Underground Space Use: Analysis of the Past and Lessons for the Future – Erdem & Solak (eds)© 2005 Taylor & Francis Group, London, ISBN 04 1537 452 9

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1 INTRODUCTION

The Bosphorus railway tube crossing project extendsfrom Sögütlüçesme to Kazlicesme with a total lengthof 13,558 km (Figure 1). The project includes;

• 1600 m immersed tube, (at base elevation of �55to �60 m, deepest immersed tube in the world),

• 10133 m bored tunnel (double tube),• 1910 m cut & cover tunnel (stations included),• 1300 m retaining fill and cut and at grade structures

Initial geological and geotechnical investigationswere carried out in 1985–1987 during a preliminarydesign stage. Detailed site investigations were con-ducted in 2002 and 2003 during the final design stageand construction tender period.

2 INVESTIGATION PERFORMED

2.1 Investigation in 1985–1987

The 1985 to 1987 investigations were performedbetween Yenikapi and Sögütlüçesme stations andincluded core drilling in rock and soil with systematicStandard Penetration Testing (SPT) and sampling. Atotal length of 772 m boreholes at 20 locations onwater and 1394 m at 37 locations on land were carriedout. Geophysical and bathymetric surveys were con-ducted across the Bosphorus. Physical properties ofthe rock and soil were determined by laboratory tests.

The off-shore investigation was carried out on abarge using conventional drilling equipment. In thismethod, the casing sunk into soft soil from mud lineto some depth by its own weight and many of the SPTN values were counted as 0. This situation causedmisleading measurements of water depth at the bore-hole locations and unreliable estimate of the shearstrength of the soil.

Marmaray project: geological and geotechnical investigations

Orhan SimsekEngineering Geologist (Bosphorus Crossing); ( Sial Yerbilimleri, Turkey)

Satoshi MitaniDesign Supervisor (Bosphorus Crossing); (Pacific Consultants International, Japan)

Osman AltunGeophysichts (Bölge Müdürlüg�ü, Turkey)

ABSTRACT: Preliminary site investigations for the Bosphorus rail tube tunnel project were carried out in1985–1987. Additional site investigations for offshore and on-shore sections using modern techniques wereconducted in 2002 and 2003. The objective of the off-shore investigations was to define the soil types of themarine deposits, soil/rock boundaries and geotechnical parameters of the soil layers to enable contractors toevaluate potential risk for liquefaction under seismic conditions, slope stability of the dredged trench, heave andsettlement of clay layers at the bottom of the trench along the immersed tunnel alignment and the dynamic prop-erties of soil and rock to be used in seismic hazard assessment. The objective of the investigations along thebored tunnels and cut & cover sections was to determine the soft ground and rock boundaries, geotechnical andstructural properties of rock and soil, groundwater conditions and permeability.

Figure 1. Plan view of gunnel alignment.

2.2 Investigation in 2002–2003

An additional investigation program was carried outfor the section from Yedikule to Sögütlüçesme in2002 and 2003. This program included:

• A total length of 1070 m core drilling in 26 location,• Undisturbed and SPT sampling in soil layers,• Geophysical survey (up/down hole and cross hole)

at deep stations,• Laboratory testing to define the physical and

geomechanical properties of the rock and soil.

Off shore

• A total number of seven boreholes with total lengthof 350 m and maximum 85 m depth from seabedlevel with continuous Cone Penetration Testing(CPT) and undisturbed sampling every 3 m in soiland continuous coring in rock,

• Continuous CPT tests down to maximum depth of40 m below seabed at 3 locations,

• P-S logging in 2 holes, from seabed level to 10 minto bedrock,

• Environmental sampling and testing from seabeddown to approximately 9 m,

• Geotechnical laboratory testing.

Off-shore drilling was performed by Fugro Engi-neers, from the Netherlands, using the marine vesselBavenit, which maintains its location on water by adynamic positioning system.

CPT testing was conducted using the Wison typeequipment (Figure 2), which consist of a down holejacking unit with a 3 m stroke and a thrust capacity of90 kN. The Wison type CPT equipment is used in con-junction with a flush rotary drilling system and openbit. After the borehole has reached the required depth,the Wison unit is lowered by its electro-hydraulicumbilical to the bit, where it seats and latches underits own weight. The cone penetrometer is then hydrauli-cally pushed into the soil at a constant rate of 20 mm/s.The measurements of cone tip resistance, sleeve fric-tion and pore pressure are displayed graphically in thecontrol cabin and electronically recorded.

The geophysical and bathymetric surveys extendedto a width of 500 m on both sides of the immersedtube tunnel alignment. The geophysical survey includedsingle channel boomer and sparker methods. The singlechannel boomer was carried out with parallel (parallelto the route corridor) profiles spacing of 100 m andcross profiles (at right angle to the route corridor) at aspacing of 25 m. The sparker method was measuredalong 3 parallel profiles (along the proposed alignmentcenterline and one profile along each side of the align-ment) and cross profiles at spacing of 100 m.

The first 50 m of depth below the channel have avertical resolution of less then 25 cm for boomeroperation. The sparker system was used down to

approximately 100 m from seabed, with a vertical resolution of less than 2 m.

