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A case history of tunnelling through difficult ground

A case history of tunnelling through difficult ground
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  A Case History of Tunnelling Through Difficult Ground   R. K. Goel 1 , Anil Swarup 1 Central Mining Research Institute Regional Centre, CBRI Campus, Roorkee, India ABSTRACT dhampur!Katra section is the "irst leg o" dhampur!Srinagar!Baramulla Rail #ink pro$ect. %his section is &'km long and in(ol(es construction o" ) tunnels. %he *.11 km long +!shaped %unnel o. 1, discussed in the paper, has e-ca(ation width o" aout /.'m and height appro-imatel0 .&m. %he  primar0 supports, generall0, are steel ris with (ar0ing spacing depending upon the rock t0pe.%he main rock t0pes encountered along the tunnel alignment were sandstones, cla0 stones, silt stones and o(erurden comprising o" oulders2peles in sand02silt0 matri-. +ue to presence o" swelling minerals and weak rock "ormation with high rock co(er 3up to *1*m4, the tunnelling has e-perienced oth swelling and s5uee6ing ground conditions and the steel ri supports ha(e uckled "rom the sides. 7loor hea(ing has also een oser(ed "re5uentl0. %unnel instrumentation was carried out to stud0 the rock and support eha(iour. Simultaneousl0, the rock mass classi"ication approach was also used to stud0 the degree o" s5uee6ing and "or estimating the support pressure and design o" supports. A "le-ile s0stem o" support was adopted with success. 1. INTRODCTION dhampur!Katra section is the "irst leg o" prestigious and challenging dhampur!Srinagar!Baramulla Rail #ink pro$ect co(ering a total length o" &).8 km in the hill0 terrain o" 9ammu : Kashmir state o" India. %he pro$ect en(isages construction o" a new single line road gauge railwa0 with ma-imum speed potential o" 188km2hr with ruling gradient limited to 1 in 188.%he dhampur!Katra section is &'km long and it in(ol(es construction o" ) tunnels, aggregating to total length o" 18 km. ;ut o" ) tunnels, & are more than & km long (i6. %unnel o. 1 3*.11 km4 and %unnel o. * 3&.' km4. %he %unnel o. 1 has een e-ca(ated through $ointed and sheared cla0stone and silt stone. %he tunnelling has e-perienced oth the swelling and s5uee6ing prolems. At some locations, ecause o" high pressures, the steel ri supports ha(e de"ormed and "loor hea(ing has also een oser(ed.Central Mining Research Institute 3CMRI4 Regional Centre, Roorkee had carried out instrumentation to e(aluate and design the supports in %unnel o. 1. %he results o" tunnel monitoring together with the support design are presented as "ollows. !. SA"I#NT $#ATR#S O$ TH# TNN#" %he %unnel o. 1 has the "ollowing "eatures<Shape<+!Shape=-ca(ated >idth</.'m=-ca(ated (ertical legs<App. '.8mGradient o" tunnel<1 in 188 1  #ength o" tunnel<*118mSupports<+oule ri in weak rocks? ;uter ri IS@B 1'8  '88mm c2c 2 )'8mmc2c : inner ri IS@B 1'8 1888 c2c? Arch support resting on wall eam o" IS@B &882IS@B 1'8? #aggings o" RCC slas? ack"ill  0 M18 concrete : "illing etween ris 0 M!&8 concrete.%he ground pro"ile ao(e the tunnel is shown in 7ig. 1, which gi(es an idea o" ma-imum o(erurden o" aout *1* m around Chainage 3Ch.4 *&'8m in the tunnel. 7igure 1. #ongitudinal Section o" %unnel 1 "rom Ch. &18 to '*&8 3;tained 7rom ro$ect4%he tunnel construction was started "rom the two ends, called the dhampur endD and the Katra endD. %he e-ca(ation work was carried out 0 con(entional drill and last using heading and enching method. %. TH# G#O"OG& %he tunnels in dhampur!Katra section "all in Shiwalik Group and leistocene to recent deposits. %he tunnels tra(ersed through unconsolidated or poorl0 consolidated sediments with rocks o" upper2middle2lower Shiwalik and Murree "ormations. %he main rock t0pes encountered along the tunnel alignment eing thickl0 edded, moderatel0 so"t, sparsel0 $ointed sandstones, sheared cla0 stones and silt stones. At places the tunnel also pass through unconsolidated o(erurden material consisting o" oulders, coles and peles at oth ends coupled with high water tale. %he region is in the (icinit0 o" a ma$or structural "eature, i.e. Murree %hrust. %hus, geologicall0 a considerale length o" the tunnel passed through e-tremel0 poor tunnelling media.