+ All Categories
Home > Documents > Chp 11 (Rock Stabilisation)

Chp 11 (Rock Stabilisation)

Date post: 04-Apr-2018
Category:
Upload: tuan-jalai
View: 229 times
Download: 0 times
Share this document with a friend

of 47

Transcript
  • 7/31/2019 Chp 11 (Rock Stabilisation)

    1/47

    Const ruc t ion cost o f s t ruc t ures (tunne l & s lope)Const ruc t ion cost o f s t ruc tures (tunne l & s lope)

    w i l l increase i f they need some m ethods o fw i l l increase if they need some m ethods o f

    s tab i l i sa t ionstab i l i sa t ion . The cost w i l l increase fur ther i f the. The cost w i l l increase further i f the

    stab i l i sa t ionstab i l i sa t ion is ofis of h igher degreehigher degree & t o be& t o be

    main ta ined for amain t a ined for a long per iod o f t im elong per iod o f t im e .. Appropr ia teAppropr ia te

    designdesign && cons t ruc t ion methodcons t ruc t ion method help to reduce thehe lp to reduce t he

    amount & c os t o fam oun t & cos t o f s tab i l i sa t ionstab i l i sa t ion ..

    Des ign & const ruc t ion met hod thatDes ign & const ruc t ion met hod that are notare not

    accord ing t oaccord ing t o cor rec t procedurescor rec t proc edures w i l l i nducew i l l i nduce

    s ign i f icant d is turbance ( th ick er y ie ld zone) in rocks ign i f icant d is turbance ( th ick er y ie ld zone) in rockmassmass consequent ly w i l l requ i re a h igher leve l o fconsequent ly w i l l requ i re a h igher leve l o f

    s tab i l i sa t ionstab i l i sa t ion & h igher cos t !& h igher cos t !

    As soon as a tunnel is excavated, surrounding rock mass will beAs soon as a tunnel is excavated, surrounding rock mass will be

    disturbeddisturbedformation offormation ofyield zoneyield zone. Design & method of construction. Design & method of construction

    must be carefully considered so that disturbance to surroundingmust be carefully considered so that disturbance to surrounding

    rock is reduced (thinner yield zone, less affected volume).rock is reduced (thinner yield zone, less affected volume).

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    2/47

    As soon as a slope is excavated, surrounding rock mass will beAs soon as a slope is excavated, surrounding rock mass will bedisturbeddisturbedformation offormation ofyield zoneyield zone. Design & method of construction. Design & method of construction

    must be carefully considered so that disturbance to surroundingmust be carefully considered so that disturbance to surrounding

    rock is reduced (thinner yield zone, less affected volume).rock is reduced (thinner yield zone, less affected volume).

    Geologica l m app ing & jo in t surveyGeologica l m app ing & jo in t survey

    In format ion l ike t ypes o f discont inu i ty andIn format ion l ike t ypes o f discont inu i ty and

    the i rthe i r geometr ica l cond i t ionsgeometr ica l cond i t ions (d ip & d ip(d ip & d ip

    d i rec t ion) are essent ia l fo r in i t ia l ind icat ionsd i rec t ion) are essent ia l fo r in i t ia l ind icat ions

    on modes o f ins t ab i l i ty , s ize o f unstab le b lock son modes o f ins t ab i l i ty , size o f unstab le b lock s

    & d i rec t ion o f s l id ing that can be expect ed& d i rec t ion o f s l iding that can be expected

    upon excavat ion o f the rock mass ( for tunne lupon excavat ion o f the rock mass ( for tunne l

    or s lope)or s lope)

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    3/47

    Take a very s t rong rock mass, cont inuous (sol id ,Take a very s t rong rock mass, cont inuous (so l id ,

    no w eakness p lanes/d iscont inu i t ies) & f reshno w eakness p lanes/d iscont inu i t ies) & f resh

    ((unweatheredunweathered, Zone 1), Zone 1)

    Note: s lope height , HNote: s lope height , H [UCS/[UCS/]]

    Can a near vert ic a l s lope be excavated in t h isCan a near vert ic a l s lope be excavated in t h is

    rock mass, any prob lem on s tab i l i ty???rock mass, any prob lem on s tab i l i ty???

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    4/47

    . . . . . in te rm s of. . . . . in te rm s of rock m ass proper t iesrock m ass proper t ies o f theof the

    idealideal rock , a ver t ica l s lope is poss ib lerock , a ver t ica l s lope is poss ib le

    e.g. for grani t e (UCS = 120e.g. for granit e (UCS = 120 MPaMPa ,, = 26 k N/m= 26 k N/m 33 ))

    s lope o f few km h igh is poss ib le ! !!s lope of few km high is possib le !! !

    But rock mass is a lways d iscont inuous, more thanBut rock mass is a lways d iscont inuous, more than

    one type o f d iscont inu i t ies a t d i f fe rent or ienta t ionsone type o f d iscont inu i t ies a t d i f fe rent or ienta t ions

    Rock typesTypes of structural

    discontinuityIgneous Sedimentary Metamorphic

    Fault plane

    Joint plane

    Bedding plane

    Foliation

    Slaty & schistosity

    Type & s ize o f d iscont inu i t ies m ay ind icate s ize o fType & s ize o f d iscont inu i t ies m ay ind icate s ize o f

    unstable b loc ks. In general , in term s of s ize, theunstable b loc ks. In general , in term s of s ize, the

    largest is faul t , fo l low ed by bedding plane, and thelargest is faul t , fo l low ed by bedding plane, and the

    smal les t is jo in tsmal les t is jo in t

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    5/47

    Typical s lope fac e . .. . d isc ont inuous, f resh (GradeTypical s lope fac e . .. . d iscont inuous, f resh (Grade

    I ) to com ple te ly w eathered (Grade V) rock massI ) to com ple te ly w eathered (Grade V) rock mass

    A s lope fac e cut in a f resh (zone 1) and veryA s lope fac e c ut i n a f resh (zone 1) and verys t rong rock mass but ,s t rong rock mass but , w i th hor izonta l bedd ingw i th hor izonta l bedd ing

    planesplanes (discont inui t y or w eakness plane) . . . . .(d iscont i nui ty or w eakness plane) . . . . .

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    6/47

    Wil l the s tab i l i ty o f t he cut s lope be a f fec ted byWil l the s tab i l i t y o f the cut s lope be af fec ted by

    the hor izontal bedding planes?the hor izontal bedding planes?