3 RESULTS OF INVESTIGATION

3.1 Bored tunnel

Based on the findings of the site investigation describedabove, the predicted ground conditions along the boredtunnel alignment can be summarized as indicated inTable 1 and in geological profiles (Figures 3 and 4):

As seen in Table 1, three major formations will beencountered along the bored tunnel alignment:

Bakirköy Formation will likely be encountered fromkm 0 � 960 to km 2 � 400 and consist of silty sandyclay with calcareous lenses. The clayey layers are highlyover-consolidated and are in stiff to very stiff consis-tency. The calcareous lenses bear groundwater. SPT Nblows are usually higher than 30 at tunnel level and gen-erally increase with the depth (Figure 5). According toUnified Soil Classification System (Casagrande1948), the cohesive layer of the Bakirköy Formationis classified as CH and the cohesionless layers areclassified as SC, SP-SC and SW-SC (see Figure 6).

Süleymaniye Formation will likely be encounteredalong the bored tunnel section from km 2 � 400 to4 � 560 consisting of silty clay with sandy lenses. Theclayey layers are highly over-consolidated and are instiff to very stiff consistency. The sandy lenses bears

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Figure 2. Wison type CPT equipment.

usually confined perched groundwater. According tothe Unified Soil Classification System, the cohesivelayer of the Süleymaniye Formation is usually classi-fied as CH and MH-OH (Figure 7). The sandy lensesare classified as SC, SP-SC and SW-SC. SPT N blowsversus depth relation is shown in Figure 8.

The Trakya Formation is made up of yellowishbrown to dark gray colored sandstone, siltstone andmudstone (shale) sequences. The rock mass is usuallymedium weathered to fresh and exhibits closely tomoderate closely spaced discontinuities. The strengthproperties of the intact rock are in the range of weakto very strong. Dyke intrusions will likely be encoun-tered frequently during tunneling.

From a geotechnical point of view the TrakyaFormation can be divided into three groups;

Faulted/sheared rock mass: This zone will usuallybe encountered at fault zone areas with thickness offrom several decimeters to few meters, at shearedmudstone (shale) layers and at dyke contact. Intactrock Uniaxial Compressive Strength values (UCS)vary from 2 MPa to 20 MPa.

Average rock mass: This rock mass is composed ofsandstone, siltstone and mudstone (shale) sequences.The rock mass is medium strong to very strong andshows 70 MPa UCS in average. Abrasiveness of therock mass is expected in the range of from not abra-sive-to-abrasive.

Competent rock: This rock mass represents freshand very strong sandstone (intact UCS is higher than180 MPa) and fresh diabase type dyke intrusion.

3.1 Immersed tube section

Based on the investigation results, the geological con-ditions and lithological stratification are interpretedas shown in the geological profile (Figure 10). Takinginto consideration the grain size distribution, densityand consistency of the soils along the immersed tubetunnel alignment, the marine deposits can be distin-guished into eight geotechnical units (excludingrock), as summarized in Table 2.

Geotechnical unit A refers to contaminated soil.These layers will be dredged and disposed in a con-fined disposal facilities.

Geotechnical unit B refers to gray colored, fine tocoarse – grained sand with silt and little clay content.This unit is encountered at the upper level of the tubetunnel profile and is not present below the foundationlevel of the tube between km 7 � 390 and 7 � 900.The cone resistance in this unit is generally ratherlow, in the range of 0.5 MPa to 4 Mpa, which corre-sponds to very loose to loose soil. Locally, the coneresistance is as high as 12 MPa. This unit will beencountered below the invert of the tube alignmentbetween km 7 � 900 and km 8 � 680. The CPT coneresistance is relatively high and increases with depth.It ranges from 4 MPa to 12 MPa in first 8 m to 12 m.Below this depth, unit B has higher cone resistance(more than 12 MPa) due to interlayering with unit E.

Geotechnical Unit C represents the gray coloredsandy clay/clayey sand layer, which is situated abovethe immersed tube foundation level. This unit islocated from km 7 � 390 to 7 � 900. CPT tests indi-cate rather low cone resistance (0.2 MPa to 2 MPa),which corresponds to very soft to soft/very loose toloose consistency and density.

Geotechnical unit D consists of gray colored siltyclay (Golden Horn Clay) with medium plasticity andvery soft-to-soft consistency. This unit is presentbelow the foundation of the immersed tube tunnelbetween km 7 � 390 and km 7 � 900 and therefore isconsidered one of the main geotechnical units influ-encing the construction works. The cone resistance ofthis clay is rather low, averaging about 0.5 MPa, whichcorresponds to very soft consistency (see Figure 9).

Geotechnical Unit E is composed of gray sandyclay with low to medium plasticity, and firm to stiffconsistency. H2S gasses were measured from the

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Table 1. Summary of ground conditions along Bored tunnel.

