Tunneling in fault zones, Tuzla tunnel, Turkey

Tunnelling and Underground Space Technology 18 (2003) 453465

0886-7798/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0886-7798(03)00045-2

Tunneling in fault zones, Tuzla tunnel, TurkeySuleyman Dalgc*

Faculty of Engineering, Istanbul University, Faculty of Engineering, 34850 Avclar, Istanbul, Turkey

Received 8 August 2002; received in revised form 20 December 2002; accepted 19 February 2003

Abstract

The Tuzla tunnel was excavated mainly in fault zones, shale and limestones using the conventional and shielded tunnel boringmachine (TBM) methods. Fault zones in shales are brecciated and clayey, while those in limestones are of blocky structure. Therock mass rating, rock mass classification and support systems proposed for fault zones in Tuzla tunnel are insufficient forexplaining the deformation and failure mechanisms encountered in the tunnel. In addition, dyke exposures, the fault-collapsedkarstic system and groundwater also caused some problems during the excavation of the tunnel. The most important event relevantto fault zones in the Tuzla tunnel was the selection of a TBM. Before the excavation of the tunnel, the rock was determined tobe of poor to fair quality. Therefore, tunneling with a TBM in rock of poor to fair quality was thought to be economic. However,during the excavation, fault zones with poor to very poor rock characteristics were encountered along an area comprising 70% ofthe tunnel length. The fault zones caused jamming of the TBM cutter and deviation from the tunnel alignment. In this respect,tunneling with the TBM method was quite problematic. Geotechnical problems encountered in the fault zones required specialmeasures to be taken in the tunnel. With these measures, excavation and supporting of the tunnel were completed successfully bytransforming heterogeneous conditions in the fault zones to homogeneous conditions in the tunnel impact area. 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Tunnel boring machine; Fault zones; Rock mass rating

1. Introduction

The Tuzla tunnel, which is about to be completed,has an outer diameter of 5 m, an inner diameter of 4.5m and a total length of 6500 km. The tunnel with asingle tube is built for sewage operations (Fig. 1). Theseexcavations are all shallow with typical depths to thetunnel crown of between 15 and 20 m. The Tuzla tunnelwas excavated in fault zones, shale and limestones.Tunnels opened in shales are generally subjected toswelling, which triggers some mass movements into thetunnel such as collapses and slides (Brattli and Broch,1995; Einstein, 2000). In the Tuzla tunnel under inves-tigation, no swelling was detected in shales, however,fault zones that comprise 70% of the tunnel length wereencountered in the shales.Brittle shear zones observed particularly in shales in

the Tuzla tunnel in the shallow parts of the crust, aregenerally within 510 km of the Earths surface, wheredeformation is dominated by brittle mechanisms, such

*Tel.: q90-212-6763636; fax: q90-212-591-19-97.E-mail address: [email protected] (S. Dalgc).

as fracturing and faulting. Brittle shear zones are, ineffect, fault zones, and they are marked by fault gougeand other rocks of the breccia series (Davis and Reyn-olds, 1996). The brittle rock deformation, such asparticle size reduction by crushing of grains and reorien-tation of grains by shearing, generates the characteristicfine-grained gouge (Scholz, 1990; Twiss and Moore,1992).During the tunnel excavation, some geotechnical

problems were encountered in the fault zones such asinstability of the face, excessive overbreak, excessivedeformation by squeezing andyor swelling fault rocks,instability of construction stages, and excessive waterinflow frequently associated with flowing ground (Ried-muller and Schubert, 2000).In order to evaluate problems encountered in fault

zones in the Tuzla tunnel as well as their solutions, inthis study, data on exploratory wells drilled on the tunnelroute, laboratory studies and observations and measure-ments conducted in the tunnel were utilized. Locationsof boreholes to be drilled on the tunnel route wereselected on the basis of the positions of shaft and tunnels

454 S. Dalgc / Tunnelling and Underground Space Technology 18 (2003) 453465

Fig. 1. Location map of the study area.

and surface structures. A total of 33 boreholes weredrilled on the tunnel route. Boreholes were continued2.2810.44 m from the tunnel elevation. In laboratorywork, samples of lithology on the tunnel route weresubjected to bulk unit weight, uniaxial compressivestrength (UCS), indirect tensile strength and point-load

strength index tests. On the basis of observations madein the tunnel and the results of laboratory tests, rockmass ratings (RMRs) following the RMR system (Bien-iawski, 1989) were made. Using the data obtained, thedrilling works in fault zones, and the estimated andmeasured rock mass values, disadvantages of rock-mass

455S. Dalgc / Tunnelling and Underground Space Technology 18 (2003) 453465

Fig. 2. Geological section of the Tuzla tunnel.

classification, problems arising from dyke rocks, karsticenvironments, effects of groundwater, seismicity, andthe excavation and support properties of conventionaland tunnel boring machine (TBM) methods wereexamined.