    Is there any immedia te e f fec t due toIs there any imm edia te e f fec t due to rock massrock massproper t iesproper t ies && bedding planesbedding planes ??

    A s lope face cut in f resh & s t rong rock m assA s lope face cut in f resh & s t rong rock m ass

    w i th hor izonta l bedd ing p lanes and inc l inedw i th hor izonta l bedd ing p lanes and inc l ined

    fract ure p lanes (e.g. jo ints)f rac ture p lanes (e.g. jo int s)

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    7/47

    For s lope (A), is the st abi l i t y being af fect ed by theFor s lope (A), is the st abi l i t y being af fect ed by the

    hor izontal beddinghor izontal bedding && inc l ined jo in t p lanesinc l ined jo in t p lanes??

    Let propose anot her s lope (B) on the ot her s ide ofLet propose anot her s lope (B) on the ot her s ide of

    t he hi l l . . . .t he hi l l . . . .

    SLOPE A

    SLOPE B

    The rock propert ies & the hor izonta l bedd ingThe rock propert ies & the hor izonta l bedd ing

    p lanes have no imm edia te e f fec t on the s t ab i l i typ lanes have no imm edia te e f fec t on the s tab i l i t yof bot h SLOPE A and B.of bot h SLOPE A and B .

    However, w i th respec t t o theHowever , w i th respec t to t he or ienta t ionor ienta t ion of theof the

    incl i ned jo ints, SLOPE B is cr i t ica linc l ined jo int s, SLOPE B is cr i t ica l

    SLOPE A SLOPE B

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    8/47

    Ef fec t o f d ip & d ip d i rec t ion o f w eakness p lanes onEf fec t o f d ip & d ip d i rec t ion o f w eakness p lanes on

    stab i l i ty o f s lope face in a d iscont inuous rockstab i l i ty o f s lope face in a d iscont inuous rock

    Di f fe rent mode o f ins tab i l i ty requ i res d i f fe rentDi f fe rent mode o f ins tab i l i ty requ i res d i f fe rent

    s tab i l i sa t ionstab i l i sa t ion met hod hence, i t i s impor tant t omethod hence , i t i s im portan t to

    unders tandunders tand 2 aspect s2 aspect s before one can se lec t anbefore one can se lec t an

    e f fec t i ve m ethod :e f fec t ive method:

    What is t he mode o fWhat is t he mode o f preva il ing ins tab i l i t ypreva i ling ins t ab i l i ty (plane,(plane,

    w edge, f lexura l or rock fa l l )?w edge, f lexura l or rock fa l l )?

    HowHow spec i f icspec i f ic s tab i l i sa t ionstab i l i sa t ion m e thod w o rksmethod w orks

    (mechanisms) to produce e f fec t ive s tab i l i ty?(mec hanisms) to produce e f fec t ive s tab i l i ty?

    Mos t rockMost rock stab i l i sa t ionstab i l i sa t ion met hods are d if fe rent f rommet hods are d if fe rent f rom

    those used in so i ls . Th is is main ly due t o t hethose used in so i ls . Th is is m ain ly due to t he modemode

    of ins tab i l i ty in rockof ins tab i l i ty in rock (the less w eathered ones)(the less w eathered ones)

    w h ich i s a lways assoc ia ted w i th w eakness p lanesw h ich i s a lways assoc ia ted w i th w eakness p lanes

    rather than i ts mater ia l s t rengthra ther than i ts mat er ia l s t rength

    I nstab i l i t y in rock & method o fInstab i l i t y in rock & method o f s tab i l i sa t ionstab i l i sa t ion

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    9/47

    To he lp the rock massTo he lp the rock mass to suppor t i tse l fto suppor t i tse l f byby

    improv ing stab i l i ty & main t a in ing theimprov ing s tab i l i ty & main t a in ing the loadload --

    car ry ing capabi l i ty o f rockcar ry ing capabi l i ty o f rock near the boundar iesnear the boundar ies

    of exc avat ion (w i t h in the y ie ld zone!)o f exc avat ion (w i t h in the y ie ld zone!)

    ToTo mobi l isemobi l ise && conserveconserve t het he inherent s t rengthinherent s t rength

    o f rock mass so tha t i t becomeso f rock mass so tha t i t becomes sel fsel f --

    suppor t ingsuppor t ing!!

    Pr inc i p les of roc kPr inc ip les of roc k s tab i l i sa t ionstab i l i sa t ion methodsmethods

    Pr inc ipa l ly in rock s lope w e need toPr inc ipa l ly in rock s lope w e need to s tab i l i ses tab i l i se onlyonly

    the unstab le keythe unstab le key --b locks, not the w hole rock mass! !b locks, not the w hole rock m ass!!

    I n so i l , due to w eak bond ingIn so i l , due to w eak bond ing

    betw een so i l g ra ins , thebetw een so i l g ra ins , the

    w eakness p lanesw eakness p lanes areare

    th roughout the so i l mass &throughout the so i l mass &

    in every d i rect ion, you needin every d i rect ion, you need

    t ot o s tab i l i ses tab i l i se the w ho le slope .the w ho le s lope .

    th is is why method l i ket h i s i s why m e t hod l i ke

    re ta in ing w a l lre ta in ing w a l l is notis not

    p rac t ica l f o r rock s lope .prac t ic a l f o r rock s lope .

    The pr inc ipa lThe pr inc ipa l t ot o mob i l i semob i l i sethe inheren t s t reng th sothe inheren t s t reng th so

    tha t the rock c an suppor ttha t the rock c an suppor t

    i t se l f !i t se l f !

    K eyK ey --b locksb locks

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    10/47

    Ef fec t o f conf inement on h igh ly jo in ted rockEf fec t o f conf inement on h igh ly jo in ted rock

    Conf in ing pressureConf in ing pressureinc reases con tac t sinc reases con tac t s

    betw een loose unstab lebetw een loose unstab le

    b locks, consequent ly th isb locks, consequent ly th is

    increases f r ic t iona lincreases f r ic t iona l

    s t rength betw een unstab les t rength betw een unstab le

    jo int b loc k sjoint b loc k s increaseincrease

    res is t ing forcesres is t ing forces

    Usual lyUsual ly s tab i l i sa t ionstab i l i sa t ion of s t ruc t ure is an aspecto f s t ruc t ure is an aspect

    tha t m us t be imp lemented.tha t m us t be imp lemented .

