Part 09 - Classification of Rock Mass

8/10/2019 Part 09 - Classification of Rock Mass

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PART 9: CLASSIFICATION OF ROCK MASS - RQD, RMR & Q-SYSTEM Soils are classifed according to types & properties e.g. granular soil (-soil) & clay (c-soil).

Rocks are also classifed based on properties. This is to help in understanding theircharacteristics as construction materials & components o engineering structures thus,helping in design & construction ork.

!lassifcation o rocks based on geological aspects are sub"ecti#e$a) %gneousb) Sediment

c) etamorphic 'or design & construction, ob"ecti#e classifcation (numerical #alues) is more appropriate

classifcation o rock based on pre#ailing eakness planes, number o "oint set, &engineering properties like strength, eathering grade & permeability.

A) ROCK QUALITY DESIGNATION RQD: The most basic engineering classifcation introduced by eere (*+), is an inde o

assessing rock /uality /uantitati#ely.

%t is more sensiti#e inde o the core /uality than the core reco#ery$

(Leng! "# $"%eLeng! "# $"%e '%%e)

*++ )

The R0 is a modifed per cent core reco#ery hich incorporates only sound pieces o rock

core that are *11 mm or greater in length along core ais.RQD (./0 " eng! "# $"%e, L) 1 *++

2here$ 3i 4 !ore length *11 mm5 4 5ength o core reco#ered (*.6m i barrel is ull)

C"%e 234e2 "'0ne5 #%"3 %"$6 5%00ng 72!'"%0ng 3$!0ne Y8M


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72! '"%0ng 3$!0ne Y8M

ouble tube core barrel is used to obtain rock core samples during ash boring. 5ength o

barrel is *611 mm.

% core barrel is ull ith rock sample (*11 7 reco#ery, R) then, the total length o core is

*611 mm.

ouble tube core barrel to obtain rock core samples during ash boring.

Triple tube core barrel ensures minimal disturbance to the core sample.

Me!"5 O# O'0n0ng RQD(*)D0%e$ Me!"5:

!ore samples o in-situ rock mass$ %SR recommends a core si8e o at least 93 si8e (6.:mm dia.) drilled ith double-tube core barrel using diamond coring bit.

;rtifcial (not natural) ractures or "oints (that occurs during drilling) can be identifed by

close ftting (matched "oint surace) o cores and resh (unstained) suraces. ;ll the artifcial "oints are ignored hile counting the core length or R0.

; sloer drilling rate ill also gi#e a better R0.


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S N" R"$6 M22 Q;0< RQD ()

* oor =6 61? 'air 61 :6 @ood :6 +16 Acellent +1 *11

C"%%e0"n 'e=een RQD n5 R"$6 M22 Q;0;e2

B!S (>a)

*11

C *=

SD> (>a)=6 * ? 6*1 1.= * =

R0 (7) =6 :1 +1'racture spacing(mm)

1 =11 11

S#e 'e%0ng 4%e22;%e '2e5 "n %"$6 2%eng! & #%$;%0ng


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E134e "# RQD $$;0"n

R0 is perhaps the most commonly used method or characterising the degree o

"ointing in borehole cores, although this parameter also may implicitly include other rockmass eatures like eathering and Ecore lossF.

() In50%e$ Me!"5:

Seismic >roperties G Rock$o The seismic sur#ey method makes use o the #ariations o elastic properties o the rock

strata that aHect the #elocity o the seismic a#es tra#elling through them, thus

pro#iding useul inormation about the subsurace materials (e.g. ca#ities, dense rock,"ointed rock).

The olloing inormation o the rock masses can be inerred rom seismic data$

a) 5ocation & confguration o bed rock and geological structures in the subsurace.


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b) The eHect o discontinuities in rock masses may be estimated by comparing the in situcompressional a#e #elocity ith sonic #elocity o intact drill core obtained rom thesame rock mass.

ISince in situ rock are ractured and "ointed hence, compressional a#e #elocity is loer

compared to intact coreJ

Dased on seismic data o in situ rock mass and intact rock sample, R0 can be estimated$

RQD () >e"$0< %0"

(>F >L)*++

2here$


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T


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Take * m?o a rock mass, ith = "oint sets, M* & M=;#g. spacing, S* 4 1.=;#g. spacing, S= 4 1.?

