rock anchoring

7/24/2019 Rock Anchoring

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1.INTRODUCTION:

A rock anchor or rock bolt is a long anchor bolt, for stabilizing rock excaations, !hich

"a# be $se% in t$nnels or rock c$ts. It transfers loa% fro" the $nstable exterior, to the

confine% &an% "$ch stronger' interior of the rock "ass.

Rock bolts !ere first $se% in "ining starting in the 1()*s, !ith s#ste"atic $se

%oc$"ente% at the +t ose-h ea% /ine in the U+ in the 1)0*s.

The Rock Anchoring is a atente% efficient an% econo"ical sol$tion for the installation of

Anchors in Rock an%2or an# +oli% /e%ia. The +#ste" is 3cologicall# so$n% as it re4$iresno excaation or re"oal of s-oils an% has no ibration, ha""ering or ex-losie

re4$ire"ents in its installation. No bon%ing agent re4$ire% in the installation -rocess as

the +#ste" Co"-onents, $-on their -lace"ent, %irectl# transfers the a--lie% %esignforces %irectl# into the s$rro$n%ing "e%ia.

The +#ste" can be %esigne% an% installe% to han%le an# intensit# an% t#-e of loa%ing

-lace% $-on it an% is onl# li"ite% b# the strength of the s$rro$n%ing "e%ia itself. It iseasil# installe% !ith a "ini"$" a"o$nt of ti"e, labor an% e4$i-"ent. Once installe%, the

+#ste" can be easil# teste% to its %esign2$lti"ate loa% bearing ca-acit# an% is rea%# for

i""e%iate $se !ith kno!n installe% str$ct$ral integrit#. No %r#ing an%2or c$ring ti"ere4$ire%.

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0.AICATION+

5ro$n% anchors are $se% in ciil engineering for the follo!ing a--lications:

o To resist lateral thr$st on retaining !alls an% in-situ diaphragm !alls,

o 6or stabilizing of slo-es an% lan% sli%es,

o To resist $-lift on base"ents an% other fo$n%ations,

o To strengthen "asonr# an% concrete %a"s, an%

o 6or testing of large %ia"eter -iles.

Rock anchoring has its a--lication $se% -rofitabl# in follo!ing areas of ciil engineering7

Retaining !alls

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To!er bases

Concrete str$ct$res

Concrete for" har%!are

T$nnels

/ines

Da"s

8ri%ges

+lo-e stabilization

Rock fall -rotection

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=.T3R/INOO5

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6or the -$r-ose of this stan%ar% the follo!ing %efinitions shall a--l# &see 6ig. 1 '.

er"anent Anchors7 An# anchor re4$ire% an% constr$cte% for serice life of thestr$ct$re.

Te"-orar# Anchors 7 An# anchor re4$ire% an% constr$cte% for %$ration ofconstr$ction -erio% onl#.

6ixe% ength7 The length of the anchor !hich is gro$te% in, fro" !hich the -$llo$tca-acit# of anchor is achiee%.

6ree ength7 The -art of the anchor !hich is not bon%e% to the s$rro$n%ing area an%is free to elongate.

6ixe% ength 5ro$t7 Ce"ent gro$t !hich is -lace%2in>ecte% in the fixe% length ofthe anchor that -roi%e% anchorage.

6ree ength 5ro$t7 The gro$t s$rro$n%ing the free length of the anchor. Thissecon%ar# in>ection is -roi%e% s$rro$n%ing the sheathing in case of sheathe% anchors.

6or $nsheathe% anchors, this gro$t is -roi%e% after the stressing is co"-lete% an% anchor

is locke%. The "ain -$r-ose of this gro$t is to -roi%e corrosion -rotection.

Consoli%ation 5ro$ting75ro$ting exec$te% in the area s$rro$n%ing the hole -riorto inserting cables either to !ater-roof the hole or to strengthen the rock.

Design oa%7 Assigne% loa% on anchor after allo!ance for all losses.

restressing +teel7 The ele"ent of the anchor !hich is allo!e% to elongate an% isanchore% at the botto" to %eelo- necessar# -restressing force. This steel can be high

tensile -lain !ires or stan%ar% cables.

+heathing7 3nclos$re to the -restressing steel -roi%e% for corrosion -rotection.Anchorage 7 The "eans b# !hich -restressing force is trans"itte% to rock or str$ct$ral

ele"ent.

8earing late7A -late $se% at the to- en% of the -restresse% anchor to %istrib$teanchor force to the str$ct$re.

Allo!able 8on% +tress of Rock7 8on% stress bet!een the rock an% the gro$t$se% in the %esign.. This nor"all# ass$res a "ini"$" safet# factor of 9.

$geon7 $geon is %efine% as flo! of !ater in litres2"in$tes2"etre

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length of the test section at a -ress$re of l/N2"e & 1* kgf2c"0 ' %$ring !ater test.

restressing 6orce7 The loa% to !hich the anchors are initiall# stresse% to cater for%esign loa% an% allo!ance for the ex-ecte% losses.