    Stab i l i sa t ionStab i l isa t ion met hod is bas ica l ly to increasemet hod is bas ica l ly to inc rease

    FOS, by inc reasing resist ing forc esFOS, by inc reasing resist ing forc es

    FOS = [S resist ing for c es] / [S distu rbingFOS = [S resis t ing forc es] / [S distu rbing

    forces] .fo rces] .

    Disturbing forcesDisturbing forces are fac t o rs tha t somet imesare fac t o rs tha t somet imes

    beyond our c ont ro l (beyond our cont ro l (uncer ta in t iesuncer ta in t ies )) ra infa l l ,ra infa l l ,

    w eather ing ra te , groundwat er , rock m ass,w eather ing ra te , groundwat er , rock m ass,

    ear thquakes e tc .ear thquakes e tc .Resist ing forcesResist ing forces are methods that can beare methods that c an be

    implement ed to increase FOSimplement ed to increase FOSs lope prof i les,s lope prof i les,

    avo id ing prob lem areas & ins ta l l ingavo id ing prob lem areas & ins ta l l ing

    s tab i l i sa t ionstab i l i sa t ion methodmethod

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    11/47

    Considerat ions for se lec t ingConsiderat ions for select ing stab i l i sa t ionstab i l i sa t ion methodmethod ::

    (1) Types, s ize and geomet r ic al or ientat ion of(1) Types, s ize and geomet r ical or ient at ion of

    w eakness p lanes in rock ( jo in t , fau l t & beddings.w eakness p lanes in rock ( jo in t , fau l t & beddings.(2) Mode/type of inst abi l i t y in rock m ass (p lane,(2) Mode/type of inst abi l i t y in rock mass (p lane,

    w edge, f lexura l & rock fa l l ). The mode o fw edge, f lexura l & rock fa l l ). The mode o f

    unstab i l i tyunstab i l i ty is d ic ta t ed by the type, or ienta t ion andis d ic ta t ed by the type, or ienta t ion and

    sets o f w eakness p lane.sets o f w eakness p lane.

    (3) Understanding of the re inforc em ent(3) Understanding of the re inforc ement

    mec hanisms (re in forc ing m ode) o f each m ethodmec hanisms (re in forc ing m ode) o f each m ethod

    i .e . how each e lement reac t s w i th t he ex is t ingi .e . how each e lement reac t s w i th t he ex is t ing

    inst abi l i t y so to inc rease FOS.inst abi l i t y so to inc rease FOS.

    (4) Type of rock , s t r engths, w eather ing grade (HW(4) Type of rock , s t rengt hs, w eather i ng grade (HW

    & CW). Weaker rock s l ike sc h is t & h igh ly& CW). Weaker rock s l ike sc h is t & h igh lyw eathered gran i te are not su i tab le to bew eathered gran i te are not su i tab le to be

    re info rced w i t hre info rced w i th rockbo l trockbo l t & dow e l .& dow e l.

    Mode o f ins tab i l i ty in rock is cont ro l led by type,Mode o f ins tab i l i ty in rock is cont ro l led by type,

    number o f se t and or ienta t ion o f w eakness p lanes.number o f se t and or ienta t ion o f w eakness p lanes.

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    12/47

    Plane fa i lurePlane fa i lure is normal ly assoc ia ted w i th a lmostis normal ly assoc ia ted w i th a lmostpara l lel inc l ined d iscont inu i t ies ( inc l ined beddingpara l lel inc l ined d iscont inu i t ies (inc l ined bedding

    plane in fo ld or faul t ) . The unstable b loc ks areplane in fo ld or faul t ) . The unstable b loc ks are

    usual ly re lat ively larger in s izeusual ly re lat i vely larger in s ize

    More than 3 sets o f in tersect ing jo in ts m ay resu ltMore than 3 sets o f in tersect ing jo in ts m ay resul t

    in rock fa l l (smal ler rock b loc ks) w h ich eventua l lyin rock fa l l (smal ler rock b loc ks) wh ic h eventua l ly

    producing or larger fa i lure (produci ng or larger fa i lure (ravel l ingravel l ing ). Nea r). Nea r

    ver t ica l jo in t se t produces f lexura l topp l ingver t ica l jo in t se t produces f lexura l topp l ing

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    13/47

    A single larger s ize jo int ( in grani te) can lead t oA s ingle larger s ize jo int ( in grani te) can lead to

    p lane fai lu re , and tw o in tersect jo in ts may lead top lane fai lu re , and tw o in tersect jo in ts may lead to

    w edge fa ilu rew edge fai lu re

    I f res is t ing force >> d isturb ing force,I f res is t ing force >> d isturb ing force, s tab i l i sa t ionstab i l i sa t ion

    may not be requ i red. How ever ,may not be requ i red. How ever , longlong --te rm e f fec tte rm e f fec t

    must a lso be cons idered e .g . wat er reducesmust a lso be cons idered e .g . wat er reduces nn ,,

    && ( it ac ts as lubr icant on jo in t sur face)(i t ac ts as lubr icant on jo in t sur face)

    Disturbing force:mg s in

    Resist ing force:jo int = n t an

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    14/47

    Sl id ing is l i ke ly t o occ ur a long jo in tSl id ing is l i ke ly t o occ ur a long jo in t -- shear tes tshear tes t

    is to obt a in shear s t rength o f t he jo in tis to obt a in shear st rength o f t he jo in t

    Larger unstableLarger unstable

    b locks res t ing on anb locks res t ing on an

    inc l ined jo in t orinc l ined jo in t or

    bedding plane canbedding plane can

    lead to p lanelead to p lane

    fai lu re. Whenfai lu re. When

    w eakness p lanesw eakness p lanes

    in te rsec t i t m ayin te rsec t i t m ay

    lead to wedgelead to w edge

    fai lure.fa i lure.