M# 4 Mi4*(* N Si)

M#4 (*N1.=) O (*N1.?)M#4 6 O ?.?M#4 C.?

R0 4 **6 ?.? M#

R0 4 **6 ?.? C.?R0 4 CC 7

B"0n 2e2 0n %"$6

B"0n 2e2 0n g%n0e ;2;< @ 2e2 B"0n2 n5 "0n 2e2 0n%"$6 B"0n 24$0ng

(A3"2 4e%4en50$;% " e$! "!e%) 02 !e !"%0"n502n$e2 'e=een e$! "0n0n 2e n5 3e2;%e5 "ng

!"%0"n 0ne

Take * m? o rock mass ith three "oint sets,M*, M= and M? (ma"or "oint set only). easurethe spacing beteen each "oint (in a gi#en

set) along ahori8ontal line.

Moint spacing orset M*$ *?6, ==6, ?11 & =1 mm.

;#erage spacing, S*4 =?1 mmMoint spacing or set M= $ ?61 & 61 mm. ;#eragespacing, S=4 11 mm.

Moint spacing or set M?$ =61, =:1, =C1 mm. ;#eragespacing, S?4 =: mm

Moint spacings M*$ *?6, ==6, ?11 & =1 mm.;#erage spacing, S*4 =?1 mm 4 1.=? m

Moint spacings M= $ ?61 & 61 mm.


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;#erage spacing, S=4 11 mm 4 1. m.

Moint spacing M?$ =61, =:1, =C1 mm.;#erage spacing, S?4 =: mm 4 1.=: m(9ote$ unit or a#erage "oint spacing is in metre)

M# 4 *N1.=? O *N1. O *N1.=: 4 *1.1 m

R0 (7) 4 **6 ?.? M# 4 **6 ?.+C 4 C1 7

!ompared to direct method (R0 using core sample),


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The strength o the intact rock material should be obtained rom rock cores, the ratings

based on uniaial compressi#e strength (preerred) & point-load strength as shon inTable *.

Q;00?e5e2$%040"n

C"34%e220?e S%eng!

(MP)

P"0n-"5 2%eng! (MP) R0ng

Aceptionallystrong

Q =61 C *6

oor =6 61 C


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6 mm thick sot gouge, 6 mm ide continuous discontinuity 1T'e : C"n500"n "# 502$"n0n;00e2(80en0=260, *9H9)

() G%";n5 7e% C"n500"n

%n the case o tunnel, the rate o ino o ground ater in litres per minute per *1 m

length o the tunnel should be determined, or general condition can be described ascompletely dry, damp, et dripping & oing.

% actual ater pressure data is a#ailable, these should be stated & epressed in terms o

the ratio o the seepage pressure to the ma"or principal stress.

The ratings as per the ater condition are gi#en in Table 6.%no per *1 m tunnel length(litreNmin)

9one P *1 *1 =6 =6 *=6 Q *=6

Moint ater pressuresNma"orprincipal stress

1 1 1.* 1.* 1.=

1.= 1.6 Q 1.6

@eneral description !ompletelydry

amp 2et ripping 'loing

Rating *6 *1 : 1T'e : G%";n5 =e% $"n500"n(80en0=260, *9H9)

Rating o the abo#e 6 parameters (Table * to Table 6) are added to obtain hat is called

the basic rock mass rating - RRbasic

() O%0en0"n O# D02$"n0n;00e2

Grientation o discontinuities means the %> and STR%UA o discontinuities (eakness

planes).

The dip angle is the angle beteen the hori8ontal and the discontinuity plane taken in a

direction in hich the plane dips.

The #alue o the dip and strike should be recorded as shon in Table , the orientation o

tunnel ais or slope ace or oundation alignment should also be recorded.

;. Grientation o tunnelNslopeNoundation ais$VVVVVVVVVVVVVV.

D. Grientation o discontinuitiesSet * ;#erage strike$ VVVVV. (rom VVVVV toVVVVV) ipVVVVVSet = ;#erage strike$ VVVVV. (rom VVVVV toVVVVV) ipVVVVVSet ? ;#erage strike$ VVVVV. (rom VVVVV toVVVVV) ipVVVVV

T'e : O%0en0"n "# 502$"n0n;00e2

The inuence o the strike & dip o the discontinuities is considered ith respect to thedirection o tunnel dri#age or slope ace orientation or oundation alignment.