2. General geology of the tunnel

The Tuzla tunnel was opened in a limestone and shalelithology of the Istanbul Devonian sequence, which isnamed the Kartal formation (Fig. 2). Along the tunnelroute, there are different types of lithology, such aslimestone and shale alternated with each other, clay andlimestone blocks in karstic limestones and blocky, brec-ciated, clayey material in the fault zones. Shales arestubby and consist of quartz and kaolinitized feldsparwith detritus opaque minerals and sericite. Micriticlimestone levels are medium to thick bedded and havefair to high strength and show sparritic veins. This studyfocuses on the blocky, brecciated, clayey fault zones. Inaddition, recent alluvium deposits and Belgrat formationconsisting of Neogene claystone are also observed alongthe tunnel route. In the present study, detailed featuresof Neogene and quaternary deposits on the tunnel routewere not investigated.Between E and F shafts, the Tuzla tunnel was exca-

vated in alternating shale and limestone. Some parts ofthe tunnel between F and G shafts were excavated inlimestone and some in shale. The top heading of theexcavation face in FG tunnel is dominated by softclays of the Belgrat formation, which also contains rock

fragments probably derived from the bedrock (Ozaydnet al., 1998). As a result of collapsing of clay andlimestones in the karstic environment between the Gand H shafts of the tunnel, the two materials are mixedwith each other and heterogeneous tunnel conditionsappear. The area of the tunnel between the I and X1X2 shafts is generally constructed in shale. Shale levelsare accompanied by a lesser amount of limestone. Dueto faulting, areas of shale are brecciated and clayey,while limestones show a blocky structure.Devonian rock units in the tunnel route have been

affected by Hercynian and Alpine orogenies. Therefore,clayey and brecciated fault zones develop particularlyin shales of the Kartal formation, while foldings andblocky fault zones dominate in limestones. Becauseshale is not resistant to deformation, breaking is commonin areas of limestone and shale alternations, whileconcentric foldings dominate in limestones.During the tunnel excavation works, two different

fault directions were determined. The first group offaults is in the NWSE direction, while the secondgroup has a direction of EW. The faults were deter-mined to be normal faults. In general, the northernblocks of the faults are raised, while the southern blocksare fallen. The crushed zone in the faults is between0.20 and 30 m. Because the tunnel route is in the NSdirection, faults and dykes with a NWSE directionhave more impactcompared to those with an EWdirection.Bedding strikes in the tunnel are generally N40508E

and they dip 30408 to the SW. Bedding surfaces are


Fig. 3. Position of the North Anatolian Fault Zone with respect to tunnel axis.

Table 1Field test results

Tests Limestone Shale Fault zone

Number Max. Mean Number Max. Mean Number Max. Min.of tests of tests of tests

Lugeon test 2 1.94 1.84 5 4.80 2.74 3 1.79 1.50

Pressure-meter testElastic modulus E (MPa)m 8 367.9 261.1 18 250.3 65.53 6 135.4 0.17Limit pressure PI (MPa) 8 )2.4 )2.37 18 )2.4 0.88 6 )2.3 0.07

smooth, slickensided or slightly rough and coated withclay. Limestones are medium to thick bedded (15300cm), but they are on average medium bedded (30 cm).Shales vary from thinly to thickly bedded (0.140 cm),but they are generally thinly bedded (35 cm). Rockquality (rock quality designation, RQD) values observedin drill cores and in situ are 5070% for mediumthickbedded limestones, 040% for laminated shale. Coreefficiency in areas of shale is between 0 and 40%, whileit is 40100% in limestones. On the basis of thesevalues, the core efficiency and rock quality values ofshales are lower than those of limestones. The fact thatshales have low rock quality values and core efficiencyin comparison to limestones is due to the fact that theyare affected from intense tectonism and they are thinbedded or laminated.The Tuzla tunnel is located approximately 5 km north

of the North Anatolian Fault Zone, which is the mostactive fault zone in Turkey (Fig. 3). The North AnatolianFault Zone, extending from the western to the easternpart of Turkey is one of the most important tectonicstructures of the World. The North Anatolian Fault witha right-strike slip character was formed. The NorthAnatolian Fault Zone generally traces the boundaries ofPontide zone, Intra-Pontide zone and Sakarya continent(Sengor, 1979). Because the route of the Tuzla tunnelis to the north of the active faults, fault zones encoun-

tered in the tunnel might have been old faults and havelost their activity.

