Engineering Geology

Norway extends some 2100km from its southern tip tothe far north-east corner. The landscape and topographyis characterised by deep valleys, high mountains andlong and deep fjords, constituting numerous challengesto overcome for infrastructure construction. Thereforethere is a need for tunnels to accommodate efficientcommunication. Most of the Norwegian electric energyis generated by hydropower, thus there is also a greatnumber of tunnels associated with such projects. Thetotal length of Norwegian tunnels is more than 5000km,and that means that there is about one meter of tunnelfor each inhabitant. In addition to tunnels there are hun-dreds of caverns for different use, such as storage for oil

and gas, cold storage, shelters, parking halls, sports hallsand power stations.

The tunnelling industry in Norway started in the 16thcentury in connection with increased metal miningactivities. Most metal mines are now history, but theyhave been replaced by mining of so-called industrialminerals, i.e. minerals used for a large range of productslike cement, glass and ceramics, fillers for paper,pigments for paints etc. At the moment, 20 undergroundmines on industrial minerals are operating, producingabout 5 million tonnes or 2 million m3 annually.

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1 INTRODUCTION

Type Number Length, km

Railway tunnels 700 316

Road tunnels 881 843

Hydropower projects >300 3500

Industrial mineral mines 20 -

Other tunnel projects approx. 200 250

Total >2100 5000

Table 1.1. Tunnels in Norway

Table 1.2. Different types of caverns and tunnels

Type Number Length, kmSub-sea tunnels 34 130

Sub-sea road tunnels 23 95

TBM tunnel projects 28 260

Underground hydropower stations approx. 200 -

Air cushion chambers 10 -

Water pressure tunnels (> 150m pressure) 80 -

Industrial mineral mines Not available Not available

Oil and gas stores 10 -

Most of the rocks in Norway have an age of more than350 million years. Highly metamorphic rocks ofPrecambrian age such as granite, gneiss and gabbroconstitute about 70% of the area. The remaining bedrockconsists of more or less metamorphic rocks of Cambro-Silurian age such as schist, greenstone, sandstone andmarble.

Uunaltered sedimentary rocks may also be found, how-ever, in rather limited areas, such as in the close sur-roundings of Oslo. Here there are also unaltered vol-canic rocks such as basalt and rhombus porphyry ofPermian age.

The Norwegian bedrock has a complex tectonic history,and because of intense folding and metamorphism thestructural pattern and discontinuities exposed today isoften complex. This means that a lot of different rocktypes and structural features can be encountered in atunnel. Usually the bedrock is of good quality as far asstability is concerned, but locally there might be nume-rous discontinuities in terms of joints and weaknesszones. Such weakness zones can be faults with crushedrocks that may be more or less altered to clay. Swellingclay (montmorillonite) is often found in such zones.

Stability problems are therefore often related to thehandling of joint systems in general whilst sections ofthe tunnels with weakness zones may face more severeproblems. Norwegian tunnellers have recently handledextreme tunnelling conditions in the Oslofjord tunnelneccessitate ground freezing and extensive rock massgrouting to stabilise a difficult zone.

In a section of the Bjory tunnel near Bergen, themethods used had elements of soil tunnelling. SeeAppendix 3 for details on the Oslofjord project and theBjory tunnel.

High in-situ stresses may cause poor stability over longtunnel sections. The stress induced stability problemsare partly caused by high rock cover, for example in thefjord landscape of Western Norway, but several placesthere are in addition high tectonic stresses, thus over-stressed rock masses may be encountered even at lowrock cover. Solutions for dealing with high stress aniso-tropy by using rock bolts and sprayed concrete havebeen developed, as was used for the Lrdal tunnel.

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2 ENGINEERING GEOLOGY OF NORWAY

Figure 2.1. Kobbvatn area in Northern Norway. The rock is amassivePrecambrian granite with high stress anisotropy.(NGI)

Another consequence of the Norwegiannature is the generous precipitation andmost of Norwegian tunnels are located inthe saturated zone in the rock mass. Thus,handling water inflow and ground waterhas been a normal procedure of Norwegiantunnelling projects.

Soft rock, in any greater extent than inweakness zones, is seldom encountered inNorwegian tunnels. Such zones may, howe-ver, be several tens of meter wide and callfor extraordinary support measures and tun-nelling methods. Strongly weathered rocksnear the surface do usually not occur sincesuch material was mainly eroded and remo-ved by the glaciers during the Quaternaryglaciations. The rock mass appears therefo-re usually fresh, even on surface outcrops.

Norwegian tunnelling projects have faced agreat variety of ground conditions includingalso adverse and problematic tunnelling, butin overall the condition for tunnels are con-sidered being favourable in Norway.

NORWEGIAN TUNNELLING SOCIET Y PUBLICATION NO. 14

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Figure 2.2. Geologicalmap of Norway

Table 2.1. Typical mechanical properties of Norwegian rocks

Rock type Uniaxial compressive strength(MPa)

Point load index(tensile strength)(MPa)

Youngs modulus(GPa)

Poissons ratio

Amphibolite 110 12 70 0.20

Diorite 150 14 50 0.15

Gneiss 130 15 45 0.18

Granite 170 15 40 0.15

Greenstone 100 10 55 0.20

Limestone 75 8 70 0.30

Mica schist 70 8 30 0.20

Phyllite 35 6 30 0.10

Quarzite 170 15 55 0.15

Sandstone 150 15 30 0.20

Starting in the last decade of the 19th century and con-tinuing into the first half of the 20th century significantdevelopment of the railway system took place. The493km long railway line between Oslo and Bergen withits 184 tunnels was opened in 1909. Most of the hydro-power tunnels were built between 1950 and 1990. In the1970s the Norwegian oil and gas era began and the

experience of tunnelling enabled the application ofunderground storage, transport tunnels and pipelineshore approaches for hydrocarbon products. During thelast two decades of the 20th century construction ofmany large road tunnel projects have been realised, andseveral sub-sea tunnels for communication to islandsand crossing of fjords have been excavated.


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Figure 1.1. Tunnel excavation in Norway over the last 32 years

0

1

2

3

4

5

6

2002200019981996199419921990198819861984198219801978197619741972

Volume (m )

3)

Railway Highway Underground/Metro Water supply Hydropower

Sewage Storage caverns Others Estimate 1974

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3.1 Hydropower schemes3.1.1 GeneralThe climate and nature in Norway allows for extensivedevelopment of hydropower schemes and the annualoutput from hydropower production is about 121TWh,constituting nearly 100% of the electric power supply.The development of hydropower started back in 1885.Tunnels have been used to various extent in some 300hydropower projects with a total tunnel length of about3500km.

See Appendix 1 for details on reference projects and listof publications on this theme.

3.1.2 Underground stationsSome 200 underground hydropower stations have so farbeen constructed in Norway, and this is about half thetotal number of underground stations found world wide.The advantages of underground hydropower stations aremainly associated with better sheltering and reducedmaintenance cost compared to facilities placed aboveground. Especially during the cold war the securityaspect was of importance. It is also usually possible toselect a location for the underground station where thegeological conditions are favourable.

The first underground hydropower station that was builtin Norway, Bjrksen near Narvik, was built in the years1919-1923, and since 1950 the typical design has beento locate hydropower plants underground.

Underground hydropower stations are designed with aspecial type of cavern layout. The cavern span is usual-ly 15-20m and the height is 30-40m, and a two-cavernsolution with the transformer station in a cavern parallelto the powerhouse is also often used, see Figure 3.1.

3.1.3 Unlined pressure shafts and air cushion chambers

Figure 3.2 shows the development of the general layoutof hydropower plants in Norway.

Before 1950 underground power stations were ratherunusual, and from the headrace tunnel there was a pen-stock on the surface.

From 1950 and onwards most of the installations weremoved underground and the surface penstock was sub-stituted by a steel-lined pressure shaft.

To obtain cost savings, alternative solutions to reducethe length of the steel-lining were looked at, and unlinedpressure shafts were tried as early as 1920, but it was notuntil 1960 that this became the common solution. Atpresent, more than 80 unlined shafts/tunnels with awater head larger than 150m are in operation, with1080m water head as the highest. To prevent water see-page into the powerhouse, the last part of the headracetunnel nearest to the powerhouse must be equipped witha steel lining. The length of this lining depends on thewater pressure, but is usually in the range of 30-80m.The access tunnel leading to the unlined pressure shaftmust be confined with a concrete plug, normally 10-25m long, to withstand the water pressure. A manhole isinstalled in the concrete plug to allow later access.Around the concrete plug and the upper part of the steel-lined shaft high-pressure grouting is carried out, seeFigure 3.3. The grouting pressure must be in the samerange as the water pressure or even higher.