To acilitate a decision hether the strike & dip are a#ourable or not, reerence should bemade to Table : & Table C hich pro#ide a /uantitati#e assessment o critical "ointorientation eHect ith respect to tunnels & dams oundation respecti#ely.

Gnce the ratings or the eHect o the critical discontinuity are knon, as shon in Table +

an arithmetic sum o the "oint ad"ustment rating in and the RR basic is obtained. Thisnumber is called the fnal rock mass rating RR.

Strike perpendicular to tunnel Strike parallel to tunnelais

%rrespecti#e ostrike

ri#e ith dip ri#e against dip

ip 6W -

+1W

ip =1W -

6W

ip 6W -

+1W

ip =1W -

+1W

ip =1W -

6W

ip 6W -

+1W

ip 1W -

=1W


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T'e H: A22e223en "# "0n "%0en0"n eJe$ "n ;nne2 - 5042 %e 44%en 5042"ng ;nne 102

(80en0=260, *99)

ip 1W - *1W ip 1W - *1W ip ?1W - 1W ip 1W -+1Wip direction

Bpstream onstreamoor a)X Q 1. 1.? 1. 1.= 1.? 1.* 1.= P 1.*;ngle o internal riction orock mass

Q 6W ?6W - 6W =6W - ?6W *6W - =6W *6W

9ote X These #alues are applicable to slopes only in saturated and eathered rock massT'e *+: De20gn 4%3ee%2 & eng0nee%0ng 4%"4e%0e2 "# %"$6 322 (80en0=260,

*9H9)

Separate RR should be obtained or tunnels o diHerent orientations ater taking intoaccount the orientation o tunnel ais ith respect to the critical "oint sets (Table ).

RR can be used or estimating many useul parameters such as the unsupported span, the

stand-up time (bridging action period) & the support pressure or an underground opening.


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%t can also be used or selecting a method o eca#ation & permanent support system or

underground eca#ation in rock (Dieniaski, *+:).

eormation modulus & alloable bearing pressure may also be estimated.

;. Grientation o tunnelNslopeNoundation ais$VVVVVVVVVVVVVV.

D. Grientation o discontinuities

Set * ;#erage strike$ VVVVV. (rom VVVVV toVVVVV) ipVVVVVSet = ;#erage strike$ VVVVV. (rom VVVVV toVVVVV) ipVVVVVSet ? ;#erage strike$ VVVVV. (rom VVVVV toVVVVV) ipVVVVV

T'e : O%0en0"n "# 502$"n0n;00e2

A440$0"n O# RMR:(*) A?e%ge Sn5-U4 T03e F"% A%$!e5 R""#:

The stand-up time depends upon eHecti#e span o the opening hich is defned as the

idth o the opening or the distance beteen the tunnel ace and the last support,hiche#er is smaller. 'or arched openings the stand-up time ould be signifcantly higherthan that or a at roo.

!ontrolled blasting ill urther increase the stand-up time as damage to the rock mass isdecreased.

%t is important not to delay supporting o the roo in the case o rock ith high stand-up

time, as this may lead to deterioration in the rock hich ultimately reduces the stand-uptime.

Re0"n2!04 'e=een RMR %0ng, 2n5-;4 03e & Un2;44"e5 24n (80en0=260,*99)

() E2030"n O# S;44"% P%e22;%e:

The estimation o support pressure or openings ith at roo is gi#en as (Bnal, *+C?)$

P? (*++ RMR) *++ 82here$ ># $ support pressure

$ rock density

D $ tunnel idth

'or rock tunnel ith arched roo the estimation o short-term support pressure is gi#en as(@oel & Metha, *++*)$

P? (+H 8+*+ RMR) ( RMR) MP


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2here$ ># $ short-term roo support pressure (>a)L $ depth o tunnel in m (Q 61 m)D $ span o opening in m

(ethod o eca#ation by con#entional blasting method) $ !omprehensi#e guidelines

Dieniaski (*+C+) pro#ides a comprehensi#e guidelines or selection o tunnel

stabilisation methods. This is applicable to tunnels eca#ated ith con#entional drill &blast method.