3. In situ testsIn the field, the Lugeon and pressure-meter tests were

conducted in boreholes. Values obtained from theLugeon test indicate that limestone (1.84 lymys), shale(2.74 lymys) and fault zones (1.50 lymys) are lesspermeable (Table 1). In the Tuzla tunnel, groundwaterwas not detected in the borehole within the shales andlimestones that are classified as less permeable on thebasis of Lugeon values. However, during the tunnelexcavation, groundwater was detected as flowing ordripping in each of the blocky and brecciated faultzones, while it was observed as leakage in the areas offault gouge. In GH tunnels where karstic limestonesare widely exposed a water flow of up to 30 lys wasrecorded. Due to this flow, discharge of spring waters500 m distant from the tunnel axis was diminished. Thepressure-meter test was conducted in situ for determiningelastic modulus and limit pressure (Table 1). The aver-age of the elastic modulus in limestone, shale and faultzones is 3679, 800 and 70 kgycm , respectively.2

4. Laboratory testsLaboratory tests were performed on the specimens

prepared from block samples and borehole core to


Table 2Laboratory test results

Parameters Number Limestone Number Shaleof

Max. Min. Meanof

Max. Min. Meantests tests

Bulk unit weight (kNym )3 20 2.7 2.5 2.6 5 2.5 2.0 2.3Point-load strength index (MPa) 25 9 4.8 7.2 14 2.0 1.2 1.4Indirect tensile strength (MPa) 8 9.0 4.7 6.0 - UCS (MPa) 18 100 55 75 7 52 12 28

Fig. 4. Strengthdeformation relation for limestone and shales.Fig. 5. Effects of structural movements in limestone and shalelithologies.

determine the geomechanical parameters of the intactrock. The tests on NQ size specimens were carried outaccording to the procedures recommended by ISRM(1981) suggested methods (Table 2). In the tests, dif-ferent values were obtained for shale and limestone.This difference is attributed to presence of clay mineralsin shale and their brittle character. Considering thesheardeformation relation for limestone and shale,limestones are elasto-plastic while shales show a brittlebehavior. Fig. 4 also supports that faulting is intense inshales while very limited in limestones.

5. Geological strength index classification

Rock mass properties observed in the excavation ofthe Tuzla tunnel were classified using the geologicalstrength index (GSI) system (Hoek et al., 1998). Bed-rock in the tunnel is blocky, and very blocky when it isnot affected from the faults. In case the bedrock isaffected from the faults, it is blocky, brecciated (disin-tegrated) and clayey (foliatedylaminatedysheared).Approximately 40% of the faulted rocks are classifiedas blocky, 30% brecciated and 30% clayey. Average GSIvalues of this type of faulted rocks are 35"5, 25"5and 15"5, respectively (Fig. 5).Blocky fault zones are formed by many intersecting

discontinuity sets. Clay or brecciated fill is not commonin this type of fault zone. This type of fault zone isdetected every 35 m in the Tuzla excavation. This typeof fault zone is detected in limestones, and block fallsand slides due to gravity are frequently observed.Brecciated fault rocks are a poorly interlocked, heav-

ily broken rock mass with a mixture of angular androunded rock pieces. Fills of this zone are composed of

angular fault breccias with slickensided surfaces. Thistype of fault zone is generally found in alternations ofshale or limestone-shale. Raveling in brecciated zonesand flowing conditions in areas affected by groundwaterare encountered.


Table 3Classification of fault rock mass

Rock mass parameters Blocky Brecciated Clayey

UCS (MPa) 65 7.5 1.0Rating 7 2 0Drill core quality (%) 5070 040 0Rating 13 3 3Spacing of discontinuities 200600 mm 60200 mm -60 mmRating 10 8 5Discontinuity length 310 m 1020 m )20Rating 2 1 0Separation 0.11.0 mm 15 mm )5Rating 4 1 0Roughness Slightly rough Smooth SlickensidedRating 3 1 0Infilling )5 mm -5 mm )5 mmRating 2 2 0Weathering Moderately Highly DecomposedRating 3 1 0Groundwater Dripping Dripping WetRating 4 4 7Strike and dip orientations of discontinuities Unfavorable Unfavorable UnfavorableRating y10 y10 y10