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    15/47

    Plane fa i lure + rock fa l lP lane fa i lure + rock fa l l

    3 or more in tersect ing jo in t se ts t hat are c lose ly3 or more in tersect ing jo in t se ts t hat are c lose ly

    spaced m ay produce smal ler loose/unstable roc kspaced m ay produce sm al ler loose/unstab le rock

    b lock s w h ich may lead to rock fa ll sb lock s w h ich may lead to rock fa l ls

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    16/47

    Rock fa l l (note : some of the rock por t ion has beenRock fa l l (note : some of t he rock por t ion has been

    w eathered to so i l mat er ia l then, fa i lu re mode isw eathered to so i l mat er ia l then, fa i lu re mode is

    s imi lar t o so i l s lope)s imi lar t o so i l s lope)

    Rock fa l lRock fa l l

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    17/47

    Rock fa l lRock fa l l

    Combinat ion o f severa l smal l & la rge s izeCombinat ion o f several sm al l & la rge s ize

    in tersect ing jo in ts may produce combinat ion o fin tersect ing join ts may produce combinat ion o f

    ins tab i l i ty ; rock fa l ls + w edge fa i lu reins tab i l i ty ; rock fa l ls + w edge fa i lure

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    18/47

    Rock s lope fa ilu re a t NKVERock s lope fa ilu re a t NKVE w edge fa i lure + rockw edge fa i lu re + rock

    fa l ls , assoc ia ted w i th 2 in tersect ing fau l ts andfa l ls , assoc ia ted w i th 2 in tersect ing faul ts and

    several jo in t se t sseveral jo in t se t s

    I t i s aI t is a w edge fa ilu rew edge fa i lu re

    due to tw o in te rsec t ingdue to tw o in te rsec t ing

    faul t p lanes (a major &faul t p lanes (a major &

    comm on d iscon t inu i t y )comm on d iscon t inui t y )

    in gran i te rock .in gran i te rock .

    The w edge w eighsThe w edge w eighs

    a lmost 1000almost 1000 tonnetonne ..

    One or tw o jo in t se ts that are in near ver t ic a lOne or tw o jo in t se ts that are in near ver t ic a l

    pos i t ion can produce f lexura l t opp l ingpos i t ion can produce f lexura l t opp l ing

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    19/47

    Stab i l isa t ionStab i l isa t ion and re inforcement o f rockand re in forcement o f rock ::

    The basic pr inc ip le o f rock massThe basic pr inc ip le o f rock mass stab i l i sa t ionstab i l i sa t ionmethod i s tomethod i s to he lp rock m ass tohe lp rock m ass to s tab i l i ses tab i l i se i tse l fi tse l f ..

    Cor rec t ins t a l la t ion o f method c an he lp toCorrec t ins ta l la t ion o f method can he lp to

    mobi l isemobi l ise t het he inherent / in terna l s t rengthinherent / in terna l s t rength avai lableavai lable

    in the roc k (e .g . f r ic t iona l or res idua l s t rength o fin the rock (e.g . f ric t iona l or res idua l s t rength o f

    f rac tured rock , shear s t rength o f d iscont inu i t ies).f rac tured rock , shear s t rength o f d iscont inu i t ies).

    RockRock stab i l i sa t ionstab i l i sa t ion met hods are d iv ided in to 2met hods are div ided in to 2

    main groups:main groups:

    (1) SUPPORT SYSTEM ((1) SUPPORT SYSTEM (penyokongpenyokong))

    (2) REINFORCEMENT SYSTEM ((2) REINFORCEMENT SYSTEM (pengukuhanpengukuhan ))

    SUPPORT SYSTEM:SUPPORT SYSTEM:The use of support e lem ents (e.g. s teel UThe use of support e lem ents (e.g. s teel U --sect ion,sect ion,

    prepre --cast s labs,cast s labs, sho tc re tesho tc re te && wi remeshwi remesh ) that are) that are

    ins ta l led onins ta l led on rock su rfacerock su rface . Th is sys tem increase. Th is sys tem increase

    the s tab i l i ty o f rock body bythe s tab i l i ty o f rock body by impos ing a c onf in ingimpos ing a c onf in ing

    pressurepressure in to t he rock . The c onf in ing pressurein to t he rock . The conf in ing pressure

    increases the contac t betw een f rac ture sur facesincreases the contac t betw een f rac t ure sur faces

    (jo in ts ) and consequent ly e levate t he ex is t ing(jo in ts ) and consequent ly e levate t he ex is t ingf r ic t iona l s t rength in the f rac tured rock .f r ic t iona l s t rength in the f rac t ured rock .

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    20/47

    UU --sect ion/s tee l archsect ion/s tee l arch support met hods ins ta l led onsupport met hods insta l led on

    tunnel sur face. For e f fec t iveness the sys tem musttunne l sur face. For e f fec t iveness the sys tem must

    bebe ac t i veac t i ve (i t m ust y ie lds a long w i th the m ovement(i t m ust y ie lds a long w i th the movem ent

    of sur round ing rock upon t unne l excavat ionof sur round ing rock upon t unne l excavat ion

    Stab i l isa t ionStab i l isa t ion of large tunnel us ingof large tunnel us ing sho tc re tesho tc re te ++

    concret e s lab + rock bo l t + w i re meshconc rete s lab + rock bo l t + w i re mesh

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    21/47

    St eel USteel U --sect ion as suppor t w i th conc rete s labssect ion as suppor t w i th concret e s labs

    as l in ing in betw een the Uas l in ing in betw een the U --sect ionssect ions

    In ter lock ing preIn ter lock ing pre --cas t conc re tecas t conc re te

    s lab as tunne l l in ing & supports lab as tunne l l in ing & support

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    22/47

    Shotcre teShotcre te is to reduce in f i l t ra t ion o f sur face runis to reduce in f i l t ra t ion o f sur face run --of fof fw ater in to the s lope & occ as ional ly to preventw ater in to the s lope & occ as ional ly to prevent

    fa l l ing of smal ler rock b lock s. Bonding betw eenfa l l ing of smal ler rock b locks. Bonding betw een

    t het he sho tc re tesho tc re te & rock su r face mus t be s t rong o r& rock su r face mus t be s t rong o r

    o therw ise theo therw ise the sho tc re tesho tc re te w i l l de tachw i l l de tach

    Mix ing o fMix ing o f sho tc re tesho tc re te

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    23/47

    Stee l w e lded mesh to res t ra in smal ler s izeStee l w e lded mesh to res t ra in smal ler s ize

    unstab le rock b lock s f rom fa l l ing dow n espec ia l lyunstab le rock b locks f rom fa l l ing down espec ia l ly

    t het he k eyk ey --b locksb locks . Fa l l ing o f smal ler rock b loc ks. Fa l l ing o f smal ler rock b loc ks

    may lead t o a larger s lope fa i luremay lead t o a la rger s lope fa i lure -- ravel l ingravel l ing ..