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3 NORWEGIAN TUNNELLING PROJECTS

Figure 3.1. Cross section of a Norwegian power plant

The headrace tunnel system for a hydropower plantneeds a surge arrangement, either an open tunnel/shaftor a closed underground chamber. In most cases thisarrangement has been solved with a surge tunnel fromthe top of the pressure shaft up to the surface. An aircushion chamber near the power station may sometimesconstitute a less expensive solution, and in some casesalso the only practical solution. After 1975 ten air cus-hion chambers have been built. The largest of thesechambers with a total volume of 120 000m3 is found atKvilldal power station. They are all unlined, but nor-mally extensive rock mass grouting has been undertakenand in some cases water curtains (artificial ground watercompensation) are in use.

The headrace tunnel in hydropower projects is comingfrom the reservoir that often is a natural lake. The tailra-ce tunnel from the station is usually ending in a lake orin a fjord. In such cases it will be necessary to pierce thebottom of the lake or the fjord with the tunnel, seeFigure 3.4 and 3.5. The method is also named lake tap.


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Figure 3.2. The development of the general layout of hydro-power plants in Norway(from Broch 1985)

Figure 3.3. Plan of an underground hydropower plant (Broch1985) Lake tap

Figure 3.4. Principle of lake tap (Buen 1988)

Figure 3.5.Piercing of the tailrace tunnel for Jostedalenhydropower plant at 40m depth in Gaupnefjorden (Statkraft)

This has been a regular practice in Norway for nearly100 years. It is assumed that about 500 such lake tapshave taken place. The deepest piercing for hydropowerprojects was carried out at a depth of 105m at Juklapower plant in Western Norway. A piercing is locatedwhere the rock quality is favourable and soil thickness issmall. Exploratory drilling, grouting and careful blas-ting are techniques applied to bring the tunnel close tothe rock surface. The final blast has at least two parallelholes cuts and high-strength water-resistant explosivesare used. In the most common piercing method an aircushion is established below the final plug to reduceshock waves on gates and bulkheads. The principles oflake taps have also been applied for shore approacheswhere pipelines with oil and gas from the oilfields in theNorth Sea approach land, see chapter 3.4.

3.2 Railway tunnels More than 700 railway tunnels with a total length of316km have been constructed in Norway. Most of thesetunnels were built before 1950. The longest railway tun-nel is the double track 14km long Romeriksporten tun-nel on the line between Oslo and the airport atGardermoen and it was opened for use in 1998. At thesame time the extension to double track at the south-bound railway from Oslo included excavation of severaltunnels. Tunnelling works are still going on (2004) atmajor railway projects west of Oslo.

The railway through the city centre of Oslo is also part-ly underground with a 3.6km long double track tunnel,including the National Theatre station. This station con-sists of two parallel caverns, each with a span of 20m,and both partly with only a few metres of rock cover. Inaddition the metro system in Oslo has about 10km oftunnels and several underground stations.


3.3 Road tunnels The Norwegian road network consists of more than 800road tunnels with a total length of 840km. Most of thesetunnels were built during the last 50 years. The tunnelsinclude a great variety in lengths, cross-sections, trafficdensity, standard and geological conditions. TheNorwegian Public Roads Administration has issued aguideline for use in the design and construction of roadtunnels, see Figure 3.6. This guideline (Handbook 021)provides recommendations on tunnel classes, includingalignments (vertical and horizontal curvatures), cross-sections and installations. Typically, the annual trafficdensity is a governing parameter for the determinationof the tunnel class.

The 24km long Lrdal tunnel, opened in 2000, is thelongest road tunnel in the world, see Figure 3.7(Grimstad, E., Kvle, J.1999). It was designed and con-structed according to Handbook 021 to provide a tunnelfocusing the drivers confidence, comfort and safety,today it is an important link of the road connecting theEastern and Western parts of Southern Norway. The tun-nel goes through Precambrian gneisses with rock coverup to 1500m. The rocks have usually few joints butmajor fault zones and very high stresses locally causedsevere rock stress problems.

For communication to islands and crossing under fjordsnumerous sub-sea tunnels have been excavated, the firstwas opened for traffic in 1983. Since 1983 a total num-ber of 23 sub-sea road tunnels have been built, the long-est being the Bmlafjord tunnel close to Bergen, 7.9kmlong. The deepest tunnel, connecting the islands of Hitraand Frya reaches 264m below sea level. The criticalparameter of minimum rock cover is governed by regu-lations in Handbook 021. A new sub-sea tunnel, theEiksund project, is soon to commence construction andit will reach as deep as 280m below sea level, whilst arecord long sub-sea road tunnel (approximately 24km)crossing the Boknafjord is in the planning stage.


PUBLICATION NO. 14 NORWEGIAN TUNNELLING SOCIET Y

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Figure 3.6. Cross section of a typical Norwegian road tunnel

Figure 3.7. From the Lrdal tunnel (Grimstad)

3.4 Underground oil and gas installations

The traditional way of storing oil products in Norway aswell as in other countries has been in steel tanks aboveground. In the late 1960s the first projects were realisedwhere oil and gas storages were placed in rock cavernsin Norway. During the last 35 years rock caverns havebeen used commonly for oil storage. The total volume ofoil stored in underground caverns is about 5 million m3.In connection with the refinery at Mongstad north ofBergen there is a large number of caverns storing diffe-rent types of oil products, including a crude oil terminalwith a capacity of 9.5 million barrels. In addition theMongstad project involves several gas storage caverns,according to both the chilled and pressurised concepts.

Particularly the technique of unlined caverns has beenpreferred, taking advantage of experience gained fromunlined pressurised tunnels in hydropower projects.Rock mass grouting is needed for sealing of the rockmass and water curtains for hydrodynamic control.

Large combined storage, refinery and terminal facilitiesutilising underground facilities are also in use at Sture(see Figure 3.8) and Krst. In the Oslo area there areseveral unlined caverns storing oil products, and at

Rafnes in South-eastern Norway there is an unlinedcavern with a total volume of 100 000m3 storing pro-pane. In Glomfjord, at the Arctic Circle, there is an unli-ned underground storage for ammonia.

In connection with the landing of oil and gas from theNorth Sea several sub-sea tunnels and shore approachesfor the pipelines have been constructed. These have beenexcavated through varying geology reaching 180mbelow the sea level. Piercing the sea bottom has beennecessary to enable these shore approaches. At Kollsnesnorthwest of Bergen the gas pipeline from the TrollField was taken into a sub-sea tunnel at a water depth of161m. The rock mass was thoroughly grouted before thelast blast rounds. The drilling was performed with a vari-ance of less than 10 by a special constructed hydraulicboring equipment, and the explosives were especiallyprefabricated for each hole.


3.5 Water supply and sewage Tunnels and underground openings have been used forvarious purposes in projects related to water supply andsewage handling. The four major cities of Oslo, Bergen,Stavanger and Trondheim have extensively developedtheir subsurface systems for such purposes.

In Trondheim the main water supply is from the lakeJonsvatnet 10km away from the city centre. A system ofwater tunnels and four underground water tank facilitieshas been constructed to supply the citys population withpotable water. The Hgsen water tank, see Figure 3.9,was excavated in greenstone next to a major fault zone.The rock mass quality was rather poor and it was deci-ded that instead of using two independent singlecaverns, two double caverns should be constructed. Inthis way the span width could be reduced from 12 to 8m.The sewage system in Trondheim has also moved under-ground and consists of several tunnels and two under-ground treatment plants.

Oslo has more than 20km of tunnels for water supplyand two underground plants for water treatment. In theOslo area there are also about 50km of sewage tunnels,most of these are relatively new and have been bored byTBM, and two underground sewage treatment plants.One of these plants is in Precambrian gneiss of goodquality whereas the other is in Ordovician sedimentaryrock of rather poor quality.


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Figure 3.8. Oil cavern, Sture


3.6 Waste storages The largest underground waste storage in Norway islocated in Odda, in Western Norway, see Figure 3.10.The project encompasses storage of waste from the zincproduction in form of slurry which is deposited in rockcaverns. The caverns have a width of 17.5m and a maxi-mum height of 23.5m. The length is varied and thestoring capacity for each cavern varies between 70000m3 and 140 000m3. One year of zinc productionequals 70 000m3 of waste, which means that excavationof caverns must be a continuous process. At the momentabout ten rock caverns have been commissioned. Thismethod of waste storage is considered safer than aboveground deposition of the waste.

A similar, but relatively smaller facility has beenconstructed in connection with a nickel smelter near thecity of Kristiansand. An underground repository for thewaste mud was built underneath the factory. The facilityconsists of two caverns with volumes 11 000m3 and 34000m3 and the rocks are Precambrian gneisses of goodquality.