Total Rating 38 13 5Description Poor rock Very poor rock Very poor rock

Table 4Strength parameters of rock mass

Fault zone UCS si Constant Estimated Cohesion Friction Deformation(MPa) Mi GSI mass angle modulus

(MPa) mass (f8) E (MPa)

Blocky 65 11 35"5 2.08 28 3400Brecciated 7.5 8 25"5 0.15 23 640Clayey 1.0 4 15"5 0.10 15 130

Clayey (foliatedylaminatedysheared) fault zones arethinly laminated, tectonically sheared, slickensided andhighly weathered surfaces. Clayey fault zones are gen-erally composed of shale. In limestones, crushing dueto faulting is limited because of the physical andmechanical features of the fault zone. In fault zoneswith clay fill, it is observed that the shallow stresscondition controls shear failures in combination withdiscontinuities and gravity controls the failure of therock mass.

6. Rock mass strength

A strength range was empirically estimated in thefield on the basis of the descriptive classification ofHoek et al. (1998). Based on the measured or estimatedUCS and ranges of material constant (M ) values andiGSI values (Hoek et al., 1998; Morinos and Hoek,2001) attributed to the different rock mass types, thecohesive strength and friction angle for each faultedrock-mass type was estimated for design purposes (Table3).

In addition, using the GSI system, the faulted rockmass deformation modulus E for G -100 MPa ism ciestimated in GPa from the Hoek and Brown equation(1998). On the basis of this equation, MPa values ofblocky fault zones, brecciated fault zones and fault claysare 3400, 640 and 130, respectively. These values areclose to those obtained from the elastic modulus test.Therefore, values calculated from the equation are sup-ported with in situ rock mechanics tests.

7. Rock mass values

On the basis of drilling data, RMR rock mass valuewas determined as fair, poor and very poor rock in someareas. No classification parameter was given for faultzones. RMR values from measurements inside the tunnelare between good rock and very poor rock quality.Detailed RMR rock mass classification, on the basis ofmeasurements and observations conducted on fault rockenvironments inside the tunnel, is given in Table 4. Inthis classification, RMR rock mass classification valuesobtained from bedrock in blocky fault zones indicate a


poor rock mass. RMR values from bedrock in brecciatedfault zones and clayey fault zones are classified as verypoor rock.

8. Evaluations of the fault zones

In Tuzla tunnel, geotechnical problems arising fromthe fault zones are examined with following subtitles:

8.1. Evaluations of drilling data in the fault zones

Fault zones in shales within the Tuzla tunnel couldnot be sufficiently determined with boring because oflow core efficiency and a limited number of boreholes.Likewise, during the limited number of drilling works,fault clays are washed out and the fact that these sectionsmight be a part of fault zone may not be noticed.Therefore, it becomes quite difficult to determine faultzones with a low core efficiency. In addition, strike slipand normal faults as well as dyke structures are in aclose to vertical orientation. Determination of drillingsites on these structures is only possible with finding ofmorphologic data in the topography. In cases such asTuzla tunnel where a very flat topography is occupiedby several residential areas, fault zones could not bedetermined with morphologic data. In this kind ofinvestigation, further information on the rock massproperties could have been obtained by use of downhole cameras, while in some circumstances the use ofinclined boreholes, geophysical surveys and trial shaftswould also have been beneficial (Dalgc, 2000). In thisrespect, there may be pilot tunnel works to be conductedfor finding the fault zones. However, pilot tunnel worksmay disturb the primary stress distribution in the field.In some cases, pilot tunnel works may be beneficial fordrainage of groundwater and predicting of support sys-tems to be applied at these sites and locating fault zonesthat could not be sufficiently determined with drillingstudies.

8.2. Problems arising from dyke rocks in the fault zones

Along the tunnel route, dyke rocks showing geotechn-ical behavior different from the surrounding units couldnot be determined in exploratory boreholes, since theyare extremely altered and soft with a very poor characterand a basic composition. Because these rocks are closelyassociated with tectonic movements and magmatic activ-ities, it is known that they are exposed along the faultzones. On the basis of field observations, dyke rockshave a direction of NWSE that is consistent with mainfault orientations. They also extend in an EW directionalong the dykes. Dyke rocks of basic composition actas clay-filled fault zones. This, in turn, causes excessiveoverbreak, collapsing and deformation risks to occur incontact areas between dyke rocks and the surrounding

units. In such cases, a greater degree of support elements(steel support, wire mesh, shotcrete, invert concrete,etc.) were used in the dyke rocks as in the fault zones.In addition, excavation took a long time along thecontacts from dyke rocks and fault zones to the bedrock.

