Rock mechanics and tunnelling engineering

Rock mechanics and tunnelling

1. Introduction to tunnelling

2. The 24.5km Laerdal tunnel in Norway is the world’s longest road tunnel.

3. Delaware Aqueduct, 137,000 m (85.1 mi)

4. Guangzhou Metro Line 3, 57,930 m (36.0 mi)
https://en.wikipedia.org/wiki/List_of_longest_tunnels

5. Tunnel
Itisanundergroundorunderwaterpassageway,dugthroughthesurrounding
soil/earth/rock.
Atunnelisanundergroundpassageway,dugthroughthesurroundingsoil/earth/rockand
enclosedexceptforentranceandexit,commonlyateachend.
Atunnelmaybeforfootorvehicularroadtraffic,forrailtraffic,acanalorutilitycorridor..
Requiredwhenopenexcavationofstratabecomesuneconomical,notonlyconstruction
costbutformaintenanceaswell.
Tunnelisanartificiallyconstructedundergroundpassagetoby-passobstaclessafely
withoutdisturbingtheoverburden.
Tunnelsarealsoerectedwhenshortestrouteconnectionisneededincities.

6. Tunnellingisaformofcivilengineeringconstruction,carriedoutinanuncertainandoften
hostileenvironment,andrelyingontheapplicationofspecialknowledgeandresources.
CIRIA(1978)
Tunnelsaretypicallylong,oftenverylong,relativetotheirdiameterandthisis
fundamentallyimportanttothewaythatthegroundcanbeinvestigatedandthe
Designcanbeconducted.

7. Tunnels are necessary in the context of transportation for the following Purposes:
•To avoid a long circuitous route around a mountain or spur;
•To avoid slips of slides of open cuts in soft strata;
•To avoid steep gradients in hilly terrain;
•To avoid crossing precipitous ridges or high peaks or zones likely to be under snow for a major
part of the year;
•To avoid acquisition of valuable property or to avoid interfering or damaging a heritage
structure.
However, tunnels are associated with some disadvantages, such as:
•High initial cost;
•Long construction period;
•Specialised work, needing special equipment and highly skilled labour.

8. Atal Tunnel is a highway tunnel built under the Rohtang Pass in the eastern PirPanjalrange of the Himalayas on the
Leh-Manali Highway in Himachal Pradesh, India. At a length of 9.02 km, it is the longest tunnel above 10,000 feet in the
world

9. Thegeologicalfactorsconsideredintunnellingprojectsareasfollows:
•Theeaseofextractionoftherocksandsoils;
•Thestrengthoftherocksandtheneedtosupportthem;
•Theamountinadvertentlyexcavatedbeyondtheperimeterofthetunneloutline
(thatis,overbreak),particularlywhereexplosivesareused;
•Thegroundwaterconditionsandtheneedfordrainage;and
•Thetemperatureinverydeeptunnelsandtheneedforventilation
Theamountordegreeofchangeintheseconditionsalongthetunnellinecanbeas
importantinplanningandcostsastheiraverageormaximumvalues.

10. Euphrates Tunnel
TheEuphratesTunnelwasalegendarytunnel
purportedlybuiltbetween2180and2160BCEunder
theriverEuphratestoconnectthetwohalvesofthe
cityofBabyloninMesopotamia.
TheexistenceoftheEuphratesTunnelhasnotbeen
confirmed.

14. Name
Track length
(m)
Station Station StateRailway Division
Year of
Opening
Patalpani Rail Tunnel14,000
Patalpanirailway
station
Balwada Madhya PradeshWestern Railway2025
Pir Panjal Railway Tunnel11,215
Banihal railway
station
Hillar Shahabad
Jammu and
Kashmir
Northern Railway2013
Trivandrum Port Tunnel9,020 Vizhinjam Balara Kerala Southern Railway2022
Sangaldan Tunnel 8,000 Sangaldan Kohil
Jammu &
Kashmir
Northern Railway2020
Rapuru (P-4) 6,642.25Vellikallu CherlopalliAndhra Pradesh
South Central
Railway
2019
Karbude (T-35) 6,506 Ukshi Bhoke MaharashtraKonkan Railway1997
Maliguda Tunnel(M-1) 4,422.25Jeypore Maliguda Odisha
East Coast
Railway
1963
Nathuwadi (T-6) 4,389 Vinhere DiwankhavatiMaharashtraKonkan Railway1997
Tike(T-39) 4,077 Ratnagiri Nivasar MaharashtraKonkan Railway1997
Berdewadi(T-49) 4,000) Adavali Vilavade MaharashtraKonkan Railway1997
Rail tunnels in India by length