Since Norway has no commercial nuclear power plants(only two research reactors) the quantity of radioactivewaste is small. The Himdalen repository, which is loca-ted approximately 40km east of Oslo, was built to pro-vide a long term disposal and storage for low and inter-mediate level radioactive waste arising up to the year2030. The repository consists of four rock caverns withcross-section of 138m2 and 55m length.


3.7 Sports halls Several caverns for various sports activities have beenbuilt in Norway. Most of these caverns have a span of20-25m and can be used for handball. The GjvikMountain Hall, built for the Olympic Winter Games in1994, is the largest cavern for public use in the world. Ithas a span width of 61m and a length of 90m locatedonly 25 to 50m underground, see Figure 3.11. Feasibilitystudies included mapping in existing nearby caverns byuse of the Q-system, stress measurements and FEM andUDEC-BB modelling. Subsequent site investigationsincluded cross-hole seismic tomography, stress measu-rements, logging and testing of joints in cores and de-tailed numerical analysis using UDEC-BB for predic-ting performance for comparison with distinct elementnon-linear FEM for verifying performance and com-parison with the distinct element results (Athanasiu andHeimli 1994, Barton and Hansen 1994).

Measured deformations of only 6 to 8mm were veryclose to those predicted, and the stability situation ismainly a result of the high horizontal stress of 4 to 5MPaat cavern depth.


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Figure 3.9. The Hgsen underground water tank inTrondheim. Commissioned 1993. Capacity: 22 000m3

Figure 3.10. Schematic layout of the disposal caverns inOdda (Myrvang 1996)a

The construction cost of an underground sports hall willusually be somewhat higher than for a similar buildingabove ground. Experience indicates that reduced main-tenance costs and energy saving often balance the higherconstruction costs. The fact that above ground space is ascarcity and highly priced in urban areas, is also impor-tant factors favouring underground facilities. In additionthe underground sports halls can be combined with air-raid shelters.


3.8 Rock caverns for civil defence andmilitary purposes

3.8.1 Use of underground solutionsAs a member of NATO, Norway has always put largeefforts in a well updated and modern defence system.Underground caverns and tunnels with adequate rockcover, have been experienced as a very good startingpoint for protection of defence facilities. Full protectioncan only be obtained by application of certain specialequipment and systems. A short description of theNorwegian experience with rock caverns for defencepurposes is given in the following.

Experience gained during World War II showed thatrather simple rock caverns gave surprisingly good pro-tection, even against very large conventional bombs.

Throughout the decades that followed, the developmentin the technique of blasting and excavating rock, maderock caverns a cost effective alternative also for defencepurposes. This coincided with a very active rearmamentperiod that started in 1950 and came to a preliminaryhalt in 2002. This rearmament took advantage of thesignificant technical development in the tunnellingindustry and involved extensive use of rock caverns for


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Figure 3.11. Cross-section of the Gjvik Mountain Hall withexcavation sequences (Bollingmo, Heimli and Morseth 1994)

Figure 3.12. Artistic drawing of 120mm coast artillery gun placed underground and a "pop-up" radar station

the Army, Navy and Air forces. The use of undergroundsolutions typically involved facilities as follows: For the Army: Head quarters, land fortresses, ammuni-

tion stores, workshops for vehicles and guns, commu-nication facilities, close in defence systems.

For the Navy: Docking facilities, work-shops, oil- andfuel storage, ammunition stores, communication- faci-lities, radars.

For the Coastal Defence: Gun-emplacements, torpedobatteries, control room for controlled mine fields,radars.

For the Air Force: Shelters for aircrafts, air defencepositions, work shops, ammunition stores, communi-cation facilities, refuelling systems, liquid oxygen sys-tems.

For the Civil Defence: Public air shelters and combin-ed underground solutions of various sports facilitiesand air shelters.

3.8.2 Strengthening of the rock cavernsRock coverFor an underground defence facility the main protectiveelement is the rock cover. The thickness of the slab ofcompetent rock above a cavern or a tunnel is an impor-tant and decisive parameter for the design and layout ofsuch facilities. Empirical and theoretical methods havebeen developed to calculate required thickness takingvarious bomb loads and bomb types into account. Therock mass quality influences the bombs penetrationdepth.

Portals and entrances leading to a rock cavern constitu-te normally the weak points in the design of an under-ground defence facility as these areas may not have asufficient cover to resist weapon effects. The portals andentrances must be given adequate protection related tothe design loads and various types of underground bombtraps etc. have been developed to reach the desired pro-tection level. The typical weapon loads considered in thedesign of defence facilities are normally caused by theuse of: Conventional weapons Nuclear weapons Chemical weapons Biological weapons

In addition, sabotage and terrorists actions must be con-sidered while designing underground solutions fordefence purposes. However, placing such facilitiesunderground has proved to be beneficial compared totraditional surface solutions, the latter being indeed themost sensitive to hostile actions.

Protection systemsThroughout the years, special protection equipment hasbeen developed in Norway. To day such equipment areavailable to meet all significant weapons effects. Incooperation with USA and other NATO countries, thisequipment is to a great extent tested in large scale. Aftersuccessful testing, equipment must then be approved bythe Norwegian defence authorities. A certificate statingthe protection level etc will then follow the equipment.

A protection system comprises equipment designed fordifferent weapons effects put together.

Blast protectionA variety of different equipments is available such as:blast hatches, blast doors, blast gates and blast valves, allin steel or steel combined with concrete. Further, pene-trations are made for cables etc. through the blast barri-er. The blast protection equipment put together in theblast barrier in the opening to a rock cavern, create theblast protection system.


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Figure 3.13. Cables entering the blast barrier

Ground shock protectionConcerning ground shock, nuclear weapons create thelargest threat to a defence facility inside a rock cavern.In principle two kinds of protection of the building and/or sensitive equipment are used: Overall protection of the building inside the cavern Individual protection of sensitive equipment

The choice of type of equipment will depend on weaponloads and protection level. The overall protection isoften used in large facilities designed to resist an indu-ced ground shock. Such facilities usually house a largeamount of sensitive computers and/or communicationequipment.

Electromagnetic pulse from nuclear weapons (EMP)The rock cover is normally not sufficient for EMP pro-tection, thus particular EMP-protection has to be inclu-ded. A building inside a rock cavern is normally of conc-rete or steel, and the steel reinforcement in the concreteis formed to create a Faraday cage. The spacing of thebars is related to the protection level (20-80 dB dam-ping). A steel building gives normally a very good pro-tection. For the openings in the cage special equipmentis available: EMP doors, EMP honeycomb filters forventilation, EMP penetrations for cables and pipes,EMP locks and EMP arrestors.

TempestTempest is the "nick name" for the enemys possibility tolisten to communications or receive electronic signals.High Tempest protection normally demands steel liningor steel walls. Special treatment for computers and tele-communication equipment is necessary.

Chemical weapons (gas). Radio active fall out.Chemical weapons are considered as a major threat. Allmilitary facilities are therefore equipped with standardgas filters. As for radioactive dust (fall out) the gas fil-ters include dust filter and absolute filters will preventradioactive dust to enter the inner part of the facility.

3.9 Other rock cavernsRock caverns are also used for cold stores and freezingstores which can be an economic solution especiallybecause of energy savings. In urban areas several carparking facilities have been built as surface space ishighly priced or simply because there is no space elsew-here than underground.


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Figure 3.15. Gas filters in an underground facilityFigure 3.14. Typical blast gate and blast door

4.1 Philosophy for geotechnical investigations

Geotechnical investigations for underground projectsare normally divided into two principally different sche-mes; one such scheme is related to investigations doneprior to the construction works, so called pre-investiga-tions and the other is related to investigations that areexecuted during the construction phase. The main aim ofthe pre-investigations is to provide the base data for thedesign and planning works. Investigations made duringconstruction, for example at the tunnel face aim at pro-viding detailed information as a basis for particulardecisions to be taken. Traditionally, the Norwegian tun-nelling philosophy allowed a relative large extent of thetotal investigations to be done during construction. Inmore recent years, when tunnelling in urban areas andenvironmental sensitive areas, pre-investigations havebeen more emphasized. In the following some mainaspects of the investigation principles will be described,including also examples of typical application of somemain investigation methods.

A research programme has currently been undertaken inNorway, named "Milj- og samfunnstjenlige tunneler",in English a translation might read as "Tunnels to servethe society". One of the first objectives of this program-me was to identify the need of seeking new investigati-on methods, and to developing technically the existingones.

The programme concluded: "Pre-investigations shall bedone with methods and means to ensure that a geotech-nical basis exists sufficient to evaluate the consequencesof running a sub-surface project and establish realisticcost estimates". In sub-surface projects it is importantthat the involved parties have a common understandingof the aims of the pre-investigations and that they areaware of the inevitable risk of not being able to cover allaspects of the geotechnical conditions.

