Tun­nelling Through the Ages

NBM&CW - - CONTENTS -

His­tory has seen the evo­lu­tion of tun­nelling start­ing with cave for­ma­tion, for water man­age­ment, un­der­ground trans­porta­tion, min­eral ex­trac­tion and for war­fare pur­poses. The old­est ref­er­ence of a tun­nel was in Per­sia where tun­nels were built to con­nect wells called ‘qanats’ that pro­vided a re­li­able sup­ply of water in hot, arid and semi­arid cli­mates. The deep­est known qanat is in the Ira­nian city of Gon­abad, which af­ter 2,700 years, still pro­vides water for drink­ing and agri­cul­ture pur­poses to nearly 40,000 peo­ple.

Ini­tially, crude tools like chis­els, ham­mers, spades and shov­els, were used. But with in­creas­ing mod­ern­iza­tion, the civil engi­neer­ing tun­nelling tech­nol­ogy has pro­gressed by leaps and bounds. This is be­ing re­al­ized through ad­vance­ments in ge­o­log­i­cal and hy­dro-ge­o­log­i­cal engi­neer­ing, tun­nel de­sign, ca­pac­ity, con­struc­tion meth­ods, speed and maintenance dur­ing op­er­a­tions, and safety dur­ing con­struc­tion and op­er­a­tions get­ting in­te­grated in all as­pects.

His­tor­i­cal evo­lu­tion of tun­nelling

In civil engi­neer­ing ap­pli­ca­tion for tun­nels, the need for rev­enue gen­er­a­tion and meet­ing the ob­jec­tives has led to man­i­fold changes in tun­nelling, but some fun­da­men­tals still re­main un­changed. For ex­am­ple, the cut-and-cover method (that in­volves dig­ging a deep trench, con­struct­ing a roof at an ap­pro­pri­ate height and cov­er­ing the trench) has its first re­ported use in 2000 BC in Baby­lon and is still em­ployed in mod­ern-day con­struc­tion.

Ge­ol­ogy is the most im­por­tant fac­tor that de­ter­mines the na­ture, form and cost of any tun­nel. Ow­ing to the un­cer­tain ge­ol­ogy, tun­nelling presents a risky un­der­tak­ing pri­mar­ily be­cause of the ge­o­log­i­cal com­plex­ity en­coun­tered, and also be­cause of the lack of com­men­su­rate knowl­edge, skill and ex­pe­ri­ence.

Although, the ba­sic prin­ci­ples of geotech­ni­cal and ge­o­log­i­cal engi­neer­ing have re­mained the same, the ap­pli­ca­tion of in­ter­dis­ci­pli­nary sci­ences, evo­lu­tion of an­a­lyt­i­cal tools, re­fine­ment in in­stru­men­ta­tion and com­pu­ta­tional meth­ods over the past 25 - 30 years have im­proved our abil­ity to bet­ter un­der­stand the in-situ con­di­tions, and hence, tun­nel de­signs.

The ex­plo­sives tech­nol­ogy has un­der­gone sig­nif­i­cant ad­vance­ments. What started with the use of gun pow­der as an ex­plo­sive in the first mech­a­nized tun­nel con­struc­tion (the drill and blast method) in France in 1681, tran­sited to the use of Nitro­glyc­er­ine as dynamite. Dur­ing the past 50 years, am­mo­nium ni­trate has played a dra­mat­i­cally in­creas­ing role as an ex­plo­sive. As a safer and sus­tain­able al­ter­na­tive, water gel ex­plo­sives have evolved over the last 25 years as com­mer­cial ex­plo­sives.

En­vis­ag­ing the con­struc­tion of twin tun­nels un­der the Thames River, between 1820 and 1865, Bri­tish engi­neers Marc Brunel and James Great­head de­vel­oped mod­els of a tun­nelling shield. To sus­tain con­struc­tion speed and safer op­er­a­tions, ground sta­bi­liza­tion tech­niques evolved over time. The tech­nique of freez­ing the soil by cir­cu­lat­ing a coolant through the pipes was in­tro­duced in 1900 in USA.

In­jec­tion grout­ing into soils and weaker rocks was in­tro­duced in the 1970s as a mech­a­nism for wa­ter­proof­ing and ground improvement. Con­crete, ini­tially used in the dry form (Gu­nit­ing) in 1907, de­vel­oped into its wet form (Shotcret­ing) in 1950. These were uti­lized both as pre­lim­i­nary and fi­nal lin­ing op­tions for tun­nels.

In 1931, the first drilling jum­bos were de­vised to dig tun­nels that would di­vert the Colorado River around the con­struc­tion site for the Hoover Dam. These jum­bos con­sisted of 24 - 30 pneu­matic drills mounted on a frame welded to the bed of a truck. Mod­ern jum­bos al­low a sin­gle op­er­a­tor to con­trol sev­eral drills mounted on hy­drauli­cally con­trolled arms.