15. ParsikTunnel
TheParsikTunnelisa1.317km(0.818mi)long
electrifieddual-linerailwaytunnelwhichlocatesin
ParsikHillofThane,Maharashtra,India,lieseasttothe
Thanecity,andalsoapartofCentralline.
GreatIndianPeninsulaRailwaystartedconstructionof
thistunnelin1906,ittooktime10yearstoconstruct
thetunnelandopenedattheyear1916
Aftertheconstructionofthetunnel,itbecamethethird-largesttunnelinAsiaintheyear
1916.

16. Classification of Tunnel
A.Classificationoftunnelbasedonpurpose
B.Classificationoftunnelsbasedonshape
C.Classificationoftunnelsbasedonalignment
D.Classificationbasedontypeofmaterialmetwithinconstruction

17. A)Classificationoftunnelaccordingtopurpose
a.Conveyancetunnels
b.Traffictunnels
c.Minetunnels

18. a.Conveyancetunnels
Thesetypeoftunnelsmainlyconstructedforwatersupply,sewagelines,andhydro-electric
powersupply.
•Hydroelectricpowerstationtunnel
•Watersupplytunnels
•Sewertunnels
•TunnelsfortransportationinIndustrialplants

19. b.Traffictunnels:
Itincludeshighwaytunnels,railwaystunnels,pedestrian,navigationtunnelsandsubway
tunnels.
•Railwaytunnels
•Highwaytunnels
•Pedestriantunnels
•Subwaytunnels
•Navigationtunnel

20. c.Minetunnels:Itisusedformineral,ores,andmetalextractionfromthecrust.Theyare
cheapertobuildincomparisontoothertunnels.

21. Conveyance Tunnels

22. Traffic Tunnels

23. B)Classificationoftunnelsaccordingtoshape
a.Circularshapedtunnels:
b.Horseshoetunnels
c.D-shapedtunnels
d.Ellipticaltunnels
e.Rectangulartunnels
f.Egg-shapedtunnels

24. a.Circulartunnel:
Besttoresisttheexternalorinternalforce.
Itprovidesthegreatestcross-sectionalareafortheleastperimeter.
Circularshapetunnelsnotsuitableforrailways,andhighwaytransportationmainlyusedfor
sewagelines.
Morefillingisrequiredtoformaflatbasefordesigningaroadorrailwaytrack.
Liningworkisverydifficult.

25. b.HorseShoeTunnels
Horseshoetunnelscanwithstandinternalandexternalpressures.
Semi-circularroofwitharchedsidesandcurvedinvert.
Mostsuitableforsoftrocks
Mostwidelyusedforhighwayandrailwaytunnelsandcanbeusedtocarrywaterorsewage

26. c.D-ShapedTunnels:
Tunnelconstructiontopassawaterwayunderneathahigherterrainorfornavigation
tunnels.
AdditionalfloorSpaceandflatfloorformovingequipment.
Mostsuitedinrocktunnels.

27. d.EllipticalTunnels
Thesmallercrosssectionatthebottommaintainflowattherequiredselfcleaningvelocity.
Suitableinsoftermaterial(soilcomparedtorocks).

28. e.RectangularTunnels
Rectangulartunnelssuitableforhardrocksitesandmainlyusesforpedestrianpassage.
Thesetunnelsarerelativelycostly.
Notsuitabletoresistexternalpressureduetotheirrectangularshapeandthesearenotin
usethesedays.

29. f.Egg-ShapedTunnels
Eggshapedtunnelssuitableforsewagelinesastheyhaveselfcleaningvelocityindryweather.
Itcanresistexternalaswellasinternalpressure.
Notsuitableastraffictunnels
Theconstructionprocessofthesetunnelsareverydifficult

30. C) Classification of tunnels based on alignment
a.Off-Spurtunnels:Shortlengthtunnelstonegotiateminorobstacles.
b.Saddleorbasetunnels:Constructedinvalleysalongnaturalslope.
c.Slopetunnels:Constructedinsteephillsforeconomicandsafeoperation.
d.SpiralTunnels:Constructedinnarrowvalleysinformofloopsininteriorof
mountainssoastoincreaselengthoftunneltoavoidsteepslopes.