8.3. Rock mass values in fault zones

Because the fault zones could not be sufficientlydetermined during drilling works in the Tuzla tunnel,rock mass values obtained from drilling data are higherthan those determined in situ. In one of the studiesrelating to determination of rock mass values on thebasis of drilling and tunnel excavation data (Barton,1976), rock mass values obtained from drilling datawere found to be two times higher than those observedduring the tunnel excavation. Bartons data wereobtained from quite massive biotite gneiss. In otherworks (Cameron-Clarke and Budavari, 1981; Loset etal., 1994), rock mass values obtained from drilling datawere found to be lower than those observed during thetunnel excavation which was attributed to the presenceof intense joint systems in contrast to in situ drillingdata.

8.4. Disadvantages of rock mass applications in thefault zones

The RMR rock mass classification for the Tuzla tunnelcannot explain the failure mechanisms encountered. Thisis related to the fact that parameters used in the RMRrock mass classification are insufficient. In addition, ifthe minimum and maximum stress distribution in theRMR rock mass classification system is absent, coupledwith an anisotropic rock mass with varying time-depend-ent behavior, the classification becomes inadequate(Riedmuller and Schubert, 1999). In studies conductedto increase the reliability of rock mass classificationapplications, the following flow chart is recommended(Palmstrom et al., 2001), (Fig. 6). Consideration of thepossible behavior of the ground types is the advantageof this classification.

8.5. Effect of groundwater in fault zones

Groundwater with a discharge rate of 100 lyminissuing from fault zones in the excavation face causessoftening and flowing of fault clays as well as blockfall, rock slide, raveling and flowing processes in brec-ciated and blocky fault fills as a result of loweredcohesion in the fracture surfaces. Therefore, prior toexcavation in fault zones, drainage holes and pipes wereplaced on the face and shotcrete was applied as quicklyas possible. However, stability measurements wereincreased by applying jet grouting in problematic sites.In addition, leakage water in clayey fault zones spread


Fig. 6. Rock mass characterization and classification (Palmstrom et al., 2001).

Fig. 7. Heterogeneous conditions in karstic limestones.

out over the excavation site and caused sinking of theloading machine into the soil and lowered its maneu-vering potential. To counter this, waterproof fill materialwas placed onto the tunnel invert. Water from boreholepumps in front of the face was removed from the site.When fault zones are water saturated, shotcrete is

applied to increase the stability of face. However, theshotcrete may be washed out by the flow of water if itis not hardened yet, and then, these areas need to beshotcreted again. Thus, the amount of shotcrete appliedto the face of water saturated fault zones was approxi-mately 1.0 m . In some cases, accelerating admixtures3were added to the shotcrete and the thickness of shot-crete was increased. In bolt works, the holes openedacted as drainage canals. Injection mortar applied at alater stage may be lost through these areas dependingon the water flux. Therefore, more strict applicationswere made such as adding of accelerating admixtures tothe injection mortar and changing the cementywaterratio in the injection material. During the constructionof the inner lining, groundwater in the blocky andbrecciated fault zones washed out cement mortar fromthe fresh concrete and caused the concrete to becomepermeable in some places.

8.6. Effect of fault zones on karstic environments

In the GH part of the Tuzla tunnel, it was observedthat slide surfaces and fault breccias indicative of faultplanes in old karst system were collapsed due to theshifting of strata in association with faulting. This causeda mixing of clay and limestone blocks, which havedifferent geotechnical features. Therefore, it was notclear when and which type of rock would be encountered

in the tunnel face (Fig. 7). In this case, excavation andsupport systems were continuously changed in the face.In this environment, a so-called mixed face, excavationand support systems became difficult to operate and theprogress rate decreased (Ulker, 1998). Therefore, it isaccepted that soils with different physical characteristicsencountered at the tunnel face is still one of the mostdifficult conditions in todays tunneling sector.

8.7. Seismicity of the fault zone

In a tunnel, there may be some deviation of the tunnelaxis due to active faults andyor collapses in the tunneldue to ground vibrations. These events are controlled


Fig. 8. Section of support system in conventional method.