In 1954, while build­ing diver­sion tun­nels for the con­struc­tion of a dam in South Dakota, James Rob­bins in­vented the tun­nel bor­ing ma­chine (TBM), a cylin­dri­cal de­vice with dig­ging or cut­ting heads mounted on a ro­tat­ing front face that grinds away rock and soil as the ma­chine creeps for­ward. Mod­ern TBMs are cus­tom­ized for each project by match­ing the types and ar­range­ment of the cut­ting heads to the site ge­ol­ogy. Also, the di­am­e­ter of the TBM must be equal to the di­am­e­ter of the de­signed tun­nel (in­clud­ing its lin­ing).

Ad­vanc­ing tun­nelling in In­dia

The tun­nelling his­tory in In­dia is not dif­fer­ent from the tun­nelling his­tory of HCC. HCC’s long-stand­ing ex­per­tise in tun­nelling dates to the in­cep­tion of the com­pany in 1926. Un­der­tak­ing its first con­tract in 1926, HCC con­structed the Bhoreghat Tun­nel on the Mum­bai-Pune Rail­way line in 1928. Evolv­ing since then and never look­ing back, HCC, to its credit, has served the na­tion and the neigh­bour­ing coun­tries by build­ing over 290 km of tun­nels for most civil engi­neer­ing ap­pli­ca­tions across chal­leng­ing and un­cer­tain ge­olo­gies, ex­treme cli­matic con­di­tions, us­ing state-ofthe-art tech­nolo­gies and prac­tices.

With its un­flinch­ing de­ter­mi­na­tion, HCC has ma­tured its un­der­stand­ing of tun­nelling, start­ing with clas­si­cal meth­ods, the el­e­men­tary drill and blast method, the cut and cover method, the New Aus­trian Tun­nelling Method (NATM), shields and tun­nel bor­ing ma­chines and spe­cial meth­ods. With a con­tri­bu­tion of one fourth of the na­tion’s hy­dro power con­struc­tion, HCC’s 290 km of tun­nelling ex­pe­ri­ence can be di­vided as fol­lows – 3% with the cut and cover method, 69% with the drill and blast method, 24% with the Tun­nel Bor­ing Ma­chine (TBM), and around 4% with the NATM method. The tun­nel con­struc­tion ex­pe­ri­ence includes ma­jor civil engi­neer­ing ap­pli­ca­tions viz. hy­dropower gen­er­a­tion, water sup­ply, ir­ri­ga­tion and trans­porta­tion in­fra­struc­ture such as roads, rail­ways and met­ros.

Deal­ing with var­ie­gated ge­ol­ogy

Con­struct­ing tun­nels through var­i­ous ge­o­log­i­cal for­ma­tions in In­dia and its neigh­bour­ing coun­tries, HCC has a great deal of ex­pe­ri­ence in deal­ing with pro­por­tion­ate and oc­ca­sion­ally dis­pro­por­tion­ate mag­ni­tudes of un­cer­tain­ties and risks. This includes tun­nelling in soils that are rel­a­tively younger, as­sorted ge­o­log­i­cal for­ma­tions in the Hi­malayan re­gion, the Pleis­tocene area, Dec­can Trap, Gond­wana, Vind­hwan, Al­lu­viam areas and pre-Cam­brian ge­olo­gies. The risk of con­struc­tion has been present in al­most all the seis­mic zones of In­dia.

En­coun­ters with the Hi­malayan moun­tains

Tun­nelling through frag­ile, weak and jointed rock masses of the Hi­malayas is of­ten chal­leng­ing for plan­ners, de­sign­ers, engi­neers, ge­ol­o­gists and, most im­por­tantly, con­struc­tion con­trac­tors. This is pri­mar­ily due to high over­bur­den, thickly veg­e­tated and in­ac­ces­si­ble ter­rains, var­ied rock for­ma­tions, pres­ence of small and big shear zones/thrusts, and as­so­ci­ated hy­dro­log­i­cal chal­lenges. Tun­nelling in such re­gions in­vites mul­ti­ple, of­ten un­fore­seen prob­lems such as face col­lapse, chim­ney for­ma­tion, water-in­rush, hot water springs, gas ex­plo­sion, squeez­ing and so on. Deal­ing with such is­sues ne­ces­si­tates re­spon­sive and “on the toes” engi­neer­ing and con­struc­tion, of­ten re­quir­ing sleep­less vigil and pres­ence of mind. To al­le­vi­ate and sur­mount such chal­lenges, HCC has built sound con­struc­tion prac­tices that in­clude de­tailed ge­o­log­i­cal ex­plo­rations, sta­teof-the-art de­signs, adapt­able tun­nelling prac­tices, in-depth knowl­edge of mon­i­tor­ing, and feed­back sys­tems and mech­a­nisms with an in-built cul­ture of safety.