%he cla0 mineral anal0sis carried out 0 CMRI at Institute Instrumentation Centre, II% Roorkee shows that the cla0stone o" %unnel 1 has montmorillonite, kaolinite and illite minerals. %hese cla0 minerals ha(e swelling characteristics. '. GROND CONDITIONS AND S((ORT (R#SSR#S %he cla0 stone has een classi"ied using the E!s0stem o" Barton et al. 31F)4. Eualitati(el0 the cla0stone is descried as sheared and highl0 $ointed with three $oint sets and random $oints? $oints are closel0 spaced and the walls o" $oints are slickensided, undulating and smooth? altered $oint walls ha(ing coating o" gouge material. %he rock at the time o" e-ca(ation is generall0 dr0 ut with passage o" time ecomes moist. 7or practical purposes, silt stone can also e grouped in the same class o" cla0 stone. Accordingl0, the rating o" (arious parameters o" E!s0stem and (alue o" E "or cla0 stones is worked out 3%ale 14. %he (alue o" rock mass numer  3de"ined as the stress "ree E, i.e. E with SR7 H 14 has also een gi(en in %ale 1. &  %ale 1. Rock mass 5ualit0 E and rock mass numer  "or cla0 stoneRock %0peRE+9n9r9a9wSR7ECla0stone18!1'1&1.'!& 18.*1&'!8./&' 38.4'!188.8*1&!8.1&' 38.8/&4  - log average value4.1 Estimation of ground conditions %he in"ormation on the ground condition is re5uired "or selection o" e-ca(ation method and designing the support   s0stem "or underground openings.  on!s5uee6ing and s5uee6ing ground conditions ha(e een predicted 0 using "ollowing e5uation  proposed 0 Goel et al. 31FF'4 wherein e""ect o" tunnel si6e has also een considered<@ H 3&)'  8.** 4 B !8.1 metres314>here @ is tunnel depth or o(erurden in metres,  is rock mass numer 3stress "ree E, i.e E with SR7 H14, and B is tunnel span or diameter in metres.=5uation 1 implies that "or a s5uee6ing ground condition to occur, @ J 3&)'. 8.** 4B !8.1 metres and "or a non!s5uee6ing ground condition, @ K 3&)'  8.** 4 B !8.1  metres. 7or rock mass numer  H 8. and e-ca(ated tunnel span B H /.'m, "rom =5. 1 the minimum depth "or s5uee6ing to occur is 1)8m. Accordingl0, the tunnel depths "or (arious degree o" s5uee6ing are shown in %ale &. %ale &. rediction o" degree o" s5uee6ing using  3Goel et al., 1FF'4S.  o.+egree o" S5uee6ingCorrelations "or redicting +egree o" S5uee6ingCritical %unnel depth @ "or  H8. and B H /.'m1.Mild s5uee6ing3u a 2a H1!*L4&)' 8.** .B !8.1 K@K'8 8.** .B !8.1 and 9 r   29 a  K8.'1)8 K @ K&818m 0 Singh et al.&.Moderate s5uee6ing3u a 2a H*!'L4'8 8.** .B !8.1 K@K /*8 8.** .B !8.1 and 9 r   29 a  K8.'&8 K @ K *F'*.@igh s5uee6ing3u a 2a J 'L4@J/*8 8.** .B !8.1 and 9 r   29 a  K8.&'*F' K @  Notation: N = Rock mass number (Q wit !R"=1#$ % = &unnel widt in metres$ ' = &unnel det in metres$ u a  = radial tunnel deformation) a = tunnel radius in metres) *  r   = %arton+s ,oint rougness number  *  a  = %arton+s ,oint alteration number  %he ma-imum tunnel depth is *1*m at Ch. *&'8m 37ig. 14 and there"ore the moderate s5uee6ing ground condition was anticpated 3%ale &4. Assuming the same rock mass numer  (alues all along the tunnel and using 7ig. 1 "or the estimation o" tunnel depth, degree o" s5uee6ing along the tunnel has  een estimated as "ollows< •  ild !/uee0ing (&unnel et 142 to 32m#- Ch. &)18 to &F/'m? **18 to *8m : */'8 to &'m 3%otal length 1&88m4 •  oderate !/u. (&unnel et 32 to 567m#- Ch. &F/' to **18m : *8 to */'8m 3%otal length '1'm4   It ma0 e noted here that the ao(e estimation has almost matched with the actual site oser(ations. *  4.3 Estimation of roof su((ort (ressure %he correlation o" Goel et al. 31FF'4 has een used to estimate the support pressures in s5uee6ing ground condition. %he estimated support pressure "or (arious tunnel depths are shown in %ale *.%ale *. =stimated support pressure (aluesS.o.%unnel +epth, mSupport Bressure, MBa11'88.1*'&&888.'*1*&'88./)'*888.