Table 5Support system in conventional method with respect to RMR system

Application Blocky faulted rock Brecciated faulted rock Clayey faulted rock

Shape Horseshoe Horseshoe CircularAdvance 1.501.75 1.001.25 0.500.75Face supporting body y If required qForepoling y If required qAdvance in top heading 10 m 5 m 3 mSteel sets y q qWire mesh 1 layer 2 layerShotcrete 10 cm 15 cm 20 cmBench support y y qExcavation Drill and blast Drill and blast or machine Machine

primarily by the earthquake acceleration, geotechnicalproperties of rocks in the tunnel, tunnel diameter andsupport systems used in tunnel (Dowding and Rozen,1978). According to Dowding and Rozen (1978), whenthe maximum ground acceleration is less than 0.19 g,no damage is observed in tunnels and when the maxi-mum acceleration is between 0.19 and 0.52 g, a smallamount of damage occurs. If the ground acceleration ishigher than 0.52 g, a significant amount of tunnelcollapse is expected. Two devastating earthquakesoccurred on the North Anatolian Fault Zone during theconstruction of Tuzla tunnel: the 17 August Izmit earth-quake (Ms7.4) with a maximum ground accelerationof 0.350.40 g at the epicenter, and the 12 November1999 Duzce earthquake (Ms7.2) with a maximumground acceleration of 0.6 g at the epicenter. Neitherearthquake had a significant effect on the tunnel. Thefacts were, the ground acceleration at the tunnel axiswas less than 0.52 g, the epicenter locations during theIzmit and Duzce earthquakes were 40 and 180 kmdistant from the tunnel, respectively, the outer and someinner linings of the excavated areas on the tunnel routehad been constructed, the tunnel diameters were rela-tively small and the low primary stress distributionpresent played important roles in the lack of tunneldamage.

8.8. Support and excavation with conventional systemin the fault zones

There are some arguments over flexible and rigidsupport elements applied to tunnels (Riedmuller andSchubert, 2000). Characteristics of flexible systems aregiven by Schubert and Moritz (1998) and Moritz(1999). However, application of flexible support systemsmay be difficult when the primary stress is intense(Dalgc, 2002).In the Tuzla tunnel, since there is no problem relating

to primary stress, support was made with shotcrete, steelarches, wire mesh and rock bolts. The tunnel supportsystem was applied with revisions in accordance to theRMR (Table 5 and Fig. 8). In the later stages of tunnel

excavation, some corrections were made with respect toenvironmental conditions. The distance between thesupports is generally 1.51.0 m. In clayey and brecci-ated fault zones of very poor rock character, spiling andtwo folds of wire mesh were placed and shotcrete wasapplied following the excavation. The thickness ofshotcrete was applied as 20 cm for very poor rockenvironment with clayey and brecciated fill and 15 cmfor a blocky rock environment. In fault zones, in additionto the normal support systems, additional support sys-tems were also used. Additional measures were takenwith jet grouting, a forepole umbrella, drainage, partialface excavation, reduction of number of excavation stepsand resort to face-supporting applications. Among thesesupport systems, rock bolts and forepole umbrella appli-cations yielded successful results in areas where blockyand brecciated fault zones existed. In cases where faultclays dominated, because of the difficulty achieving


Table 6Specifications for the Robbins 165-162yE 1080

Property Values

Machine diameter 5.0 mNumber of cutters 36Rotational speed 6 rpmNormal thrust force 471 tMaximum thrust force 785 tCutting head power 600 hpPower of the miscellaneous pumps, etc. 285 hpConveyor belt capacity 476 m yh3Electrical transformer 1000y380 V to 50 Hz

Fig. 9. The tool configuration of the Robbins TBM.

adequate anchorage, promising results could not beobtained. In areas where rock bolts could not be applied,shotcrete or steel set application were favored. However,shotcrete showed flowing in areas of fault clay due togroundwater, and steel set applications were started. Ina small tunnel like the Tuzla, steel set applications wereperformed with difficulty. The jet grouting methodyielded successful results against softening of fault clayswith water and their flowing over the tunnel face. Inblocky, brecciated fault zones, removal of groundwaterfrom the environment and coating of the face withshotcrete were beneficial for maintaining the stability.Although reducing of the excavation advance step, facesupporting and sequence excavation works in fault zonesgave satisfactory results for tunnel stability; they hadseveral disadvantages in terms of time and labor. Partialface excavation was conducted in clayey and brecciatedfault zones.