Currently, various methods and means to run pre-investigations exist, and it is quite easy to loose the trackand overdo the level of the pre-investigations. Even anextensive pre-investigation schedule may not necessarilyimprove the confidence of the geotechnical basis, but

would indeed increase its costs significantly. A needmust be identified on a project specific basis to choosemethods and content of the pre-investigations. Thiscould include: prevailing geological conditions, locationof the project, geometrical aspects, complexity of theproject, design stage and finally the Owners require-ment to cost and risk confidence.

Predictability is a key word associated with pre-investi-gations. In Norway we experienced a trend during thenineties with an increased number of projects facingdramatic cost overruns and also negative publicity.Predictability was not good enough, neither for the costestimates nor for the consequences of the tunnellingprocess. This was indeed harming the tunnelling indus-try as a whole. Insufficient geotechnical investigationsmay take its share of this development.

The trend is now more towards utilising the technicallymost developed investigation methods even further. Itseems possible to get more information out of the exis-ting methods, and together with a more dedicated inve-stigation program the predictability may again reach thedesired level.

Still the designers responsibility is to identify the appro-priate level of investigations, as the process of pre-inve-stigations is inevitably costly and the outcome of theindividual investigations may be associated with limita-tions. A typical philosophy in Norway has been thatinvestigations that were expected to provide very limitedprobability of construction cost savings were ruled out.It allows a cost and time effective pre-investigationschedule, although it is linked closely to the particularrisk sharing principle that is applied in Norwegian tun-nelling

Geological mapping will always be the basis for geo-technical design. Normally identification of jointingparameters must supplement ordinary geologicalmapping.

The geotechnical design has sometimes been madeflexible and more investigations and detailed design hasbeen made when an access has been made into the area

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4 GEOTECHNICAL INVESTIGATIONS

in concern. This was for example the case for theSvartisen Hydroelectric power scheme near the ArcticCircle in Northern Norway. By the time the 800m longaccess tunnel reached the planned area for the powerhouse area, a water bearing zone was encountered. Coredrilling was then carried out from the tunnel and thedetailed location of the power house was based on thefindings from these borings.

Design procedure according to Handbook 021The geotechnical design for underground tunnel pro-jects typically follows the procedure as outlined below,in accordance with the guidelines in Handbook 021issued by the Public Road Administration.

4.2 Typical investigations at variousdesign stages

4.2.1 Feasibility studyDuring the first step of a project various alignments andlayouts are considered. The investigations are often limi-ted at this stage of the design, and the aim would be todetermine the feasibility of a project and how this can beaccomplished within reasonable costs. The geotechnicalinvestigations typically consist of and report the outco-me of: Desk study of existing geological references, maps and

publications. Study of air-photos A field survey

4.2.2 Detailed feasibility designThe recommendations from the feasibility study are fur-ther detailed at this stage. The final location for the tun-nel is usually selected for further planning. The geo-technical investigations typically employ the followingmain aspects: Registration of soil types and estimation of thickness Mapping of rock types Measuring of bedding and foliation orientation Description and characterisation of jointing Mapping of weakness zones Evaluation of tunnel entrances Geophysical measurements and sounding in areas of

low rock cover Laboratory testing (rock mechanical parameters, dril-

lability tests etc)

Based on these investigations the final location wouldbe determined and the project cost estimate shall be cal-culated with an accuracy of 25%.

4.2.3 Detailed designDuring this stage the chosen project area is evaluated indetail. The geotechnical investigations depend on thelocal conditions and the extent and content of investiga-tions carried out at the detailed feasibility stage.Supplementary investigations would be undertakenaiming at obtaining additional information of particulargeological features, certain areas of a site, etc. The detai-led design would typically include the following: Core drilling Stress measurements Geophysical tomography in particular zones Perhaps numerical modelling

The cost estimate shall be calculated with an accuracy of 10 %

4.2.4 Tender stageThe tunnelling tenders are always supplied with a geo-technical summary report. The geotechnical summaryreport contains a wrap-up of the geotechnical investiga-tions that have been undertaken for the project. Thereport shall also include all factual data that has beenfound during the pre-investigations and describe thegeotechnical conditions expected to be encounteredduring the tunnelling.

4.2.5 Investigations during constructionGeological conditions may be very complex, and it isalways an inherent risk that geotechnical investigationsperformed from the surface have not revealed all detailsof the rock mass. Further, as described above, theNorwegian tunnelling philosophy is a rather flexible oneand certain investigations might serve the projects bestbeing undertaken during the construction stage. Themost typical of investigations performed during con-struction is probe drilling. Further, various geophysicalmethods have been developed for rock mass predictionahead of the tunnel face.

Experienced engineering geologists are normally follo-wing the tunnelling projects conducting geological map-ping underway. This mapping may not serve only as as-built documentation, rather is it also used for forwardprediction of the ground conditions. Particularly suchmapping is useful when it is used together with geologi-cal models and predictions from the pre-investigationsand the geological models are questioned and revisedaccording to new findings. Such models are then usefultools for the contractors and owners for production plan-ning, cost adjustments, etc.


20

4.3 Rock stress and deformation measurements for design and stability control

4.3.1 IntroductionHistorically, few specific geological requirements wereput forward as prerequisite when planning an under-ground project. The rock conditions were often fairlygood, and the site was in many cases more or less fixed.The design was based on standard engineering geologi-cal mapping and experience according to expected andexperienced conditions. Hardly any measurements werecarried out for stability control. However, as large spanexcavations became common, particularly in connectionwith near surface underground sports halls, the need formore accurate stability control measures became moreapparent.

Also, experiences from the mining industry showednumerous cases where excavations with extremely largespan (60 80m and more) were apparently stable wit-hout any rock support at all. Research showed that onemain reason for this was the existence of sufficienttectonic, horizontal stresses even at shallow depths. Pre-dominant horizontal stresses produce favourable com-pression and confinement in the excavation crowns,creating stable self supporting structures.

This called for in-situ rock stress measurementspreferably before the excavation started, followed byrock stress control and deformation measurementsduring and after excavation.

This has been carried out in connection with a numberof large underground excavations to document the stabi-lity of large spans and rock pillars.

Horizontal stresses of geological origin (tectonic stres-ses) are quite common in Norway, and in many cases thehorizontal stresses are higher than the vertical stresses,even at depths greater than 1 000m. The majority of rockstress related problems in Norway actually originatesfrom high horizontal stresses, rather than vertical stressdue to the rock overburden. This has been the case in anumber of road tunnels and tunnels connected to hydro-power development, and high stresses have also causedconsiderable stability problems in power house caverns.This has again called for rock stress and displacementmeasurements.

4.3.2 Applied field methodsRock stress measurementsPrincipally two different principle methods are employed: 2-D ("doorstopper") and 3-D over-coring cells. The

principles are shown in Figures 4.1 and 4.2. Hydraulic fracturing. The principle is shown in Figure

4.3.


21

Figure 4.1. Principle for 2-D ("Doorstopper") overcoringmethod for rock stress measurement

Deformation measurementsDeformation measurements may principally be carriedout in two different ways: Borehole extensometer measurements. The principle is

shown in Figure 4.4. Convergence measurements. The principle is shown in

Figure 4.5.


22

Figure 4.2. Principle 3-D overcoring method for in-situ rockstress measurement

Figure 4.3. Principle for hydraulic fracturing

In addition to this, high accuracy surveying instrumentsmay be used for deformation measurements.


23

Figure 4.4. Principle for borehole extensometer measure-ments.

Figure 4.5. Convergence measurements in a tunnel

Research, development

and consulting

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geology, hydrogeology and environmental geotechnology.

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analysis, and instrumentation and monitoring.

NGI serves the following market sectors:

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25

5.1 Objectives of rock mass classificati-on systems in Norwegian tunnelling

A typical Norwegian tunnel is characterised by chang-ing ground conditions, varying sections of good rockmass quality and sections of poorer quality. The prima-ry objective of the use of rock mass classification sys-tems is thus to qualify various engineering properties of,or related to, the rock mass. The classification systempredominately used in Norwegian tunnelling is the Q-system, whilst others, such as RMR, RMi and GSI areused in few cases.

The output obtained from rock mass classification sys-tems is typically related to:1. Description of the rock mass expressed as quantified

rock mass quality, incorporating the effects of diffe-rent geological parameters. This enables the compari-son of rock mass conditions throughout the site anddelineation of regions of the rock mass from 'verygood' to 'very poor', thus providing a map of rockmass quality boundaries.

2. Empirical design with support guidelines compatiblewith tunnel stability and excavation method.Traditionally, this is often seen as the major benefitfrom the use of rock mass classification systems.