These guidelines depend upon actors like depth belo surace (in situ o#erburden stress)

tunnel si8e & shape & method o eca#ation. The stabilisation measures are thepermanent and not temporary (or primary) support.

E1$?0"n 2!4e: "%2e2!"e 705!: *+3 >e%0$ 2%e22: MP C"n2%;$0"n 3e!"5: D%0n5 '2

Rock assRating

Aca#ation SupportRock bolts (=1mmdia. 'ully bonded)

Shotcrete Steel sets


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>ressure acting on a rock bed due to building oundation should not be more than the sae

bearing capacity o rock oundation system taking into account the eHect o eccentricity.

%t is oten useul to estimate the sae bearing pressure (SD>) or preliminary design on the

basis o the classifcation approach (e.g. RR)

Grientation o "oints plays a dominant role in stress distribution belo strip ooting due to

lo shear modulus o bedrocks. Dearing capacity o rocks ill be drastically lo or near#ertical "oints that strike parallel to the ooting length as pressure bulb etends deep intothe strata see 'igure

Shear 8one and clay gouge, i present belo oundation le#el, need to be treated toimpro#e bearing capacity & reduce diHerential settlement

O%0en0"n "# "0n2 n5 2%e22 502%0';0"n 'e"= 2%04 S030% " !e eJe$"# %"$62 5024


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E2030"n O# A"='e 8e%0ng P%e22;%e U20ng RMR:

The RR system may also be used to obtain net ;D> as proposed by ehrotra (*++=). The

guidelines or the ;D> (Table *?) are$(*) The RR should be obtained belo the oundation at depth e/ual to the idth o the

oundation, pro#ided RR does not change ith depth. % the upper part o the rock,ithin a depth o about one ourth o the oundation idth, is o loer /uality the #alue othis part should be used or the inerior rock should be replaced ith concrete. may be increased by 617 in #ie o

rheological beha#iour o rock masses.C22 N" I II III I> >escription orock

but relati#ely conser#ati#e compared to Table

*. 'or socketed piles & shallo oundations, @ill (*+C1) gi#es the olloing ormula$

;lloable Dearing >ressure, $NN5Rock Type Lighly

eatheredstructureuna#orableor stabilityX

'airlyeatheredstructureuna#orableor stability

Lighlyeatheredstructurea#orable orstability

'airlyeatheredstructurea#orable orstability

Bn-eatheredrockstructureuna#orableor stability

Bn-eatheredrockstructurea#orable orstability

arls, marlsinterbeddedith sandstone

*6 ?1 ?6 61 1 **1

!alc-schist, calc-schistinterbeddedith /uar8ites

*6 ?1 6 6 *11 =11

Slates, phyllites,schistsinterbeddedith hardsandstone &/uart8ite orgneiss

=1 ?6 1 :6 +1 *?1

5imestone,dolomite &marbles

61 C1 +1 *?1 *61 =11

Sandstone 1 1(massi#e)

+1 *=1 *61 *:1 ==1

!alcareousconglomerates(massi#e)

1 *11 *=1 =11 =11 ??1

0uart8ite(massi#e)

61 :1 *61 *=1 *C1 =11 ??1

@neiss(massi#e)

?1 1 *61 *=1 *C1 =11 ??1

@ranite &plutonic rocks =1 =61 Q ??1

T'e *: A"='e P%e22;%e "# ?%0";2 %"$6


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2here$ /c 4 a#g. laboratory uniaial compressi#e strength9"4 empirical coeH. depending on the spacing o discontinuities (see Table *6),

and calculated as$

( ))

s

Bs

jN +

+=

300(110

3

2here$ s 4 spacing o "oint in cmD 4 ooting idth in cm

S4$0ng "# 502$"n0n;00e2, $3 N?11 1.

*11 ?11 1.=6?1 *11 1.*

T'e *: >;e "# B"0n S4$0ng & N#"% e2030"n "# A"='e 8e%0ng P%e22;%e

;lloable Dearing >ressure, $NN5

( ))

s

Bs

jN +

+=

300(110

3

2here$ 4 opening o "oints in cm

9d is 4 1.C O 1.= (hN) P =*.1

4 *.1 or shallo oundations o buildingsh 4 depth o socket in rock 4 diameter o socket

A/uation /a4 /c9"9d may also be applied to shallo oundation considering 9d4 *.1.