8.9. Support and excavation with TBM in the fault zones

On the basis of examinations conducted prior totunnel excavation, as the most reliable and the fastestexcavation method in the X1X2, K1 part of the tunnel,a shielded TBM was selected for shale and limestonewith poorfair rock quality. When making this selection,minimum damage on buildings and industry facilitiesaround the tunnel route was considered. In the Tuzlatunnel, excavation with TBM was carried out with a165-162 model Robbins TBM for a length of 1670 m(the distance between the X1X2, K1 shafts) (Table 6).The rotating head of the machine has 36 discs and thedistance between cutters in the head design of themachine is 7.5 cm. The tool configuration of the cuttinghead is shown in Fig. 9.During the excavation by TBM, limestones were

coated with shotcrete. Steel support used in alternatingshale and limestone with poor to fair quality wassupplemented with wire mesh and shotcrete. Collapsesoccurring in fault zones were filled with shotcrete andgrout injections. In a later stage, these parts weresupported with wire mesh and shotcrete (Fig. 10).

The advantages and disadvantages of tunnels exca-vated with a TBM are explained by Cox (1973),Bougard (1984) and Kovari et al. (1993). According tothese works, the advantages of a TBM are: increasedrate of advance (as a function of rock strength), near-absence of break, smooth and more stable opening,requiring less support, reduced damage at ground sur-face, safer working conditions. The disadvantages of aTBM are high capital cost, lead time for constructingthe TBM; lack of versatility vis-a-vis the ground con-`ditions, expensive replacement for consumable tools,low advance rate in very strong rock or in very poorrock. In the Tuzla tunnel, absence of subsidence throughto the surface was an advantage of a TBM machine.Three occurrences of subsidence did happen in areasexcavated by the classical method. The main disadvan-tages of the areas excavated by TBM were excessiveoverbreak and subsidence observed in very poor rockconditions in shales.In blocky and brecciated fault zones, this event caused

jamming of the TBM cutter and shield and, thus, theexcavation and pushing processes became quite difficult.In spite of all the interventions, the TBM deviated fromtunnel elevation and tunnel axis in clay filled faultzones. In addition, it was also faced with some otherproblems relating to support. Therefore, some labor,time and material were lost in faulted rock environmentsand, as a result, excavation with the TBM was notsuccessful. In this respect, the amount of crushed rocksin fault zones should be carefully examined if a TBMmethod is applied. In the Tuzla tunnel, blocky, brecci-ated, broken and clayey crushed zones above or in front


Fig. 10. Section of support system in tunnel excavated with TBM method.

Table 7The overall TBM performance in Tuzla

Starting date 6 October 1997Finishing date 31 July 1998Length of tunnel 1600 mTBM Diameter 5 mFinal tunnel diameter 4.5 mAverage machine utilization 10%Machine utilization in competent rock 35%Average net cutting rate 50 m yh3Average progress rate 5.1 m yh3Best daily advance 15.2 mydayAverage daily advance 6.2 mydayBest weekly advance 69 myweekAverage weekly advance 33 myweekBest monthly advance 253 mymonthAverage monthly advance 135 mymonthCutter cost 4 $ym3

(Bilgin et al., 1999b). Fig. 11. Geologic conditions affecting daily progress rate with TBM.

of TBM required a change of excavation method. Thissituation was also encountered in the San-Antonio flood-control tunnels (Green and Wallace, 1993). In addition,when subsidence occurred in fault zones of the Tuzlatunnel, the material that accumulated on the shield ofmachine was removed by manpower, and therefore, theprogress rate was extremely low. In this case, excavationwith the conventional method becomes more economicand application of practical additional measures yieldedsatisfactory results. If a TBM is present in the tunnelface, application of additional support systems becomesdifficult.The performance of the TBM and face conditions

were recorded continuously during tunnel excavation

(Table 7). On the basis of Table 7, the expected progressrate was determined as 15 myday. In rock environmentsthat are not much affected from faults, the rate of drilland blast method averages 80 mymonth while it is 135mymonth for the TBM method. Although the TBMaverage of daily realized progress rate was found to be6.2 myday, this value decreased to 0.5 myday in faultzones and some openings were detected on the ceilingof tunnel at these sites (Fig. 11). In fault zones, thedrill and blast progress rate reached 1 myday; this valuewas 2.5 myday in intact rock. These values for drill and


Fig. 12. Relationship between RQD and daily advance rate.