3. Estimates of rock mass properties. Rock mass classi-fication expressed as an overall rock mass quality hasbeen found useful for estimating the in situ modulusof rock mass deformability and the rock massstrength to be used in different types of design calcu-lations.

The classification systems also serve as checklists forgeotechnical field- and tunnel mapping and for core log-ging.

5.2 The Q-methodThe Q-system was developed by the NorwegianGeotechnical Institute in the early 1970s (Barton et al.1974) and has earned recognition around the world. Amajor update was released in 1993 (Barton andGrimstad 1993), and a new update including a completeusers handbook will be released in 2004. The Q-valuecan be calculated as follows:

RQD = degree of jointing (Rock QualityDesignation)

Jn = number for joint setsJr = joint roughness numberJa = joint alteration numberJw = joint water reduction factorSRF = Stress Reduction Factor

The Q-system contains the experience obtained frommore than 1000 case histories from existing tunnels, andan empirically based diagram showing the connectionbetween Q-values and the support used in these caseshas been constructed, see Figure 5.1. The diagram alsoincludes Reinforced Ribs of Sprayed Concrete, a designwhich is partly based on numerical modelling.

5 ROCK MASS CLASSIFICATION

SRF

J

J

J

J

RQDQ w

a

r

n

=


26

5.3 The RMi systemThe RMi sytem has been developed primarily for impro-ving the collection and use of geological parameters inrock engineering. The rock mass index, RMi, is a volumetric parameterindicating the approximate uniaxial compressivestrength of a rock mass. The RMi system was first pre-sented by Palmstrm (1995) and have since been furtherdeveloped and presented in several papers. It makes useof the uniaxial compressive strength of intact rock (sc)and the reducing effect of the joints penetrating the rock(JP) given as:1. RMi = c x JP for jointed rock masses. The jointing

parameter (JP) is by empirical relations connected tothe joint condition factor, jC, and the block volume,Vb. The joint condition, jC, can be estimated by thejoint roughness, the joint alteration (similar to Jr andJa in the Q-system) and the joint size.

2. RMi = c x fs for massive rock having block size lar-ger than approx. 5m3 (where f > JP). The massivityparameter, f , represents the scale effect of the uni-axial compressive strength (which from intact rocksamples to massive rock has a value of approximate-ly f 0.5).

The connection between the different inputs parametersapplied in the RMi is shown in Figure 5.2.

Figure 5.1. Q-values and support guidelines. (Grimstad et al 2002)


27

The different input parameters can be determined bycommonly used measurements and mapping and fromempirical relationships presented by Palmstrm (2000).It requires more calculation than the Q-system andRMR system, but spreadsheets can be used to derive theRMi value.

Based on a characterisation of the rock mass by RMi,combined with geometrical features of the opening andground factors like rock stresses, different rock engine-ering issues such as relevant rock support can be esti-mated using support charts. The charts have been deve-loped from experience of more than 25 different projectsand locations. Possible use of the system is shown inFigure 5.3.

5.4 Experience on the use of rock massclassification systems

A major contribution of the classification systems foruse in underground tunnelling is that they provide a wayof quantifying the quality and capability of the rockmass, which can be understood in a global context. Theirexactness is not of interest in decimals. With careful andrespectful application we have learned in Norway thatsuch systems serve as useful tools both in design andconstruction. Being used in combination with otherclassification systems and together with; engineeringjudgement; analytical and numerical analysis, monito-ring and observation of the tunnel behaviour, the tunnel-ling engineer has a powerful toolbox at hand. It is impor-tant to keep in mind that the appropriate application ofthese systems, both during the design and constructionphases are when they are being considered as guidelinesand recommendations. Site specific considerations andmodifications are needed to enable the most appropriateapplication of any of these classification systems.

It is important to keep in mind that the classificationsystems have some limitations. The systems characterisethe rock mass stability, but not the stability of individualblocks. That means that even in rock mass where thesystem states good stability, individual blocks may beunstable. Concerning the Q-system it must be stated thatmost of the case histories are from hard rocks inScandinavia. In soft rocks, other methods such as defor-mations measurements and numerical modelling shouldbe used in addition.

The systems are often used for other applications thanrock mass stability, such as calculation of different rockmechanical parameters. The results from such calcu-lations should only be considered as rough estimates.However, since it is often difficult to carry out exactfield measurements of such parameters, calculations byusing the classification systems are often the bestassessments the rock engineers can perform.

JOINT ROUGHNESSFACTOR (jR)

JOINT SIZE FACTOR (jL)

JOINT ALTERATIONFACTOR (jA)

JOINT CONDITIONFACTOR

jC = jL x jR/jA

BLOCK VOLUMEVb

JOINTINGPARAMETER

JP

ROCK MASS INDEX

RMi

INTACT ROCK

UNIAXIALCOMPRESSIVE

STRENGTH

c

JOINT SPACINGSor

NUMBER OF JOINTS

Figure 5.2. The input parameters to RMi (from Palmstrm,1996)

Figure 5.3. Possible applications of RMi (from Palmstrm,1996)

Deformationmodulus of

rock masses

Q - system

RMR system

NATM

Groundresponse

curves

Hoek-Brown failure

criterion

TBM progress

evaluations

Numericalmodelling

Communication

Stability androck supportassessments

Fragmentation

and blasting

Rock Mass index (RMi)

applications developed

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UNDERGROUNDCONSTRUCTIONTECHNOLOGY

www.norplan.com

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6.1 GeneralThe ground conditions in Norway can be said to favourthe utilization of tunnelling and underground solutionsand the rock support philosophy reflects this situationwith a flexible rock support application. However, therock mass quality may change rapidly, and contractorsmust therefore be prepared for support of rock mass ofpoor quality also, having the right measures and proce-dures at hand to handle these. A cost effective tunnellingphilosophy has been developed where the application ofwell proven, flexible support systems have played animportant role (Grv 2001). In this chapter the mostcommonly used rock support will be presented.

In Norway, as in many other tunnelling nations, the rocksupport is usually installed in two stages: the temporaryrock support and the permanent rock support. The tem-porary support shall primarily ensure the provision of asafe working environment during the constructionperiod, and is consequently the contractors responsi-bility. The permanent support shall ensure the projectrequirements on long term durability and in principle beintact during the whole lifetime of the tunnel, which forexample is 50 years for road tunnels. The permanentsupport is thus the clients responsibility. A typicalNorwegian speciality, and an important part of theNorwegian tunnelling philosophy, is to combine thetemporary and the permanent support allowing the tem-porary support to later form a part of the permanentsupport. This implies, however, that the material used inthe temporary support must comply with the technicalspecifications as set forth for the permanent support.

The rock support design is often carried out in co-operation between the contractor and the client. Thedesign of permanent support is usually determined bythe client, based on his engineering geological mappingin the tunnel.

Another aspect worthwhile to mention is the applicationof careful observation of the tunnel during the wholeconstruction period. If needed, convergence pins orextensometers are installed for documentation purposes.Any sign of deformation, cracking of sprayed concrete

etc. may indicate that additional support is needed. Witha flexible contract system (and support system) based onthe use of rock bolts and sprayed concrete as needed,additional support can be installed at any time duringthe construction period.

6.2 Rock boltsRock bolts and sprayed concrete are the basic supportmeans in Norwegian tunnelling. Such rock bolts com-prise steel rebar bolts with different types of anchoringmethods. Traditionally, rock bolts with end anchoring byan expansion shell have been used for temporary sup-port whilst rock bolts fully embedded by cement groutare used for permanent support. Recently, rock boltsend-anchored by resin capsules have become widelypopular in the tunnelling industry and these are nowapproved for permanent support, having documented 30years of successful operation. A fundamental investiga-tion of rock bolts is given by Stjern, 1995. One ofStjerns main conclusions is that the fully grouted rebarbolt is considered to be the optimal bolt for hard rockapplications, except for ground where large rock stressinduced deformations are expected. In particular undershear loading where the fully grouted bolt is supersedingthe point anchored and the friction bolt by its instan-taneous high strength dowel effect.

About 250 000 rock bolts are used in Norway each year,most of them for tunnel support. The long term durabi-lity of bolts is an important parameter, and much re-search has been carried out for example by theNorwegian Public Road Administration and the mainproducers of bolts. Generally fully grouted rebar boltshave been considered to be the most durable product.These are mainly applied as hot-dip galvanized forcorrosion protection, a type of bolt that is generally thestandard type in any underground project. The combi-coat corrosion protection has shown to be very effectiveas it consists of epoxy powder coating additional to hot-dip galvanizing. This reliable corrosion protection hasbeen applied in harsh environments, including exposureto salinity and exhaust fumes in sub-sea road tunnels.

