round

tio n go od m entatio n

la rg e LHD s

h ea vy s up -

ground fair

g oo d d rill

d r il l hangups

port repairs

support hangups

S ub le ve l C av in g

Loss of holes Excessive Fair Negligible Nil Nil

B ro w w ear

Excessive

Fair

Low Nil Nil

Support

Heavy

Medium Low Localized Nil

Dilution

Very high H igh

Medium Low

V er y Iow

C ave SI m

1- 8

8-18 18-32

32-50 50

Comments Not practic-

Applicable

Suitable

Suitable

Suitable

able

la rg e HW

c av e a re a

S ub level O pen S to pin g

Min im um s pa n m

1-5 5-20

20-30

30-80

10 0

Stable area Le. SI m N/A

1- 8

8-16

16-35

3 5

TABLE XIII

M INING M ETHOD RELATED TO M RMR

N/A

=

No t avai lab le

TABLE XIV

APPROXIM ATE ANGLES OF PIT SLOPES

Adju ste d c la ss

2

3

4

5

S lo pe a ng le

75

65 55

45 35

27 2

OCTOBER 199

JOURN L O F THE SOU TH FR I N IN STITU TE O F M IN ING ND MET LLURGY


17/17

IR S

0-20

RQD

0-15

JS

0-25

or

FF/m

0-40

JC

0-40

Major

structures.

TABLE XV

OVERVIEWOF THE MRMR SYSTEM

Weathering

3 1 7

r

Orientation

63-100

I

0

RMS

100

RMR

I

Presentation

I. .

CommunIcatIOn

I.

Basic

design

Induced s tr es ses

60-120

I

djUstment

~

DRMS

30-120

MRMR

I

D etaile d d es ig n:

support stability cavability sequence

dri ft o ri en ta ti on a re a o f i nf luence pil la rs

ex cav atio n g eometry in itial d esig n o f p it

slopes

Blasting

80-100

I

Technology development

Innovation in South frican equipm ent

T he synergy of South A frican research and m anufac-

tu rin g h as re su lte d in se ve ra l h ig hly in no va tiv e meta llu r-

g ica l dev ice s in recen t y ears.

C arb on -c on ce ntra tio n Mete r

The latest of these the ultrasound-based carbon-

concentration m eter was developed by M intek w ith

o riginal spo nso rsh ip by the C hamber of M ine s R esearch

Organization and is now being m anufactured and

m arke ted w orldwide b y D ebex E lectron ics in Joh ann es-

burg.

D esigned to achieve precise on-line m easurem ent of

critical carbon-concentration levels during the gold-

reco very pro cess th e no vel instrument m akes po ssible

s ignif ic an t imp rovemen ts and cos t s av ings in me ta ll ur gi ca l

gold-recov ery plants an d h as ex cited inte rn ationa l in-

terest as a new and valuable m etallurgical tool.

D uring the carbon-in-pulp gold-recovery process

carbon granules are added to the gold slurry w hich

follows the initial cyanide-leaching stage. The gold-

cyanide com plex w ithin the slurry is deposited onto the

carb on granu les and th e carbo n-co ncen tration lev el is

th ere fo re c ritic ally importa nt fo r o ptimum gold re co ve ry .

B efo re th e de velopm en t o f the new in strum en t th ere

w as n o w ay of con tinu ou sly and ac curate ly assessin g this

lev el throu gh th e six to e igh t abso rp tion stage s in vo lv ed

since ca rb on -in-pu lp is p umped from on e tan k to a nother

in counter flow to the flow of pulp or slurry.

G iinte r Sommer th e D irector of th e M easu rem en t and

Con tr ol D iv is ion a t M int ek says th at th e car bon- concen -

tratio n m eter is an in ternatio nal first and w as de velope d

.

Released by Group Public Affairs De Beers Industrial Diamonds

p.~. Box 916 Johannesburg 2000.

The D ebm eter system . O n the left cutaw ay view s of the de-

a era to r ta nk a nd u ltra son ic tra nsd uce r arra y system. T he slurry

presentation system is on the right of the draw ing

JOURNA L O F TH E SOU TH A FR IC AN IN STIT UT E O F M IN ING AND META LLURGY

OCTOBER 9 9

27 3

Geomechanics Class System Laubscher Jul 2009

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