    Spraying ofSpraying of sho tc re tesho tc re te on rock su r face w h ich hason rock sur face w hich has

    been f ixed w i th w elded mesh.been f i xed w i th w e lded mesh . Shotcre teShotcre te isis

    impermeable , thus w eepimperm eable , thus w eep--ho les must be ins ta l ledho les must be ins t a l led

    to dra in w ater out o f the s lopeto dra in w ater out o f the s lope

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    24/47

    Shotcre teShotcre te + wi re m esh + w eep ho les .+ w i re m esh + w eep ho les .

    Shotcre teShotcre te + w eep ho les.+ w eep ho les.

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    25/47

    Shotcre teShotcre te is a lso app l ied on t unne l sur face tois a lso app l ied on t unne l sur face t oincrease s tab i l i ty ( fa l ling o f smal l key roc kincrease s tab i l i ty ( fa l l ing o f smal l key roc k

    b lock s ) & to reduce in f low o f g roundw ate rb locks ) & to reduce in f low o f g roundwate r

    SinceSince sho tc re tesho tc re te is impermeab le to wa t e r i t mus t beis impermeab le to wa t e r i t mus t be

    insta l led w i th w eepinsta l led w i th w eep--ho les . Th is to dra in w ater outho les . Th is to dra in w ater out

    o f the s lope or o therwise t here w i l l be bu i l to f the s lope or o therwise t here w i l l be bu i l t --up ofup of

    porepore --w ater pressure in the s lopew ater pressure in the s lope

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    26/47

    The difference in properties between soil and rock must beThe difference in properties between soil and rock must beunderstood, methods applicable to rock may not be suitable forunderstood, methods applicable to rock may not be suitable for

    soil (or weak rock e.g. schist)soil (or weak rock e.g. schist)shotcreteshotcrete is only applicable foris only applicable for

    strong rock for good bonding betweenstrong rock for good bonding between shotcreteshotcrete & slope face& slope face

    SteelSteelwiremeshwiremesh (chain(chain--link or welded mesh) is used to restrainlink or welded mesh) is used to restrain

    smaller size unstable rock blocks from falling down especially tsmaller size unstable rock blocks from falling down especially thehe

    keykey--blocksblocks. Falling of smaller rock blocks may lead to a larger. Falling of smaller rock blocks may lead to a larger

    slope failureslope failure -- ravellingravelling..

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    27/47

    Rock bo l t o r dow el is used to secure/anchor theRock bo l t o r dow el is used to secure/anchor the

    w i re mesh on rock sur face. I f th is anchorage isw i re mesh on rock sur face. I f th is anchorage isnot e f fec t ive (bol t ing in weak rock ) then, the w i renot e f fec t ive (bo l t ing in weak rock ) then, the w i re

    mesh may be detached f rom the rock sur face &mesh may be detached f rom t he rock sur face &

    become inef fec t ivebecome inef fec t ive

    REINFORCEMENT SYSTEM:REINFORCEMENT SYSTEM:The use o f re in forcement e lements (e .g . dowel ,The use o f re in forcem ent e lem ents (e .g . dow el ,

    rockbo l trockbo l t , rock anchor & grout ) that are insta l led, rock anchor & grout ) that are insta l led

    ins ide the rock body. Th is sys temins ide the rock body. Th is sys tem stab i l isesstab i l i ses t het he

    rock by increas ing i tsrock by increas ing i ts in terna l inherent s t rengthin terna l inherent s t rength ..

    The e lement m ust be ins ta l led across a w eaknessThe e lement must be insta l led across a weak ness

    p lane. In pr inc ipa l i t i s s im i la r to t he ac t ion o fp lane. In pr inc ipa l i t i s s imi la r to t he ac t ion o f

    rebarsrebars in re in forced conc rete or prein re in forced c oncrete or pre --tens ionedtens ionedrebar in prerebar in pre --s t ressed conc rete .s t ressed concret e .

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    28/47

    When w eakness p lane that induces ins tab i l i ty canWhen w eakness p lane that induces ins tab i l i ty can

    be ident i f ied (d is t inc t ive) then, the inherentbe ident i f ied (d ist inc t i ve) then, the inherents t rength o f t h is p lane can best rength o f th is p lane can be ut i l i sedut i l i sed to ob ta into obta in

    s tab i l i t ys tab i l i t y approach is t o increase i ts shearapproach is t o increase i ts shear

    s t rength by increas ing normal s t ress on th is p lanest rength by increas ing normal s t ress on th is p lane

    Rock bo lt & dowe l a re used toRock bo l t & dowe l a re used to s tab i l i ses tab i l i se unstab leunstab le

    b locks. Bo l t must be o f su f f ic ient length so that i tb locks. Bo l t must be o f su f f ic ient length so that i t

    ex t ends wel l beyond the w eakness p lanes thusext ends wel l beyond the w eakness p lanes thus

    anchor ing the unstab le b locks t o a s t ronger rockanchor ing the unstab le b lock s to a s t ronger rock

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    29/47

    Main c om ponent s of ROCK DOWELMain c om ponent s of ROCK DOWEL

    BONDING AGENT:

    resin or groutLOCKING

    NUT

    BEARING PLATE

    REINFORCEMENT

    ELEMENT: steel rebar

    Basic des ign o f rock bo l t & dowe lBasic des ign o f rock bo l t & dowe l

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    30/47

    A rock bo l t is an ac t ive (tens ioned) dow el used forA rock bo l t is an ac t ive (tens ioned) dow el used fors tab i l i s ingstab i l i s ing rock jo in ts . Simi lar t o the use o frock jo in ts . Simi lar t o the use o f

    tensi oned rebar in pretensioned rebar in pre --s t ressed conc rete . Tens ionst ressed conc rete . Tens ion

    inducedinduced immeda i te lyimmeda i te ly dur ing ins ta l la t iondur ing ins ta l la t ion

    Insta l led rock bo lt w i thInsta l led rock bo l t w i th spher ica lspher ica l bear ing p la te &bear ing plate &

    t ensioning nut . Spher ical seat ensure eventensioni ng nut . Spher ical seat ensure even

    dis t r ibu t ion o f bo l t t ens iond is t r ibu t ion o f bo l t t ens ion

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    31/47

    Various types and surface f in ished of rebar usedVar ious types and surface f in ished of rebar used

    as for rock bo l t , mater ia l can s tee l ,as for rock bo l t , mater ia l can s tee l , f ibref ibre

    reinforc ed conc rete (FRC)reinforc ed conc ret e (FRC)

    ROCK BOLT: 25 mm Steel rebar (15 to 30 m mROCK BOLT: 25 mm Steel rebar (15 to 30 m m

    diameter ) w i t h threaded length & loc k ing nutd iameter ) w i t h threaded length & loc k ing nut

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    32/47

    Tens ion ing rock bo l t dur ing ins ta l la t ion ;Tens ion ing rock bo l t dur ing ins ta l la t ion ;

    hydraul ic jack & s t ress ing cha i rhydraul ic jack & s t ress ing cha i r

    Rockbol tRockbo l t has l im i ted t ens i le s t rength (150has l im i ted t ens i le s t rength (150 200200

    k Nk N per bol t ) and length is betw een few m t oper bo lt ) and length is betw een few m to

    about less than 12 m. Ins ta l la t ion is com plex &about less than 12 m. Insta l la t ion is com plex &

    expens ive.expens ive.