6 TUNNEL SUPPORT


30

The newest bolt type on the market is the CT-bolt (seeFigure 6.1), which consists of a steel rebar bolt with anordinary expansion shell (for instant support) and anarrangement for injection of cement. The CT-bolts canthen first be used as an ordinary end-anchored bolt fortemporary support and later on be grouted to a perma-nent bolt. This bolt is available in the market both as hot-dip galvanized as well as combi-coated.

6.3 Sprayed concrete and reinforcedribs of sprayed concrete (RRS)

6.3.1 Application of sprayed concreteIf the block size is too small to be anchored by rockbolts, sprayed concrete would be the preferable supportmethod. Sprayed concrete was introduced for rock sup-port application in Norwegian tunnels in the 1960s.However, the method did not gain any widespread popu-larity until 1980. During the last two decades the met-hod has faced a significant improvement and today,sprayed concrete in Norway is performed in accordancewith the wet-mix method and as fibre reinforced.General technical specifications and guidelines for usein sprayed concrete have been established by theNorwegian Concrete Association, and published in 1999as Publication no.7 (revised in 2003, but only inNorwegian).

The Norwegian Public Road Administration initiated in1995, due to the dramatic increase and the systematicuse of sprayed concrete as rock support, a comprehensi-ve project to document Norwegian experience: "Properuse of sprayed concrete in tunnels."

One of the main conclusions from this project was thatthe production process itself and the application proce-dure of sprayed concrete could dramatically influencethe durability of the final product as well as the supportstructure. This effect must be given special attention inany process aiming at reaching a highly durable product.

Another output from the project was related to the thick-ness of the applied sprayed concrete. It was found that agoverning parameter for durability seemed to be relatedto the applied thickness, and a minimum thickness of60mm has since been required for Norwegian road tun-nels. Any major water leakage must of course be drainedbefore application of sprayed concrete commences.

The study focused the following aspects of with respectto sprayed concrete durability:

a) In urban areas tunnel entrance zones are exposed toaggressive loads during the winter, for example icyroads lead to use of de-icing salts. Thus, the entrancezones in 8 main road tunnels, all opened in the period1970-1992, were studied. Measurements performed onconcrete and sprayed concrete linings in the Oslo areashowed the depth of deterioration is usually less than10mm.

b) Deterioration of concrete structures takes place resul-ting from freezing and thawing processes. Zones expo-sed to such processes were studied in 22 tunnels openedbetween 1956 and 1992. Signs of deterioration haveonly been seen in areas of water bearing rocks with sub-sequent de-lamination between rock and concrete layer.This de-lamination is predominately occurring intunnels older than 20 years with thin layers of sprayedconcrete (less than 20mm).

c) Tunnels crossing underneath fjords and sounds areexposed to extremely harsh environment; saline water incombination with exhaust fumes. 13 sub-sea tunnelsopened in the period 1987 1992 were studied. Since1996 the applied sprayed concrete quality for sub-seatunnels has been C45 and environmental class MediumAggressive. The study showed few signs of deteriorationin these cases. Investigations of the older applications,however, indicated a change of quality in areas withsignificant water seepage.

d) The influence on the sprayed concrete by rockspalling and rock burst was included in the program. 17tunnels from the period 1960-1994 with rock spallingand / or rock burst, were studied. Stress measurementsperformed in two tunnels showed that the stress level inthe fibre reinforced sprayed concrete layer was nearlyzero, and the main function of the sprayed concrete is tostabilize rock particles in order to maintain the self-carrying capacity of the rock mass.

Figure 6.1. CT-bolt

arrangement for grouting

expansion shell for end-anchoring

rotation spring for resin end-anchoring


31

6.3.2 Reinforced ribs of sprayed concrete, descriptionand examplesWhen the Q-value falls below 1, bolting as a supportmeasure may not be adequate on its own, see Figure 5.1.The rock mass between the bolts must be stabilised bymeans such as sprayed concrete. Reinforced ribs ofsprayed concrete is one solution which has become anuseful application in adverse rock mass conditions. Itconsists of a sandwich type construction, based on fibrereinforced (and also plain) sprayed concrete, radialbolts, and rebars (Grv 2000). Figure 6.2 shows a prin-cipal solution of reinforced ribs of sprayed concrete andFigure 6.3 shows an example from a railway station.

The system has the following advantages: Materials to be used are normally available on most

construction sites. Convenient construction, easy to handle materials, and

on-site production. Flexible installation and wide span in capacity. Cost effective. Ductile, allowing rock deformations without imposing

load concentration on support. Allows tunnel progress shortly after installation. Easy to repair and custom design by spraying thicker

concrete or adding new ribs.

For the Bjory sub-sea road tunnel outside Bergen inwestern Norway, the tunnel encountered a zone of loosesilty sand over a distance of 25m (Aagaard et al. 1999).The Q-values in the critical section ranged from 0.08 to0.003. The zone was successfully passed with a designincluding pre-grouting, pre-bolting (spiling), fibre rein-

forced sprayed concrete, and radial bolts. The invert wassupported with a cast-in-place concrete lining. A moni-toring program was established to follow-up potentialdeformations. The monitoring confirmed a stable situa-tion without long term deformations. Despite the stabi-lity of the situation, the tunnel owner, the NPRA,required the rock support to withstand full hydrostaticpressure, which at this particular point was approxima-tely 80m, requiring a concrete cast-in-place lining to beinstalled.

The Frya-tunnel outside Trondheim faced a number ofweak zones during the course of excavation. Rock sup-port covered a wide range of measures from rock boltsand sprayed concrete to cast-in-place concrete. Theeffectiveness of various support solutions has beendemonstrated by the use of numerical modelling(UDEC) for a relatively wide zone with an average Q-value of 0.0013, i.e. extremely poor rock (Bhasin et al.1999). In Table 6.1, a summary of the results fromnumerical modelling is given.

Figure 6.2. Principal sketch of two reinforced ribs of sprayedconcrete with one layer of reinforcement (Grimstad et al 2002)

Sfr

i i i i i i

Cross bars16mm diam.Rebar steel

Sfr

Rock bolt

i i i i i iS S

Sfr

Figure 6.3. Reinforced ribs of sprayed concrete atNationaltheateret railway station

Type of Support Sprayed concrete 250 mm, concrete invert, rock bolts

Reinforced ribs and sprayed concrete (RRS)

Cast-in-place concrete lining (CCA)

Max. Displacement after equlibr. 14.4mm 17.1mm 17.3mm

Max. axial loading on bolts 3.3tons 11.6tons -

Max. axial load on the structure 1.96MN (crown) 0.88MN (crown) 1.4MN (crown)

Max. joint aperture 3.3mm 3.3mm 3.5mm

Max. shear displacement 10.7mm 10.7mm 11.7mm

Table 6.1. Results from numerical modelling (UDEC)


32

FLAC 3D numerical modelling has also been performedto analyse reinforced ribs for the same reinforcementschemes and rock mass conditions as described above.The results confirm earlier calculations indicating thatthe two methods (reinforced ribs with sprayed concreteand cast-in-place concrete lining) produced deformati-ons with insignificant difference where a concrete invertwas applied in both cases.

A cost comparison of various support measures foradverse rock mass conditions is provided in Figure 6.4,including reinforced ribs and sprayed concrete compa-red to cast-in-place concrete lining. One US dollar isequivalent to approximately 7 NOK. A comparison ofthe costs associated with the solution involving reinfor-ced ribs of sprayed concrete with traditional cast-in-place concrete yields that for rock mass classified as1>Q>0.001, the application involving reinforced ribs isthe most cost-effective.

6.3.3 Alkalifree acceleratorCompared to traditional sprayed concrete accelerators,alkali free accelerators offer a final strength increase; byforming a homogeneous and compact concrete matrixwithout internal tension and micro-cracking. Traditionalaccelerators produce a loss of 15-50% in potential com-pressive strength. The various types of alkali-free acce-lerators on the market can provide the following selecti-on of characteristic properties for sprayed concrete: Early strength of 1MPa after 1 hour of curing. Final strength reaching as a minimum the same level

as without accelerator (some produces 20% increaseaccording to the suppliers).

Low rebound.

300mm thickness sprayed in one operation. Low corrosiveness. Reduced permeability.

The Norwegian Public Roads Administration has per-formed a full scale test on a number of alkali-free acce-lerators currently available in the market (Stors et al.1999). The results can be summarised as follows: No difference in personal dust exposure between the

alkali-free and silicate based accelerators. Improved early strength development for the alkali-

free accelerators compared to water glass. Wet conditions at spraying surfaces delay the early

strength development for some accelerators. The tests indicate a durable, homogenous final pro-

duct.