First suc­cess­ful TBM in Hi­malayan re­gion - a world record: Un­der­tak­ing one of the long­est con­structed tun­nels in In­dia (23.65 km length and 6 m dia) with a max­i­mum over­bur­den of 1,470 m, HCC uti­lized a dou­ble shield TBM for its Kis­hanganga hy­dropower project. Com­plet­ing 14.75 km of tun­nel, HCC cre­ated a world record of be­ing the first suc­cess­ful TBM op­er­a­tor in the Hi­malayan re­gion in a record time of 24 months, with an av­er­age monthly progress of 406 m. While deal­ing with ad­verse ge­olo­gies, HCC also cre­ated a na­tional record of the high­est monthly progress in tun­nelling of 816 m in the month of Oc­to­ber 2013. The re­main­ing length of 8.89 km was con­structed us­ing the drill and blast method.

Build­ing na­tion’s long­est trans­porta­tion tun­nel: En­trusted with the re­spon­si­bil­ity of build­ing the long­est rail­way tun­nel, Pir Pan­jal (J&K), HCC uti­lized the NATM method for deal­ing with rugged ter­rains of the Pir Pan­jal re­gion, con­nect­ing Bich­leri Val­ley on the south side and the Kash­mir Val­ley on the north. In this chal­leng­ing and mar­vel­lous project in the his­tory of Indian Civil Engi­neer­ing, many ge­o­log­i­cal sur­prises and chal­lenges were faced in the rel­a­tively younger Hi­malayan ge­ol­ogy. This sta­teof-the-art tun­nel of 11.125 km is 100% wa­ter­proof and equipped with the lat­est fire fight­ing sys­tems. As an ac­co­lade for com­plet­ing this project, HCC was awarded two more projects along the same align­ment.

Worst ge­ol­ogy en­coun­tered so far: Deal­ing with the sub-Hi­malayan areas in Bhutan and some of the treach­er­ous me­dian to heavy zones of soil, HCC has suc­cess­fully un­der­taken projects in Bhutan. Dur­ing the con­struc­tion of Da­gachhu Hy­dro Power Project in Bhutan, HCC engi­neers ex­pe­ri­enced one of the most chal­leng­ing ge­ol­ogy. The ground strata were not ad­e­quate to hold the struc­ture as there were sev­eral water cour­ses be­neath the sur­face and the land was marshy. In­cli­nome­ters and geotech­ni­cal equip­ment to mea­sure un­der­ground move­ments/de­for­ma­tions and ex­ten­sive mon­i­tor­ing sys­tems were used. The re­sults re­vealed that the land had sig­nif­i­cant un­der­ground move­ments.

To deal with this sit­u­a­tion, the align­ment of the head race chan­nel was changed, and soil sta­bi­liza­tion was uti­lized to im­prove the foun­da­tions with ad­di­tional shotcrete and spe­cial an­chor­ing. At the Head Race Tun­nel, var­i­ous sup­port sys­tems such as rock bolts, wire mesh with

shotcrete, steel ribs, lat­tice gird­ers and winches were used in vary­ing quan­ti­ties. Fre­quent en­coun­ters of this type made this project very chal­leng­ing and added great value to HCC’s ex­pe­ri­ence.

Serv­ing ur­ban trans­port

Tun­nelling in ur­ban grounds is com­plex and chal­leng­ing, of­ten due to con­struc­tion in soft soils, ex­ist­ing ur­ban in­fra­struc­ture, pres­ence of high-rise build­ings, pub­lic util­i­ties and, most im­por­tantly, safety for hu­man life. HCC has built In­dia’s first metro rail project at Kolkata, wherein 5.33 km of stretch was built us­ing the cut and cover method, and a length of 1.14 km us­ing the shield tun­nelling method.

HCC has been in­volved in the con­struc­tion of five un­der­ground sec­tions, which are a part of the strate­gic plan of Delhi Metro Rail Cor­po­ra­tion (DMRC). 4.47 km of stretch was built us­ing the cut and cover method and a length of 10.30 km us­ing the shield tun­nelling method. The key to de­vel­op­ing such de­signs is an un­der­stand­ing of tun­nelling-in­duced ground loss mech­a­nisms and the as­so­ci­ated dis­place­ments, and the risks they pose to ad­ja­cent build­ings, struc­tures and util­i­ties. The route align­ment for this metro line passed be­low var­i­ous her­itage struc­tures and build­ings of na­tional im­por­tance.

In its en­deav­our to serve the na­tion faster and keep its time com­mit­ment, HCC has de­ployed five TBMs at Delhi Metro, of which, four are op­er­a­tional at CC34 pack­age, in­volv­ing 4.4 km long twin tun­nels on Janakpuri West–Kalindi Kunj Cor­ri­dor, and one is op­er­a­tional at CC30 pack­age, in­volv­ing 2.2 km twin tun­nels between Shal­i­mar Baug and Sub­hash Place sta­tions.