    InIn s tab i l i s ingstab i l i s ing a larger unstable b loc k (e.g. w edgea larger unstable b loc k (e.g. w edge

    of several thousandsof several thousands tonnetonne ), the num ber of bol ts) , the num ber of bol ts

    requ i red may exc eeds i tsrequ i red may exc eeds its economica l l im i teconomica l l im i t andand

    the i r e f fec t ive lengths m ay not be suf f ic ientthe i r e f fec t ive lengths m ay not be suf f ic ient

    Need for a larger s ize and higher capac i t y rockNeed for a larger s ize and higher capac i ty roc k

    re in forcement methodre in forcement method

    Opt i on is ROCK ANCHOR wit h lengt h exc eeds 20Opt ion is ROCK ANCHOR wi th l ength ex ceeds 20

    m and capac i ty few t housandsm and capac i t y few thousands tonnestonnes

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    33/47

    FullyFul ly --grouted rock anchor & anchor head;grouted rock anchor & anchor head; debondeddebondedover f ree tendon length w i th f ixed anchor pro tec t ionover f ree tendon length w i th f ixed anchor pro tec t ion

    mat er ia l is mul t ip le s t rands s tee l cab les , s imi la r tomat er ia l is mul t ip le s t rands s tee l cab les , s imi la r to

    the c ables used in suspension br idgethe c ables used in suspension br idge

    Tens ion ing o f rock anchorTens ion ing o f rock anchor

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    34/47

    Weathered s t rong rock l ike gran i te (Zone 4Weathered s t rong rock l ike gran i te (Zone 4 6) are6) are

    not su i tab le t o be re in forced us ingnot su i t ab le to be re in forced us ing rockbo l trockbo l t . In w eak. In weakrock the bonding betw een bo lt and sur rounding rockrock the bonding betw een bo l t and surround ing rock

    are w eak. Weak bonding w i l l no t produce suf f ic ientare w eak. Weak bonding w i l l no t produce suf f ic ient

    tens ion in the bo l ttens ion in the bo l t

    Minera ls ar rangement (Minera ls ar rangement (s la teys la tey && sch is tos i t ysch is tos i t y) in) in

    metam orph ic rocks m ay weaken ing these rock smetamorph ic rocks m ay w eaken ing these rocks

    (s imi lar t o(simi la r t o grannulargrannular so i l ). Re in forcement met hodso i l ). Re in forcement met hod

    l i ke rock bo l t & rock anchor a re no t recommendedl i ke rock bo l t & rock anchor a re no t recommended

    in these rocks, main ly due to w eak bondingin these rocks, main ly due to w eak bonding

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    35/47

    Use of rock bo l t as tunne l re in forcementUse o f rock bo l t as tunne l re in forcem ent

    Use o f rock bo l t asUse o f rock bo l t as s tab i l i s ingstab i l i s ing mechan ism fo rmec hanism for

    rock s loperock s lope

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    36/47

    In pr inc ip le , these three re in forcement e lem entsIn pr inc ip le , these three re in forcement e lem entsare s im i lar in design. The only d i f ferenc es areare s imi lar in design. The only d i f ferences ar e

    the i rthe i r s tab i l i sa t ionstab i l i sa t ion capac i t y , purpose andcapac i t y , purpose and

    ins ta l la t ion .ins ta l la t ion .

    They consist essent ia l ly of tendon/bar, anchorageThey consist essent ia l ly of tendon/bar, anchorage

    (bonding agent ) bear ing p la te & tens ion ing dev ice(bonding agent) bear ing plat e & t ensioning device

    Rock bo l t is more expens ive to ins ta l l than rockRock bo l t is more expens ive to ins ta l l t han rock

    dow el , they are e f fec t ive for longdow el , they are e f fec t ive for long--te rmte rm

    stab i l i sa t ionstab i l i sa t ion (c iv i l engineer ing structure) .(c iv i l eng ineer ing s t ruc t ure).

    Rock dow el is fo r shor tRock dow el is fo r shor t --te rm re in forcem ent ( forterm re in forcem ent ( for

    min ing & tem porary support in t unne l ).min ing & tem porary suppor t in tunne l ).

    They are used to inc rease the inherent s t rength o fThey are used to inc rease the inherent s t rength o fw eakness p lanes in rock e .g . shear s t rength o fw eakness p lanes in rock e .g . shear s t rength o f

    unstab le jo in tunstable jo int

    For larger unstable b loc ks (e.g. unstable b loc ksFor larger unstable b loc ks (e.g. unstabl e b lock s

    of severalof several tonnestonnes in p lane fa i lure) rock anchor isin p lane fa i lu re) rock anchor is

    recomm ended. Ins tead o f tendon rock anc horrecom mended. Ins tead o f tendon rock anc hor

    cons is ts o f h igh capac i ty m ul t ip le s t rands s tee lcons is ts o f h igh capac i ty m ul t ip le s t rands s tee l

    cables (cables used in suspension br idge)cabl es (cabl es used in suspension br idge)

    Dow el is pass ive bo l t , ins ta l led w i t hout anyDow el is pass ive bo l t , ins ta l led w i t hout any

    tension. Tension in dow el develop eventual lyt ension. Tension in dow el develop eventual l y

    a f ter there is movement in jo in ts i t in tersect .a f ter there is movement in jo in ts i t in tersect .

    Rock bo l t is ac t ive dow el , ins ta l led w i t hRock bo l t is ac t ive dow el , ins ta l led w i t hpretension (usual ly about (60pretensi on (usual ly about (60 70 % T70 % T bb ) . Due t o). Due t o

    th is preth is pre --tens ion, rock bo l t exh ib i t s severaltens ion, rock bo l t ex h ib i ts severa l

    pos i t ive character is t ics as permanentpos i t ive character is t ic s as permanent

    re in forcement .re in forcement .