Figure 6.4. Cost comparison of applicable methods

Figure 6.5. Excamples of strength developments using 7%Meyco SA 160


33

In northern Norway, the construction of the FATIMA-tun-nel encountered severe rock conditions forcing the imple-mentation of a cast-in-place concrete lining. A sedimen-tary rock type consisting of shale, siltstone, schist andsandstone hampered progress. Clay-fillings, slickensidedjoint surfaces, and a rock consisting of "chips" in generalless than 5 cm long (and occasionally up to 20 cm) wascommon. The rock mass was in general classified as 0.05< Q < 0.1 equivalent to "extremely poor" to "very poor"rock mass according to the Q-system.

After a successful testing period, sprayed concretelining, with a thickness of 200 to 250mm and alkali-freeliquid accelerator was established replacing the previouscast-in-place concrete lining. Half the thickness wassprayed immediately after mucking out, the remainderafter the next blast round, to allow some deformation totake place. Rock bolts (0.25 bolts per m2) were installedsome 3-5 days after the completion of concrete spraying.

A monitoring program has been implemented consistingof convergence measurements. Almost six months afterthe support installation, deformations in the magnitudeof 1mm/month took place. However, the best indicatorof the behaviour of the support measures is the presen-ce of visual cracking or damage on the sprayed concre-te, of which there has been none reported.

6.3.4 Drained support structureAnother important aspect of the support system descri-bed herein is that the rock mass in combination with therock support constitutes a drained structure. This meansthat the support measure installed has not been con-structed to withstand external water pressure. Excessivewater must therefore not be allowed to build up pressu-re behind the rock support measure.

However, even in a tunnel that has been subject to anextensive, customized pre-grouting schedule, some see-page may occur. This tunnelling concept includes a con-trolled handling of excessive water at the tunnel perip-hery and behind the sprayed concrete lining. Excessivewater must either be piped to the water collection sys-tem in the tunnel or taken care of by a water protectionsystem. Drainage can be achieved by means of instal-ling, for example, local collection devices to confine thewater and transfer it via pipes to the drainage system inthe tunnel (Grv 2001).

Application of sprayed concrete shall not take place inareas of large water inflow until an appropriate drainagehas been applied. This restriction has three purposes; toavoid water pressure being built up behind the sprayedconcrete, to ensure proper bond between the rock surfa-ce and the sprayed concrete, and to avoid dilution of theconcrete as water seep through.

6.4 Ground freezingGround freezing can be used by civil and mining engin-eers to stabilize the ground and control the groundwa-ter while negotiating adverse rock mass conditionsoccurring in weakness zones. The frozen ground provi-des structural support and excludes transport of ground-water on a temporary basis until the permanent supportstructures are put in place. Ground freezing is today acontrollable process. Modern technology and calculati-on programs enable accurate predictions of the progressof the freezing, time consumption, power consumptionetc. The method preserves the ground water level, isenvironmentally friendly, and has proved to be the mostcost effective method in many cases.

To lower the temperature of the ground, freeze pipes areinstalled, usually in drilled holes.

The traditional freezing methods are brine freezing andnitrogen freezing. Brine freezing makes use of a con-ventional freezing plant. The brine is chilled in the free-zing plant and circulated in the freezing pipes where itabsorbs heat from the ground before it is returned to theplant for re-chilling. Typical brine temperature is betwe-en 20C and 40C. Nitrogen freezing makes use ofliquid nitrogen, which is extracted from air. The freezepipes are fed with liquid nitrogen, 196 C at 1 atm. thatevaporates in the pipes and are released back to theatmosphere. Frozen ground gets almost impermeablewhen saturated and frozen. Strength is increasing withdecreasing temperature below the freezing point. Designtakes into account that frozen soil has visco-plasticbehaviour. In the Oslofjord subsea tunnel a section withgravel-like material covering one third of the tunnelcross section at a depth of 130m below sea level was fro-zen stable and watertight before the tunnel was excava-ted through the zone by traditional drill and blast tech-nique.

Figure 6.6. Ground freezing in the Oslofjord tunnel

See Appendix 3 for description of the Oslofjord projectand relevant articles on ground freezing.


34

Figure 6.7. Ground freezing in the Festnings tunnel

35

7.1 IntroductionIn Norwegian tunnelling, application of conventionalDrill and Blast technology is characterized as beinghighly mechanized and requiring a minimum of manpo-wer. Sprayed concrete technology developed during thelast 30 years has revolutionised the rock support andconstitutes an essential part of the current drill and blastconcept.

7.2 State-of-the-art excavation technology

Most civil construction contracts in Norway are unit ratecontracts based on Bill of Quantity for relevant supportand excavation elements. The contractor has to adapt torapid changes, and the decision making process is dele-gated to the tunnel site. The state-of-the-art drill andblast technique in Norway is characterized by the use ofmodern equipment and highly skilled and independentworkers. The shift supervisor and the shift leader toget-her with the clients resident engineer handle the dailytunnelling matters.

In Norway today, most underground excavation takesplace using wheel-bound equipment, utilizing flexibleand mobile units. Very seldom, and mainly in particularexcavations, rail-mounted equipment is used. The bene-fits of a larger tunnel cross-section allow the fasterwheel-bound equipment thus reducing the constructiontime, is often overcoming the additional costs associatedwith blasting and supporting a larger cross-section.

Typical standard equipment used during tunnelconstruction is: Computerized drill jumbos. Each drill machine is

capable of drilling up to 3m per minute. The computercontrolled drilling performance, automatically per-forms alignment for the next round and surveying ofthe previous excavated profile.

Mucking is performed by wheel loader and trucks.Diesel/electric loading equipment is applied for impro-ved environment at the tunnel face.

Support is performed by highly automated and comp-uterized robots for sprayed concrete whilst drilling forrock bolts is mainly done by the drill jumbo. Scalingis normally performed by use of hydraulic hammersmounted on excavators, but still final scaling by hand-held bars is common.

Rock mass grouting takes place using computerizedunits that can deliver grout to several grout holessimultaneously.

The work force in the tunnel has been reduced over thelast years and one person will perform various tasks.Typically the following applies for a Norwegian tunnel-ling crew: The shift crew consists of a shift supervisor and maxi-

mum three tunnel workers at the face; one driller (theleader), one mechanic and one charger. In addition 1-2workers for mechanical repair, service facilities andmaintenance etc.

The operator of the sprayed concrete robot could beone of the workers at the face, but in many cases thiswork is subcontracted to specialised companies.

The wheel loader for mucking out is normally opera-ted by one of the crew members, while the transporta-tion is subcontracted.

The number of trucks needed depends on the nature ofthe project; transport length, cross section etc. Thetemporary road inside the tunnel is often paved inorder to increase the transport speed of the trucks andreduce interference with maintenance work that couldhamper the excavation progress.

Service works such as installation and maintenance ofthe ventilation duct, the water and air supply, etc, isnormally performed by one of the workers from thetunnel crew and an additional operator.

A chief mechanic and the mechanic working in thetunnel perform heavy maintenance in the tunnel or theworkshop. In addition, vendors and suppliers are oftencontracted to perform maintenance, service and followup of the equipment.

The surveyor may not be a full time job, but is oftenintegrated in the work of the QA/ QC department. Hewill normally also perform some of the quantity sur-veying.

7 DRILL AND BLAST


36

This specialization has become possible due to the gene-ral high education level in Norway, where for instance adriller has to be fully trained in the use of computers andthe surveyor has to operate advanced computer soft-ware.

7.3 State-ofthe-art equipmentThe most important equipment related to modernNorwegian drill and blast techniques are the drill jumboand the robot for sprayed concrete. The need for machi-nes that allows for a higher excavation rate has been dri-ven by the need to reduce the construction time, mainlycaused by high indirect cost, or strict demands from theowner.

The jumbo is equipped with a closed cabin for a singleoperator and it is fully automated. After placing thejumbo at its position close to the tunnel face, it is able toposition itself and detect the correct tunnel chainage.When the chainage is detected, the computer retrievesthe drill pattern from the pre-programmed tunnel designand starts to drill the complete round, without any inter-ference by the operator. A laser based surveying equip-ment is installed on the jumbo and during the drilling of

the next round, the surface of the previous round is chec-ked to control that the correct cross section is achieved.On one of the onboard data screens the operator mayverify if there is any need for corrections to be made.The data is transferred to the QA/ QC department forfollow-up. The drill rod length has seen a tendencytowards increased length e.g. 20 feet, but today the com-monly used length is 18 feet.