Meet­ing di­men­sional chal­lenges

Largest di­am­e­ter Tun­nel Bor­ing Ma­chine de­ployed by HCC: For con­struct­ing a 19.2 km long tun­nel for Pula Sub­ba­iah Veligonda ir­ri­ga­tion chan­nel in Andhra Pradesh, HCC de­ployed a 10m di­am­e­ter Dou­ble Shield Tun­nel Bor­ing Ma­chine of Rob­bins make. The con­tin­u­ous lin­ing be­hind the ma­chine con­sists of 300 mm thick con­crete seg­ments in 6+1 ar­range­ment, mak­ing the fin­ished tun­nel di­am­e­ter 9.2m. The tun­nel path was lo­cated in sed­i­men­tary rock with a num­ber of faults and folds with some ground water. A probe drill mounted on the ma­chine al­lowed for ver­i­fi­ca­tion of the ge­ol­ogy 30m ahead of the TBM. A strict pro­gramme of probe drilling com­bined with ad­e­quate ground sta­bi­liza­tion al­lowed the TBM to ad­vance through dif­fi­cult sec­tions of rocks.

Small­est and largest di­am­e­ter tun­nels: The small­est di­am­e­ter tun­nel con­structed by HCC was for Bri­han­mum­bai Municipal Cor­po­ra­tion. It was a 2.74 km long sewage tun­nel with a fin­ished di­am­e­ter of 2.5m, con­structed us­ing a shield TBM and lined with pre­cast con­crete seg­ments. Tun­nelling chal­lenges in­cluded mas­sive and weath­ered basalt as well as the ground­wa­ter level along the tun­nel align­ment. A Her­renknecht Hard Rock TBM of 3.065m di­am­e­ter with in­te­gral au­to­matic grout in­jec­tion sys­tem was used for the con­struc­tion of this tun­nel. For the first time in In­dia, a shielded hard rock TBM and the gas­keted lin­ings were used in this project.

The largest di­am­e­ter tun­nel con­structed by HCC was for the Nathpa Jhakri Hy­dro­elec­tric Power Project. The 1530 MW project boasts of the largest and long­est Head Race Tun­nel (HRT), the largest de­silt­ing cham­bers, the deep­est and the largest surge shaft, and the largest un­der­ground power com­plex. Of the to­tal length of the 27.4 km HRT, HCC was in­volved in the con­struc­tion of the 11.33 km long con­crete lined HRT of 10.15m fin­ished di­am­e­ter. Ex­ca­va­tion of the HRT was car­ried out by the drill and blast method. The com­pany also con­structed the deep­est surge shaft in In­dia for this project, which was 301m in depth and 21.6m in di­am­e­ter.

World record in long dis­tance con­crete pump­ing for tun­nel lin­ing

HCC cre­ated a world record in hor­i­zon­tal long-dis­tance con­crete pump­ing while con­struct­ing the Head Race Tun­nel for the Sainj Hy­dro­elec­tric Power Project in Hi­machal Pradesh. The con­crete was suc­cess­fully pumped for a dis­tance of 2,432 m. The main rea­son be­hind opt­ing for the longdis­tance con­crete pump­ing method­ol­ogy was the rel­a­tively smaller di­am­e­ter of the tun­nel. At 3.85 m fin­ished di­am­e­ter, the two-way si­mul­ta­ne­ous move­ment of tran­sit mix­ers was not pos­si­ble, ef­fec­tively rul­ing out the con­ven­tional method of con­cret­ing. The project team tack­led the chal­lenges with precise plan­ning, com­men­su­rate test­ing, train­ing, re­spon­sive engi­neer­ing and, most im­por­tantly, seam­less co­or­di­na­tion among the team mem­bers to achieve this ma­jor feat.

The way ahead

With In­dia’s strate­gic in­fra­struc­ture de­vel­op­ment plans on their way to im­ple­men­ta­tion, there is great scope for tun­nelling in In­dia, es­pe­cially for de­vel­op­ing ur­ban in­fra­struc­ture, un­der­ground rail and road net­works, trans­porta­tion in moun­tain­ous re­gions and so on. Re­fine­ments in de­sign­ing ca­pa­bil­i­ties and the abil­ity to uti­lize in­stru­men­ta­tion data will en­hance our abil­ity to fore­see un­cer­tain­ties and risks. In or­der to bet­ter ac­cess risks and un­cer­tain­ties, de­tailed ge­o­log­i­cal ex­plo­rations will have to take deeper root. A greater level of mech­a­ni­sa­tion of tun­nels will re­duce con­struc­tion time and help early rev­enue gen­er­a­tion.

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