%t may be noted that the abo#e correlation does not take into account or orientation o

"oints.

%t is recommended that plate load test should be conducted on poor rocks here ;D> is liketo be less than *11 tNm=.

Bncertainties on ;D> may be impro#ed by a larger number o obser#ation pits, say at a rate

o at least ? pits per important structure. The load test should be conducted in the pitrepresenting the poorest rock /ualities.

C"e$0en "# E20$ Un0#"%3 C"34%e220"n #"% M$!0ne F";n50"n:

The coecient o uniorm compression !u is defned as the ratio beteen pressure and

corresponding settlement o block oundation.

Typical #alues o !uor machine oundation on rock mass are listed in Table *.

The coecient o uniorm shear is generally taken as !uN=. %t may be noted that !uis less

than *1 kgNcm?in #ery poor rocks.R"$6


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Mr 4 Moint roughness number or critical "oint setMa 4 Moint alteration number (eathering) or critical "oint setM 4 Moint reduction actor due to presence o aterSR' 4 Stress reduction actor

'or #arious rock conditions, the numerical ratings or the abo#e parameters are defned as

ollos$

(*) R"$6 ;0< 5e20gn0"n, RQD:

R0 as pre#iously defned. The R0 #alue in 7 is the rating o R0 or the 0-system. %n the case o a poor rock mass here R0 P *17, a minimum #alue o *1 should be used

to e#aluate 0.C"n500"n RQD ();. oor =6 61!. 'air 61 :6.@ood :6 +1A. Acellent +1 *119ote$ (i) 2here R0 is measured as Z *1 (including 1), a nominal #alue o *1 is used to e#aluate0

(ii) R0 inter#als o 6 i.e *11, +6, +1 etc. are suciently accurate

T'e *: R"$6 Q;0< De20gn0"n RQD (8%"n e , *9H)

() B"0n 2e n;3'e% (Bn):

The parameter Mn, representing the number o "oint sets, is oten aHected by oliations,

schistocity or beddings, etc. % strongly de#eloped, these parallel discontinuities should becounted as a complete "oint set.

% there are e "oints #isible or only occasional breaks in rock core due to these eatures,

then one should count them as Ea random "oint setF hile e#aluating M n rom Table =.Rating o Mnis approimately e/ual to s/uare o the number o "oint sets.

C"n500"n (Bn);. assi#e, none or e "oints 1.6

*.1D. Gne "oint set =!. Gne "oint set plus random ?.To "oint set A. To "oint sets plus random '. Three "oint set [email protected] "oint sets plus random *=L.'our [ more "oint sets, random, hea#ily "ointed,

Esugar cubeF, etc.*6

%. !rushed rock earth like =19ote$ (i) 'or intersection use (?.1 Mn) (ii) 'or portals use (=.1 Mn)

T'e : B"0n 2e n;3'e% Bn(8%"n e , *9H)

(@) B"0n R";g!ne22 & B"0n Ae%0"n N;3'e% (B% & B):

The parameters Mr& Ma, gi#en in Table ? & Table , respecti#ely, represent roughness &degree o alteration o "oint alls or flling materials.

The parameters Mr& Ma, should be obtained or the eakest critical "oint-set or clay-flled

discontinuity in a gi#en 8one.C"n500"n B%a) Rock all contactb) Rock all contact beore *1cm shear

;. iscontinuous "oint

D. Rough or irregular, undulating!. Smooth, undulating.Slickensided, undulatingA. Rough or irregular, planar'. Smooth, planar

.1

?.1=.1*.6*.6*.1


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@.Slickensided, planar 1.6c) 9o rock all contact as sheared

L.\one containing clay minerals thick enough to pre#ent rockall contact

%. Sandy, gra#elly or crushed 8one thick enough to pre#ent rockall contact

*.1*.1

9ote$ (i) ;dd *.1 i the mean spacing o the rele#ant "oint set is greater than ?.1m (ii) Mr 4 1.6 can be used or planar, slickensided "oint ha#ing lineation, pro#ided the lineationare a#orable orientated.