&%he ao(e support pressure (alues 3%ale *4 are otained a"ter taking into consideration the correction "actor "or tunnel closure as suggested 0 Goel et al. 31FF'4 a"ter allowing the tunnel to de"orm to appro-imatel0  per cent o" its si6e. In case the supports are not "le-ile, the support pressure (alues shall e higher than what has een shown in %ale *. ;n the asis o" ao(e empirical approach, the steel ri support o" ma-imum capacit0 8. MBa with loose muck ack"ill which can allow 1'!&8 cm 3*! L o" tunnel si6e4 o" controlled radial rock de"ormation has een suggested to use as primar0 support. Idea ehind this was that the loose ack"ill will asor the rock de"ormations and shall reduce the load on the steel ris. Accordingl0, the steel ri supports with loose muck ack"ill ha(e een installed in the tunnel and the support eha(iour has een monitored 0 installing the load cells and the closure points. Suse5uentl0, on the asis o" monitoring results, the support design has een recommended. ). *ONITORING O$ ROC+ AND S((ORT B#HA,IOR  +e(elopment o" rock load on steel ris and ri de"ormation were monitored. %he load cells and the closure points "or measuring de"ormation are installed as shown in 7ig. &. 7igure * shows the position o" "ace and ench at the time o" installation o" instruments on +ecemer 1*, &88*.7igure &. Section showing position o" load cells and the closure studs, Ch. */8 : */1m, dhampur =nd7igure *. #!section showing position o" instrumented section with heading and  enching "aces, dhampur =nd   %he data o" the two load cells installed at Ch. *G/1m is plotted against time and shown in 7ig. G. %he ri de"ormation2closure at Ch. *G/1m and the "ace : ench ad(ance is also shown in 7ig. G. %he trend o" load and de"ormation in oth the ris was almost same. %here"ore onl0 the "igure o" load and de"ormation at Ch. *G/1 are shown. =-ca(ation work o" "ace and ench was continuousl0 going on a"ter installation o" instruments. 7igure G shows that there is almost no de(elopment o" load up to &8 da0s. %he "ace ad(ance e""ect was not shown 0 the load cells "or &8 da0s. %his is proal0 ecause the wall eam has also mo(ed under the in"luence o" ench e-ca(ation and thus the wall eam could not pro(ide the desirale reaction. @ence, the stailit0 o" wall eam must e ensured in heading and enching method o" tunnelling.%he de(elopment o" load started a"ter &8 da0s. Initiall0 the rate o" load de(elopment was high ut with time it has reduced. A"ter aout 1G8 da0s o" oser(ations, the rate o" load de(elopment has almost staili6ed 37ig. G4. %he load shown 0 the le"t and right load cells is around '% and )8% respecti(el0. Considering the inner span o" steel ri as '.'8m and ri spacing as 1.8m, the support  pressure works out "rom the load is etween &.* to &.' kg2cm &  38.&* to 8.&'Ma47igure G also shows the plot etween time a"ter +ecemer 1*, &88* and the de"ormation or closure. Initiall0 the de"ormations were insigni"icant, ut a"ter 18 da0s it increases and continues to increase graduall0 till the last oser(ation 37ig. G4. %he ma-imum de"ormation is aout &'cm in aout 1'8 da0s, which is aout G.'L o" tunnel si6e 3inner tunnel width '.'m4. %he increase in load and de"ormation is remains continued e(en when the "ace was aout F8m awa0 "rom the instrumented section, i.e. aout 1'+. Load Observations (Electrical) in T1 (Udhampur) at Chainage 3461m -40-20020406080100120140160180020406080100120140160 Time in No. of Days after December 13, 2003 Left Load Cell, Tonnesi!"t Load Cell, Tonnes#eadin!, m$enc"in!, mClos%re, cm 7igure G. %ime (s. load, closure, "ace ad(ance and ench ad(ance, Ch. *G/1, dhampur =nd%he monitoring o" re(ised support s0stem shows that the supports are working satis"actoril0. Accordingl0, the "ollowing "le-ile support s0stem has een recommended. -. TH# $"#IB"# S((ORT S&ST#* %he primar0 "le-ile support s0stem comprises o" &8cm thick muck ack"ill etween the ri o" IS@B 1'8 and the e-ca(ated rock peripher0 to allow controlled rock de"ormation. In case o" (er0 small much pieces, it was suggested that some other compressile material shall e "illed so that 1'!&8cm total de"ormation can e asored. %he support monitoring has also een recommended to start immediatel0 at "re5uent inter(als along the tunnel length. '
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