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    37/47

    Rockbol tRockbo l t ins ta l led a t an ang le to the w eaknessins ta l led a t an ang le to the w eakness

    p lanes may increase i tsp lanes may increase i ts s tab i l i s ingstab i l i s ing ef fec te f fec t

    Inclined bolt

    Ttn

    th

    Sl id ing o f rough join t sur faces may lead t o d i la t ionSl id ing o f rough jo in t sur faces may lead t o d i la t ion

    (opening of jo int ) . Di lat ion(opening of jo int ) . Di lat ion induces tens ion in toinduces tens ion in to

    rock dow e lrock dowe l andand addi t iona l tens ion to rock bo l tadd i t iona l tens ion to rock bo l t ..

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    38/47

    Rock bo l t in tersect ing rough c lean jo in t : d i la t ionRock bo l t in t ersect ing rough c lean jo in t : d i la t ion

    leads to an inc rease in bo l t t ens ion (pos i t iveleads to an inc rease in bo l t t ens ion (pos i t ive

    e f fec t )e f fec t )

    Rock bo l t in tersect ing f i l led join t : no d i la t ion dueRock bo l t in t ersect ing f i l led jo in t : no di la t ion due

    to c ompress ib i l i ty o f in f i l l , th is leads to eventua lto c ompress ib i l i ty o f in f i l l , th is leads to eventua l

    loss (creep) in bol t tension (negat ive ef fec t)loss (creep) in bol t tension (negat ive ef fect )

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    39/47

    Roof sect ion is the most c r i t i c a l par t o f a tunne l .Roof sect ion is the most c r i t i c a l par t o f a tunne l.Rock bo l t o f d i f fe rent lengths are used toRock bo l t o f d i f fe rent lengths are used to

    re in forced h igh ly jo in ted/f rac t ured roof sect ionre in forced h igh ly jo in ted/f rac t ured roof sect ion

    (reduce roof fa i lu re rock fa l l & w edge fa i lu re)( reduce roof fa i lu re rock fa l l & w edge fa i lure)

    Excavation of rectangular tunnel in horizontally bedded sedimentExcavation of rectangular tunnel in horizontally bedded sedimentaryaryrock may induce a phenomenon calledrock may induce a phenomenon called bed separationbed separation at the tunnelat the tunnel

    roof. If the lower bed is thinner this leads to a larger deflectroof. If the lower bed is thinner this leads to a larger deflectionion (as(as

    1/h1/h33). When the lower bed deflects more downwards, it will be). When the lower bed deflects more downwards, it will be

    separated from the upper bed creatingseparated from the upper bed creating aa gapgap between the bedsbetween the beds

    Bedded strata h2 = 2.4m

    Rectangular-

    shaped tunnel

    w = 12m

    h1 = 1.2m

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    40/47

    Bed separationBed separation can be reduced by installing rock bolts at the roofcan be reduced by installing rock bolts at the roof

    tunnel. When the lower & upper beds are bolted together they fortunnel. When the lower & upper beds are bolted together they formm

    aa composite beamcomposite beam (beam(beam setarasetara), the resulting bed is thicker (thus), the resulting bed is thicker (thus

    smallersmaller )) and higher shear strength at the bedding plane.and higher shear strength at the bedding plane.

    Rock boltsh2

    h1

    Stab i l i ty & dra inage are the m ain prob lems w i thStab i l i ty & dra inage are the m ain prob lems w i th

    s lope exc avated in sch is t & s la te (met amorph ics lope exc avated in sch is t & s la te (met amorph ic

    rock s). Even w i th gent le & low ang le prof i le (2 mrock s). Even w i th gent le & low ang le prof i le (2 m

    height w i th bench ing) the s lope remains unstab lehe ight w i th bench ing) the s lope remains unstab le

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    41/47

    Rock s lopes can fa i l in var ious modes & eachRock s lopes can fa i l in var ious modes & each

    method o fmet hod o f s tab i l i sa t ionstab i l i sa t ion is only sui t able/ef fec t i veis only sui table/ef fect ivefor spec i f ic m ode o ffor spec i f ic m ode o f unstab i l i tyunstab i l i ty ..

    Usua l ly more than one met hods are requ i red toUsual ly more t han one methods are requ i red to

    s tab i l i ses tab i l i se a rock s lope.a rock s lope.

    Comm only used method are :Comm only used method are : rockbo l trockbo l t ++ w i remeshwi remesh

    ++ sho tc re tesho tc re te . Long. Long --te rm e f fec t due to w ea thering i ste rm e f fec t due to w ea ther ing is

    reduced byreduced by min imis ingmin imis ing the presence o fthe presence o f

    w eather ing agents t hrough dra inage sys tem:w eather ing agents t hrough dra inage sys tem:

    sur face drainage & w eepsur face drainage & w eep--holes.holes.

    Sprayed concret e / Sprayed concret e / sho tc re tesho tc re te (spec ia l cement m ix(spec ia l cement m ix

    of 20of 20 --30mm th ic k) app l ied on the s lope face he lps30mm th ic k) app l ied on the s lope face he lps

    to reduceto reduce w eather ing agentw eather ing agent f rom seeping into t hef rom seeping into t he

    slope (Chemi cal w eather ing in Chap 6.0).s lope (Chemic al w eather ing in Chap 6.0) .

    I t i s a normal prac t ic e to sprayI t is a normal prac t ic e to spray sho tc re tesho tc re te on s lopeon s lope

    face w h ich has been p rotec t ed w i t hface w h ich has been p rotec t ed w i t h w i remeshwi remesh ,,

    th is is main ly due to :th is is main ly due to :

    Bo th methods comp l iment w i th each o therBo th methods comp l iment w i th each o ther

    a l though each m ethod de l ivers d i f fe renta l though each m ethod de l ivers d i f fe rent

    mec hanisms ofmec hanisms of s tab i l i sa t ionstab i l i sa t ion ..