31. Saddle or base tunnels Slope tunnels
Off-Spur tunnels

32. Slope tunnels

35. BNSF Flathead Tunnel 337 km
New Cascade Tunnel 531 km
BNSF Nelson Bennett Tunnel 638 km
BNSF Boysen Railway Tunnel 1085 km
Spring Garden Tunnel 1328 km
Bootlegger Tunnel 1523 km
MoffatTunnel 1524 km
Santa Susana Railroad Tunnel 1919 km
Crest Tunnel 2475 km
TúnelFerroviario2805 km

36. D. Classification based on type of material met with in construction
a.Tunnelsinhardrock
b.Tunnelsinsoftmaterials
c.Tunnelsinwaterbearingsoils

37. Technical terms used in Tunnelling
Adit:Atunneloropencutdrivenfromthesurfacetothemaintunnelforprovidingaccess
oradditiontothenumberofworkingfacesofthemaintunnel.
Cuthole:Groupofholesfiredfirstinaroundofblastingtoprovideadditionalfreefacesfor
thesucceedingshots.
Detonator:Acatalystusedforactivatingahighexplosivecharge.Catalystitselfisactivated
byasafetyfuseorbyelectricity.
Drillingpattern:Alayoutarrangementshowinglocation,directionanddepthoftheholes
drilledintothefaceofatunnel.
Scaling:Operationofremovalofalllooserocksandbitsfromthebastedsurfaceafter
blastingiscompleted

38. Explosive:Anymixtureofchemicalcompoundswhichiscapableofproducinganexplosionbyits
ownenergy.(Itcanbeblackpowder,dynamite,nitroglycerinecompounds,andanyfulminateor
explosivesubstancehavingexplosivepowerequaltoorgreaterthanblackpowder.)
Blocking:Fillinggapbetweentheexcavatedrocksurfaceandtheribstotransferthe(externaland)
rockloadtotheribs.
Rockload:Heightofmassofrockwhichexertspressureonthesupport(andlining).Thisis
computedtakingintoconsiderationnatureofrockandsize/shapeoftunnel.
Tunnelsupport:Structureerectedinsidethetunneltosupportthestrataaboveandaroundthe
excavatedcavity,tillthe(permanentsupport)liningisplaced.
Theyinclude:(a)supportswhichareleftinplaceand/orembeddedpermanentlyor(b)temporary
supportswhichareerectedduringexcavationandremovedbeforeorduringerectionofeitherthe
permanentliningorprovidingpermanentsupports.

39. Softstrata:Stratarequiringsupportstobeinstalledwithinaveryshortperiodofexcavation,but
whichatthesametimecannotbeeasilyexcavatedbyhandtools.Theyincludesoftrocks(usually
sedimentaryormetamorphic)whicharejoinedandfaulted.
Trimmer(hole):Holesdrilledontheperipheryofanexcavationandfiredforachievingtheintended
finaloutlineofexcavation.
Stemming:Inertmateriallikeclayusedforpackingtheshotholeoverthelastexplosivechargeup
toitsouterend.
Cover:Coveronatunnelinanydirectionisthedistancefromthetunnelprofiletotheoutermost
groundsurfaceinthatdirection.
Ifthethicknessoftheoverburdenislarge,(morethanthreetimesthediameterofthetunnel)its
equivalent,asdeterminedintermsofthedensityofrockmayalsobetreatedascover.

40. Benching:Operationofexcavationinthelowerportionofthetunnelsectionafterthetop
headinghasbeendriven.
Bracing:Structuralframeconnectionprovidedbetweenribs/poststopreventthelatterfrom
bucklingorshifting.
Heading:Generallyappliestothefaceofthetunnelwhereactualtunnellingoperationsare
inprogress.Ifitisprefixedbytheword'top’or'bottom',itdenotesthatpartofsectionof
thetunnelexcavatedfirst/inadvance