One single person operates the robot for sprayed conc-rete and it is equipped with a high capacity concretepump and accelerator tanks. The theoretical capacity isnormally 20m3 per hour and the remote operated armwith the nozzle has a length of approximately 10m. Thisallows the operator to be placed in a cabin with a goodview of the working area, or, if needed he can operatethe robot from the tunnel floor. The robot is normallymounted on a chassis from a standard 3.5-7tons truckand will move from site to site as any truck on the road.The ready wet mix is delivered in standard transmixerswith a drum capacity of 6-9m3.

Figure 7.1. Modern drilling jumbos

Figure 7.2. Sprayed concrete robot


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7.4 Drill pattern and blasting techniques

The drill pattern in Norwegian underground openings isoften based on parallel cut in combination with largediameter boreholes. The typical length of a round inhi-bits the use of other kinds of cuts.

Furthermore, the computerized drilling equipment ensu-res reduced deviation from the theoretical path of eachborehole and hence increased tunnel stability. The incre-ased length of each blast round also reduces the over-break along the tunnel axis due to reduced inclination ofeach arm during drilling. A typical successful blastround in competent rock will display most of the drillholes in the tunnel contour.

Typical specifications for drilling and blasting would be: Tunnel excavation by 18 feet steels rods which produ-

ce a tunnel advance of approximately 4.5 5.0m perblast round (10-20 % reduction in length).

Accuracy of the drilling of the contour holes asfollows; collaring within 0.1m measured from theore-tical drill pattern, and for alignment deviation, maxi-mum 6% of the depth of the hole.

The maximum contour hole distance is 0.7m and thedistance to the next helper row do not exceed 0.9m.

The charging of the contour holes and the helper rownext to the contour is reduced, using specialised pipedexplosive or similar measures to reduce the charging,typically the charging would be 0.25 to 0.45kg/m (78%ANFO by weight).

A general requirement to Norwegian tunnels is that norock should be allowed to protrude inside the theoreticalrock contour.

Blasting techniques are developed according to locallaws and regulation and the requirements from the majorclients. These local conditions are not always easilyexported to other markets as the availability and lawsvary between countries.

Explosives developed in Norway can be divided intofour main components. 1) Explosives used in thecontour holes with reduced energy to reduce overbreakand secondary cracking. 2) High-energy explosives incartridges used to initiate the blast and heavy duty blas-ting where specially designed blasting is required. 3)Low cost bulk explosives based on standard fertilizersor site-sensitised emulusion. 4) Finally, non-electricaldetonators with a highly accurate timing system thatenables a wide division of the blast round.

Todays effect of better accuracy of the drilling processcombined with improved quality on explosives andblasting agents lead to less overbreak and secondarycracking of the rock mass. Better controlled fragmen-tation of the blasted rock is also achieved. Further, theseimprovements have reduced the vibrations caused by theblasting and finally, they enable a smooth tunnel contourto be made. The contractor and the owner both benefitfrom these improvements by reduced construction time,better tunnel stability, reduced project costs and saferworking conditions.

7.5 Typical blast round for a 100m2

cross-sectionBy using modern equipment, it is assumed that around140 holes are needed per blast round for a 100m2 crosssection, which require a total time for drilling, chargingand blasting in the range of 4-5 hours. Ventilation isexpected to take 0.5 hour. Before the tunnel face is safefor starting up mucking out, it is expected that 1 hour isneeded to do the necessary scaling before loading andhauling can start.

Rock bolting takes approximately 1.5 hours. Applicationof sprayed concrete is often done at night time, or duringstandstill in the tunnel excavation, if stand-up timeallows it.

A blast round of 4.5m with a 100m2 cross sectionproduces almost 500m3 (solid rock) inclusive overbre-ak. With a capacity of 190 to 220m3 (solid rock) per hourthe tunnel face can be cleared within 4 hours. Thiswould require loaders such as Cat 988F, Bryt X53 orsimilar equipment and trucks/lorries/semi-trailerscapable of carrying 25 to 35tons.

The time needed to perform one complete blast round of100m2 cross-section yields a total of approximately 12hours, giving typical advance rates of approximately50m per week.

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39

8.1 OverviewA total length of about 260km of tunnels has been boredby TBMs in Norway, with diameters ranging from 2.3mto 8.5m. These tunnels serve various purposes, forexample diversion and transport tunnels for hydro-electric power projects, water supply tunnels, sewertunnels and road tunnels as well. The tunnel boringmachines used in Norway up to today, have all been ofthe Open Hard Rock type TBM.

The very first full face boring in Norway took place in1967, executed by The Norwegian Hydro Power Boardby boring of a 73m long, 1.0m diameter raise at TokkeHydro Electric Project. In the beginning of the 1970s acouple of mines in Norway (Mofjellet and Sulitjelma)acquired equipment for boring of raises with diametersup to 1.8m and length up to approximately 250m.

In 1972, the contractor Jernbeton and the City ofTrondheim entered into the first contract of fullfaceboring of a tunnel in Norway. The contractor leased asecond hand 2.3m diameter TBM with operators from aGerman contractor for boring of a 4.3km long sewertunnel.

Sulitjelma Gruber (a mining company) became the veryfirst owner of a TBM in Scandinavia. In 1974 a 3.15mdiameter Robbins TBM was bought for use on the firsttunnel section (4.5km) of the main sewer system for

Oslo City. Sulitjelma Gruber was the first in the worldto use constant cross section cutter-rings, which broughtthe hard rock tunnel boring technology another stepforward due to increased rate of penetration and reducedcutter costs.

See Appendix 8 for further project descriptions and listof references.

8.2 Probe drilling and pre-groutingOn the Western Oslofjord Regional Sewage Project,nearly 40km of tunnels with diameters ranging from3.0m to 3.5m, comprehensive probe drilling and pre-grouting as well as post-grouting were required in orderto avoid lowering of the water table and prevent damageto the buildings along the tunnel alignment. The drillingof probe-holes and holes for grouting on the first sectionwere carried out by handheld equipment. It was recog-nized that on future similar projects it would be neces-sary to incorporate special equipment for probe drillingand drilling of grout holes on the TBM. For later tunnelcontracts on the same project in 1976 and 1977, theowner made strict requirements for probing and pre-grouting. The contractors had to provide and demonstra-te mechanized equipment and methods for efficientprobing and pre-grouting. This became the most exten-sive probing and grouting program ever executed in con-nection with TBM operations anywhere in the world.

8.3 Prognosis model for TBM boringThe Norwegian University of Science and Technology(NTNU), represented by the department of Departmentof Civil and Transport Engineering, has since the midd-le of the 1970s been a prime force for the TBM methodand for the understanding and development of tunnelboring machines in hard rock. In cooperation with con-tractors, machine suppliers and tunnel owners the uni-versity has used the tunnels as full- scale laboratoriesand has in their project "Hard Rock Tunnel Boring"made a comprehensive collection and systematizing ofboring information, thus developed a prognosis modelfor TBM boring. The prognosis model has formed thebasis for better understanding and planning of full face

8 TBM TUNNELLING

Figure 8.1. Open hard rock TBM


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boring projects and has given the contractors a good toolfor detailed calculation and scheduling for TBMprojects. The model is being used for planning and bidpurposes on several projects abroad. The prognosismodel has been recognized by international consultants,contractors and project owners.

In 1998 the university issued an updated and more com-prehensive report on hard rock tunnel boring. Thisreport (1-98) was prepared by Professor AmundBruland.

8.4 Tunnel boring in hard and massiverock formationsNorway is generally considered to provide some of thetoughest hard rock challenges in the world. With fewexceptions, the first TBM projects in Norway started outin the softer end of the hardness scale, boring in greens-chists, greenstone, shale, limestone, phyllites and micaschists. Later, tunnels in Precambrian rocks, granitesand gneisses have been bored. The breakthrough forhard rock tunnel boring came in the period 1981-1984with the accomplishment of the 8km long, 3.5m diame-ter transfer tunnel in Glommedal at Ulla Frre HydroElectric Project. The area contained massive granite andgneiss formations with up to 210MPa unconfined com-pressive strength. In fact, the rock on this project was somassive, that the NTNU prognosis model was revised toinclude the fracture class 0 (zero). The Robbins TBM117-220 worked for 2.5 years to cut through the massi-ve rock on the 8 022m diversion tunnel. The samemachine has bored a total of 42km of tunnel on fiveprojects, all in hard rock formations.

8.5 High performance TBM In 1988 The Robbins Company introduced incooperation with Statkraft, the High PerformanceTBMs, using 19 inches (483mm) cutters. The three firstHP TBMs ever built, with diameters ranging from 3.5mto 5.0m, bored a total of 34km of tunnels at Trollbergetjob site, Svartisen Hydro Electric Power Project. (Twoother, second hand standard TBMs bored another 23kmof tunnels at the Svartisen Project). By this develop-ment, the cutters, the TBM machine itself and the TBMperformance were taken to a new level, and gave

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