    Thin layer ofThin layer of sho tc re tesho tc re te is w eak and exh ibi t s low eris w eak and exh ib i t s lower

    s t i f fness,s t i f fness, w i remeshwi remesh can ac t ascan ac t as re in forcementre in forcement forfor

    th is layer o fth is layer o f sho tc re tesho tc re te . By cover ing t he. By cover ing t he w i remeshwi remesh

    (s tee l ) w i th layer o f(s tee l ) w i t h layer o f sho tc re tesho tc re te prov ide pro tec t ionprov ide pro tec t ionagains t co r ros ion (con tac t w i th w a te r & Oagainst c o r ros ion (con tac t w i th w a te r & O22 ))

    Th is procedure ensures both m ethods to func t ionThis procedure ensures both m ethods to funct ion

    ef fec t ive ly for a long per iod o f t imeef fec t ive ly for a long per iod o f t ime

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    42/47

    Maintenance cost s on s lope &Main tenance cost s on s lope & stab i l i sa t ionstab i l i sa t ion

    met hods (a f ter const ruc t ion) can be cost ly .met hods (a f ter const ruc t ion) can be cost ly .

    Se lec t ion o f appropr iate & e f fec t ive m ethod, &Selec t ion o f appropr ia te & e f fec t ive m ethod, &cor rec t ins ta l la t ion procedures ensurecor rec t ins ta l la t ion procedures ensure

    stab i l i sa t ionstab i l i sa t ion met hods are funct ion ing e f fec t ive lymet hods are funct ion ing e f fec t ive ly

    for the required safet y level and durat ion .for the required safety level and durat ion .

    Rockbo l tRockbo l t is a met hod recomm ended for longis a met hod recomm ended for long--

    te rmte rm stab i l i sa t ionstab i l i sa t ion how ever , i ts e f fec t ivenesshow ever , i ts e f fec t iveness

    great ly depending on how i t i s ins ta l led e .g .great ly depending on how i t i s ins ta l led e .g .

    borehole s ize, t ension level & t ensioning deviceborehole s ize, tension level & tensioni ng device

    (bear ing p la te & nut .(bear ing pla te & nut .

    F igure 11.3 exhib i ts several m ethods forFigure 11.3 exhib i t s several met hods for

    s tab i l i s ingstab i l i s ing rock s lope o f d i f ferent sur facerock s lope o f d i f fe rent sur face

    condi t ions.cond i t ions.Table 11.1 Exam ples ofTable 11.1 Exam ples of s tab i l i sa t ionstab i l i sa t ion methodsmethods

    for s lope & tunne l in rock m ass.for s lope & tunne l in rock m ass.

    Table 11.1: Methods ofTable 11.1: Met hods of s tab i l i sa t ionstab i l i sa t ion for c iv i lfo r c iv i l

    eng ineer ing s t ruc t ures and min ing ac t iv i t ies (a f tereng ineer ing s t ruc t ures and min ing ac t iv i t ies (a f ter

    Stacey & Page, 1986)St acey & Page, 1986)

    Grouted rock bolt + wire mesh + shotcrete. Structures excavated in rock mass e.g. road

    tunnel and service tunnel in mining.

    Grouted bolt + wire mesh + shotcrete +

    suitable drainage system (surface drainage

    & weep holes).

    Excavation of slope for highways and building

    structures.

    Yielding steel arches + concrete slabs +

    water-proof lining + shotcrete + rock anchor

    + grouted rock bolt.

    Permanent underground excavations e.g. h.e.p.

    cavern house, mining service tunnel & sport

    complex.

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    43/47

    Plane failurePlane failure is usually associated with ais usually associated with a large unstable blocklarge unstable block

    that tends to slide along a weakness plane (e.g. bedding or faulthat tends to slide along a weakness plane (e.g. bedding or faultt

    planes).planes). ReinforcingReinforcing the unstable block to a more stable rockthe unstable block to a more stable rock

    mass is highly recommended, using rock bolts and rock anchor.mass is highly recommended, using rock bolts and rock anchor.

    Wedge failureWedge failure is associated with unstable medium to large sizeis associated with unstable medium to large size

    block that tends to slide along intersecting weakness planesblock that tends to slide along intersecting weakness planes

    (joints or faults). Similar to plane failure,(joints or faults). Similar to plane failure, reinforcingreinforcing the unstablethe unstable

    block to a more stable rock mass is recommended using rockblock to a more stable rock mass is recommended using rock

    bolts (for medium block) or rock anchor (for large blocks).bolts (for medium block) or rock anchor (for large blocks).

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    44/47

    Toppling or rocks fallToppling or rocks fall is associated with smaller size blocks. Failureis associated with smaller size blocks. Failure

    is not alongis not along distinctive sliding planesdistinctive sliding planes. The unstable rocks are blocks. The unstable rocks are blocks

    that have been separated from the main rock body by intersectingthat have been separated from the main rock body by intersecting

    joints (> 3 sets). Water can penetrate the slope easily due to mjoints (> 3 sets). Water can penetrate the slope easily due to manyany

    joint sets.joint sets. ReinforcementReinforcement alone is not suitable for this type ofalone is not suitable for this type of

    unstabilityunstability.. Support systemSupport system like wirelike wire--mesh &mesh & shotcreteshotcrete together withtogether with

    rock bolts are recommended.rock bolts are recommended.

    Flexural topplingFlexural toppling isis unstabilityunstability due to rock blocks that are separateddue to rock blocks that are separatedby at least one set of near vertical joints or bedding planes. Fby at least one set of near vertical joints or bedding planes. Failure isailure is

    associated with sliding plane. The slender (thin) vertical rockassociated with sliding plane. The slender (thin) vertical rockblocksblocks

    can be made stronger bycan be made stronger by bonding them togetherbonding them together (composite beams)(composite beams)

    using rock bolts (thinner blocks) or rock anchor (thicker blocksusing rock bolts (thinner blocks) or rock anchor (thicker blocks))

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    45/47

    Drainage system (method ofDrainage system (method of stabilisationstabilisation) is an essential measure) is an essential measure

    for rock slopes excavated in tropical countries (high annualfor rock slopes excavated in tropical countries (high annual

    rainfall). The drain also acts as buffer zone for any fallen rocrainfall). The drain also acts as buffer zone for any fallen rockk

    Drainage system (method ofDrainage system (method of stabilisationstabilisation) at the crest of) at the crest of

    protected slopeprotected slope

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    46/47

    Methods o fMethods o f s tab i l i sa t ionstab i l i sa t ion for rock s lopefor rock s lope

    Comprehensive drainage system (surface & internal drainage]Comprehensive drainage system (surface & internal drainage]

    for large size slopes and where water is a critical factor.for large size slopes and where water is a critical factor.

  • 7/31/2019 Chp 11 (Rock Stabilisation)

    47/47


Recommended