(iii) escription D to @ abo#e reer to small scale and intermediate scale eatures, in thatorder.

T'e @: B"0n %";g!ne22 n;3'e% B%(8%"n e , *9H)C"n500"n % Ba) Rock all contact

;. Tightly healed, hard, non-sotening, impermeable flling (e.g. /uart8 [epidote).

D. Bnaltered "oint alls, surace staining only.!. Slightly altered "oint alls. 9on-sotening mineral coatings, sandy

particles, clay-ree disintegrated rock, etc..Slickensided, undulating.A. Sotening [ lo-riction clay mineral coatings (e.g. kaolinite, mica).

;lso chlorite, talc, gypsum & graphite etc. & small /uantities oselling clays (discontinuous coating * to =mm [ less in thickness).

=6W -?6W

=6W -?1W

=1W -=6WCW -*W

1.:6*.1=.1

?.1.1

b) Rock all contact beore *1cm shear'. Sandy particles, clay-ree disintegrated rock, [email protected] o#er-consolidated, non-sotening, clay mineral flling

(continuous, P 6mm in thickness).L.edium [ lo o#er-consolidation, sotening, clay mineral flling

(continuous, P 6mm in thickness).M. Selling clay fllings, e.g. montmorillonite (continuous, P 6mm in

thickness).


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T'e H (RMR): A22e223en "# "0n "%0en0"n eJe$ "n ;nne2 (5042 %e 44%en5042 "ng ;nne 102) (80en0=260, *99)

() B"0n 7e% Re5;$0"n F$"% (B=):

The parameter M(Table 6) is a measure o ater pressure, hich has an ad#erse eHect on

the shear strength o "oints. This is due to reduction in the eHecti#e normal stress actingacross "oint surace.

2ater in addition may cause sotening & possible ash-out in the case o clay-flled "oints.

2ater may also acts as lubricant (reducing shear strength) and causes selling omontmorillonite.

C"n500"n A44"103e=e%

4%e22;%e,MP

B=

;. ry eca#ations [ minor ino, i.e. 6litreNmin locally.D. edium ino [ pressure occasional out-ash o "oint

fllings.!. 5arge ino [ high pressure in competent rock ith unflled

"oints.

.5arge ino [ high pressure, considerable out-ash o "ointfllings.A. Aceptionally high ino [ ater pressure at blasting

decaying ith time.'. Aceptionally high ino [ ater pressure continuing

ithout noticeable decay.

P 1.*11.*1 1.=61.=6 *.111.=6 *.11

Q *.11

Q *.11

*.111.1.611.??1.=

1.*1.* 1.16

9ote$ 'actors ! to ' are crude estimates. %ncrease Mi drainage measures are installed.

T'e : B"0n =e% %e5;$0"n #$"% B=(8%"n e , *9H)

() S%e22 Re5;$0"n F$"% (SRF):

The parameter SR' (Table ) is a measure o the olloings$

i) 5oosening pressure in the case o an eca#ation through shear 8ones & clay bearing

rock masses.ii) Rock stress /cN*in a competent rock mass here /cis uniaial compressi#e strength o

rock material & *is the ma"or principal stress beore eca#ation.iii)S/uee8ing or selling pressures in incompetent rock masses & SR' can also be

regarded as a total stress parameter.C"n500"n SRFa) 2eakness 8ones intersecting eca#ation, hich may cause loosening o rock mass hen

tunnel is eca#ated.;. ultiple occurrences o eakness 8ones containing clay [ chemically

disintegrated rock, #ery loose surrounding rock (any depth).D. Single-eakness 8ones containing clay [ chemically decomposed rock (depth o

eca#ation Z 61m).!. Single-eakness 8ones containing clay [ chemically decomposed rock (depth oeca#ation Q 61m).

.ultiple-shear 8ones in competent rock (clay-ree), loose surrounding rock (anydepth).

A. Single-shear 8ones in competent rock (clay-ree), (depth o eca#ation Z 61m).'. Single-shear 8ones in competent rock (clay-ree), (depth o eca#ation Q 61m)[email protected] open "oints, hea#ily "ointed [ Esugar cubeF, etc. (any depth).

*1.1

6.1

=.6:.66.1=.66.1

9ote$ Reduce these SR' #alues by =6 617 i the rele#ant shear 8ones only inuence but do not intersect theeca#ation.