Table 8Comparison of predicted and measured TBM performance values

Tunnel Disc cutting Cutting force (kNydisc) Net cutting rate (m yh)3(km) depth

Predicted Measured Predicted Measured(X1X2, K1) (mm)

172.7 11 91.3 73.9 80 71175.3 7 58.1 69.8 53 49190.2 8 66.4 69.9 61 57194.0 9 75.1 72.3 60 64225.6 7 58.1 59.3 53 49227.9 10 83.0 117.2 70 71251.3 8 66.4 111.2 61 57272.1 11 91.3 123.7 80 71275.4 9 75.1 89.0 60 64275.4 13 107.8 126.2 74 92284.5 8 66.4 96.0 61 57

(Bilgin et al., 1999a).

blast progress rate in fault zones were advantageous butthe opposite was true for intact rock. In addition,relationships between RMR values (Bieniawski, 1989)with daily advance quantity are presented in Fig. 12.The best daily advance (15.2 myday) was reached forRMR 55%. In blocky, brecciated and clayey fault zones,the measured RMR value decreases, leading to adecrease in the excavation advance rate.Eleven different zones in the intact rock were chosen

for in situ observation of the TBM performance in theTuzla tunnel. Special attention was paid to the fact thatthe rock formation in selected zones should have similarmechanical properties with those tested in full scalelaboratory cutting tests (Bilgin et al., 1999b). Predictedand measured values are compared in Table 8. As canbe clearly seen from this table, the predicted values arevery close to actual values. But, these values are notvalid in the fault zones. For this reason, in fault zones,TBM performance should be based on rock mass clas-sification because the physical and mechanical propertiesdetermined in the laboratory are not representative inthe fault zones.Furthermore, it is important to note that the full

performance of a TBM or daily advance rate is a

complex matter, which is mainly dependent on thecutting efficiency of the machine, job organization, theexperience of the contractor, skill of the operator, unex-pected geological conditions, machine available timeand machine utilization time (Bilgin et al., 1999b).

9. Conclusions and suggestions

In comparison to limestone zones, due to their brittlenature, shales in the Tuzla tunnel were more affected bytectonism. RMR rock mass classification and supportsystems for the fault zones were insufficient for describ-ing deformation, failure mechanisms and other phenom-enon encountered during the tunnel excavation. Inaddition, dyke rocks and karstic systems collapsed byfaulting caused some problems during the tunnel exca-vation. Another potential effect of faults on a tunnel isseismicity. It was observed that the Tuzla tunnel wasnot damaged during the 17th August Izmit and the 12thNovember Duzce earthquakes. Distances of earthquakeepicenters to the tunnel, the value of ground acceleration,the construction of outer and inner concrete linings, thesmallness of tunnel diameter and the low primary stressdistribution must have played an important role for thetunnel to have no damage.The biggest impact of faults on the tunnel is their

inadequate exploration in exploratory drillings. On thebasis of drilling data, fault zones showed very poor tofair rock qualities and also excavation and support withthe TBM method were thought to be economic. How-ever, the tunnel excavation had to be performed in faultzones of very poor to poor rock quality that comprised70% of the total tunnel length. Fault zones causedsubsidence, jamming of the TBM cutter and shield,deviations from the tunnel axis, low progress rates andsome other problems in excavation and support works.In areas of fault zones, selection of the conventional

method rather than the TBM method made it easier to


apply additional support measures. In tunnel investiga-tions, exploration of fault zones and dyke rocks thatcannot be determined with drilling requires detailedworks and technical equipment capable of high corerecovery efficiency. In other cases, similar to the Tuzlatunnel, faults that cannot be predicted may have anegative effect on time and project and constructioncosts. New rock classification parameters are also need-ed to determine deformation and behavior in fault zoneenvironments. In this respect, development of new appli-cable classifications will be beneficial.

Acknowledgments

The Author wishes to thank the staff of the STFACompany for access to data on the Tuzla tunnel.

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Tunneling in fault zones, Tuzla tunnel, TurkeyIntroductionGeneral geology of the tunnelIn situ testsLaboratory testsGeological strength index classificationRock mass strengthRock mass valuesEvaluations of the fault zonesEvaluations of drilling data in the fault zonesProblems arising from dyke rocks in the fault zonesRock mass values in fault zonesDisadvantages of rock mass applications in the fault zonesEffect of groundwater in fault zonesEffect of fault zones on karstic environmentsSeismicity of the fault zoneSupport and excavation with conventional system in the fault zonesSupport and excavation with TBM in the fault zones

Conclusions and suggestionsAcknowledgementsReferences

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Tunneling in fault zones, Tuzla tunnel, Turkey

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