Chainage (km) Structure Formation

Till km 0 � 960 At Grade Artificial Fill0 � 960–1 � 500 Cut & Cover Artificial Fill

Bakirköy Formation

1 � 500–2 � 420 Bored Tunnel Bakirköy Formation

2 � 420–3 � 310 Bored Tunnel Süleymaniye Formation

3 � 310–4 � 090 Artificial FillMarine Deposits

Cut & Cover Süleymaniye (Yenikapi Station) Formation

Trakya Formation4 � 090–4 � 140 Bored Tunnel Süleymaniye

Formation4 � 140–4 � 420 Bored Tunnel Trakya Formation4 � 420–4 � 560 Bored Tunnel Süleymaniye

FormationTrakya Formation

4 � 560–6 � 240 Bored Tunnel Trakya Formation6 � 240–6 � 420 Sirkeci Station Trakya Formation6 � 420–7 � 320 Bored Tunnel Trakya Formation8 � 890–9 � 550 Bored Tunnel Trakya Formation9 � 550–9 � 880 Üsküdar Station Artificial Fill

Marine DepositsTrakya Formation

9 � 880–12 � 795 Bored Tunnel Trakya Formation12 � 795–12 � 920 Bored Tunnel Alluvium

Trakya Formation12 � 920–13 � 415 Bored Tunnel Trakya Formation13 � 415–13 � 860 Cut & Cover, At Artificial Fill

Grade Structures AlluviumTrakya Formation

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sample obtained from this unit. This unit is encoun-tered in the central and eastern part of the tube tunnelalignment. Since it is found below elevation �55.0 m,it is assumed that this unit will not appear within thelimits of proposed tunnel trench. The cone resistanceof this unit generally ranges from 1.0 to 2 MPa, whichcorresponds to firm to stiff consistency.

Geotechnical Unit F contains light gray-to-graysandy shell deposits, which is present between km8 � 180 and 8 � 780. This unit appears from seabedlevel to �43.0 m.

Geotechnical Unit G is made up of gray silty sandygravel with shell fragments. This coarse grained soilis present at the eastern side of the tube tunnel align-ment between approximately km 8 � 680 and 8 � 790.

Geotechnical Unit H contains coarser gain sizemarine deposits composed of sand, gravel, cobble andboulders. Maximum boulder size is expected to beapproximately 1 m diameter.

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0

5

10

15

20

25

30

0 10 20 40

Blow Number

DE

PT

H m

30 50

Figure 5. SPT N values versus depth.

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Liquid limit (Wl)

Pla

stic

ity

Ind

ex (

Ip) Line Ip = 0,73 (Wl-20)

CL

CH

CL

ML or OLCL - ML

MH or OH

ML

cohesionless soils7 4

Figure 6. Plasticity chart, Bakirköy formation.

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Liquid Limit (Wl)

Pla

stic

ity

Ind

ex (

Ip)

Line Ip = 0,73 (Wl-2)

CL

CH

CL

ML or OLCL - ML

MH or OH

ML

cohesionless soils7

4

Figure 7. Plasticity chart, Süleymaniye formation.

0

5

10

15

20

25

30

35

40

45

50

0 10 20 30 40 50

Blow Number

DE

PT

H m

Figure 8. SPT N values versus depth.

-40

-35

-30

-25

-20

-15

-10

-5

0

0 20 40 60 80

Shear Strength-kPa

Dep

th (

m)

Torn vane

Pocket Penetrometer

Triaxial UU

Figure 9. Depth un-drained shear strength of unit D.

P-waves, S-waves and shear modulus of the vari-ous geotechnical units were measured in two bore-holes by Seismic CPT tools. Shear wave velocity andsmall-strain shear modulus profiles measured in oneof these borings is presented in Figure 11.

4 CONCLUDING REMARKS

Geological and geotechnical investigations for theproposed Bosphorus rail tube tunnel crossing werecarried out during a preliminary design phase in1985–1987 and a final design and construction tenderphase in 2002–2003.

The off-shore preliminary geotechnical investiga-tion in 1985–1987 was performed using conventionaldrilling methods with SPT tests and undisturbed sam-ples, whereas modern investigation techniques wereused during final design and construction tender stageby means of a vessel which is capable of maintainingits location by a dynamic positioning system. In thissystem, continuous CPT testing was performed andundisturbed soil samples were obtained at 3 m inter-vals. The data obtained from the recent investigationwere found more reliable for defining the soil stratifi-cation, index properties and strength properties of thevarious soil layers.

REFERENCES

Büchi E., Mathier J. –F., Wyss Ch., 1995, Rock abrasivity –a significant cost factor for mechanical tunnelling inloose and hard rock, Tunnel 5/95, Cologne: 38–44.

Casagrande A. (1948), Classification and identification ofsoil, Transaction ASCE, vol. 113, pp. 901–991.

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Figure 10. Geological profile, immersed tube section.

Table 2. Summary of ground conditions.

Units Lithological descriptions

A Artificial fill, contaminated soilB Light gray to dark gray sandC Gray Sandy Clay/clayey sandD Gray Silty clay, very soft with sandy lensesE Gray sandy clayF Light gray to gray sandy shell depositsG Gray Silty sandy gravelH Gray sandy gravel

Figure 11. Shear wave velocity (m/s) and small-strainshear modulus at borehole BH-3.