C"n500"n $* * SRF("5)

SRF(ne=)

b) !ompetent rock, rock stress problemsL.5o stress, near surace open "oints.

M. edium stress, a#orable stress condition.U. Ligh stress, #ery tight structure (usually

a#orable to stability, may be una#orable to

Q =11=11

*1*1 6

P 1.1*1.1*

1.?1.? 1.

=.6*.1

1.6 =

=.6*.1

1.6 =


20/21

all stability).5. oderate slabbing ater Q * hour in massi#e

rock..Slabbing & rock burst ater a e minutes in

massi#e rock.9.Lea#ily rock burst (strain-burst) & immediate

deormations in massi#e rock.

6 ?? =P =

1.6 1.6

1.6 *.1Q *

6 ++ *6

*6 =1

6 6161 =11

=11 11

9ote$

(i) 'or strongly anisotropic stress feld (i measured)$ hen 6 Z (*N?) Z *1, reduce /c & /t to 1.C/c& 1.C/tK hen

(*N?) Q *1, reduce /c & /t to 1./c& 1./t(here /c is unconfned compressi#e stress & /t is tensile strength

(point load), * & ? are ma"or & minor principal stress).(ii) 'e case records a#ailable here depth o cron belo surace is less than span idth. Suggest SR' increase

rom =.6 to 6 or such cases (see L).

C"n500"n SRFc) S/uee8ing rockK plastic o o incompetent rock under the inuence o high pressures.

G.ild s/uee8ing rock pressure.>. Lea#y s/uee8ing rock pressure.

6 *1*1 =1

d) Selling rockK chemically selling acti#ity depending on presence o ater.0.ild selling rock pressure.R. Lea#y selling rock pressure.

6 *1*1 *6

9ote$(i) Reduce these SR' #alues by =6 617 i the rele#ant shear 8ones only inuence but do not intersect theeca#ation.(ii) 'or getting the rating o SR' in case o s/uee8ing ground condition, the degree o s/uee8ing can be obtainedrom Table :.6.

T'e : S%e22 Re5;$0"n F$"% SRF (8%"n e , *9H G%0325 & 8%"n, *99@)

Ratings o all the parameters (as gi#en in Table * to Table ) or gi#en rock mass aresubstituted in the e/uation to get the rock mass /uality$

Q RQDBn B%B B=SRF

The 0-system may be considered a unction o only ? parameters hich are approimate

measures o$*) Dlock si8e IR0NMnJ$

%t represents o#erall structure o rock mass.=) %nterblock shear strength IMrNMaJ$

%t has been ound that tan -* IMrNMaJ is a air approimation to the actual peak sliding angle oriction along the clay coated "oint (see Table :).

?) ;cti#e stress IMNSR'J$%t is a actor describing the acti#e stress.

escription tan-* (MrNMa)a) Rock all contact Mr Ma 4 1.:6 Ma 4 *.1 Ma 4 =.1 Ma 4 ?.1 Ma 4 .1

;. iscontinuous "ointD. Rough, undulating!. Smooth, undulating

.Slickensided, undulatingA. Rough, planar'. Slickensided, planar

.1?.1=.1

*.6*.61.6

:+W:1W+W

?W?W?W

:W:=W?W

6W6W=:W

?W6W6W

?:W?:W*W

6?W6W?W

=:W=:W+.6W

6W?:W=:W

=*W=*W:.*W

b) Rock all contact hensheared

Mr Ma 4 .1 Ma 4 .1 Ma 4 C.1 Ma 4 *=.1

;. iscontinuous "ointD. Rough, undulating!. Smooth, undulating.Slickensided, undulatingA. Rough, planar'. Slickensided, planar

.1?.1=.1*.6*.61.6

6W?:W=:W=*W=*W:W

?W=:W*CW*W*W.:W

=:W=*W*W**W**W?.W

*CW*W+.6W:.*W:.*W=.W

c) 9o rock all contact hensheared Mr Ma 4 .1 Ma 4 C.1 Ma 4 *=.1

isintegrated or crushed rock[ clay

*.1 +.6W :.*W .:WMr Ma 4 6.1*.1 **W


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Documents

Part 09 - Classification of Rock Mass