?. N3C3++AR DATA

+erice life of anchor &te"-orar# or -er"anent'@

Design loa% -er anchor@ an%

+oil inestigation for follo!ing factors:

Co"-lete borehole log in%icating t#-es of soil an% rock enco$ntere% !ith res-ect to

%e-th. The %e-th of -enetration into rock !ith core %rilling sho$l% be "ini"$" 1* " Un %raine% shear strength an% b$lk %ensit# at %ifferent %e-ths

iii'+hear strength an% $nit !eight of rock

+$l-hate an% chlori%e contents in soil as !ell as gro$n% !ater

er"eabilit# of rock an% fiss$rs 7-erio$s zones !ater table an% artesian hea% if an#

recor%e% on boreholes

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col$"n, is lo!ere% into the hole. The s-rea%ing2s-inner a--arat$s is attache% an%

centere% in contact !ith the s$rface. The +#ste" is rotate% $sing the hole %rilling -o!er

$nit, o-ening the anchor hea% into the loa% bearing "e%ia, in a -re%eter"ine% controlle%"anner. This -laces the anchor hea% conicall# into the rock, !hich effectiel# $tilizes the

"axi"$" strength of the loa% bearing rock ia the Anchoring +#ste". The s-rea%ing

col$"n is re"oe% allo!ing the +#ste" to be i""e%iatel# teste% an% -lace% into its%esigne% $se. If re4$ire%, the +#ste" "a# be -ost7tensione% in or%er to "eet c$rrent

seis"ic loa%ing safet# "eas$res. Corrosion -rotection for the bars can be acco"-lishe%

ia an# %esire% "etho%s c$rrentl# $se%. The force trans"itting Anchor hea% can be "a%eof stainless steel, !hich can han%le an# co"-ressie force that is -lace on it. The bar is

the onl# co"-onent of the +#ste" that ex-eriences the tensile forces -lace% $-on the

+#ste", !hich can also be "a%e of stainless steel.

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Drilling Thro$gh Oerb$r%en7 Drilling thro$gh oerb$r%en is nor"all# carrie%o$t b# s$itable e4$i-"ent. 6or kee-ing the si%e stable, either te"-orar# easing is

-roi%e% or bentonite "$% circ$lation is $se%. The size of the hole %e-en%s $-on the

ca-acit# of the anchor. In case of incline% bores $se of casing t$be shall be obligator#.

Drilling Thro$gh Rock7 Drilling thro$gh rock is carrie% o$t b# $sing either rotar#"etho% !ith !ater fl$sh or $sing -ne$"atic -erc$ssion "etho% !ith air an%2or !ater

fl$sh.

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+$itable g$i%e s#ste" an% te"-orar# fixing of the anchor is re4$ire% to aoi% "oe"ent

of anchor %$ring gro$ting.

5ro$t t$bes are checke% to ens$re that the# are free.

+$itable s-acers are also -roi%e% !hen re4$ire% to ens$re that anchor asse"bl# %oes notget entangle%.

.? 6IG3D 3N5T< 5ROUTIN5

After the anchor is lo!ere%, the fixe% length of the anchor is gro$te%.

5ro$ting is carrie% o$t $n%er -ress$re &H =7( kg2c" 0' b# fixing a -acker at the to- of the

fixe% length or as necessar# in accor%ance !ith the t#-e of anchor.

Nor"all# thickest -ossible gro$ting &*.? !ater ce"ent ratio' is a%o-te% for -ri"ar#

gro$ting.

A%e4$ate care is re4$ire% so that the free length of the anchor re"ains free to elongate.

. +TR3++IN5

+tressing is carrie% o$t after 01 %a#s of gro$ting !hen, it attains the re4$ire% strength.

De-en%ing on the %ifferent t#-es of anchors $se%, %etails of the stressing >ack ar#.

The anchor is stresse% for abo$t 1* -ercent of the loa% an% elongation "eas$re"ents

taken be#on% this range.

This takes care of an# seating errors.

Anchor is s$bse4$entl# stresse% to 1* -ercent excess loa% oer the %esign an% elongation

note%.

After noting the elongation, the anchor is locke% either to %esign loa% or -art of the%esign loa% %e-en%ing on the re4$ire"ents.

(. +AC3R+ B C3NTRAI3R+

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+-acers: The -$r-ose of a s-acer is to hel- ins$re that gro$t s$rro$n%s each stran% forcorrosion -rotection an% for bon% strength %eelo-"ent. Designers sho$l% s-ecif# the

%esire% %istance bet!een s-acers &t#-icall# J71*J'.

Centralizers: Centralizers are -lace% oer the asse"ble% stran% b$n%le in or%er to

"aintain the re4$ire% s-acing bet!een the anchor an% the borehole so that an a%e4$ate

thickness of gro$t &"ini"$" *.?K' s$rro$n%s the anchor. A !i%e ariet# of centralizers

are aailable %e-en%ing $-on the anchor t#-e.

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10.R363R3NC3+

1.Hong-Yuan Fu; et alrofessor, Changsha Uni. of +cience an% Technolog#, Changsha,


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ROCK ANCHORING TECHNIQUE

SUBMITTED BY PRASANJIT ROYREGISTRATION NO- 15-21-409

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CONTENTS

TOPIC PAGE

NO.

1.INTRODUCTION.....................................................................................1

0.AICATION+..................................................................................0

9.TICA D3TAI+ O6R3+TR3++3D ROC; ANC


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10.R363R3NC3+......................................................................................11

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rock anchoring

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