ORIGINAL ARTICLE

Surface settlement predictions for Istanbul Metro tunnelsexcavated by EPB-TBM

S. G. Ercelebi • H. Copur • I. Ocak

Received: 13 July 2009 / Accepted: 15 March 2010

� Springer-Verlag 2010

Abstract In this study, short-term surface settlements are

predicted for twin tunnels, which are to be excavated in the

chainage of 0 ? 850 to 0 ? 900 m between the Esenler

and Kirazlı stations of the Istanbul Metro line, which is

4 km in length. The total length of the excavation line is

21.2 km between Esenler and Basaksehir. Tunnels are

excavated by employing two earth pressure balance (EPB)

tunnel boring machines (TBMs) that have twin tubes of

6.5 m diameter and with 14 m distance from center to

center. The TBM in the right tube follows about 100 m

behind the other tube. Segmental lining of 1.4 m length is

currently employed as the final support. Settlement pre-

dictions are performed with finite element method by using

Plaxis finite element program. Excavation, ground support

and face support steps in FEM analyses are simulated as

applied in the field. Predictions are performed for a typical

geological zone, which is considered as critical in terms of

surface settlement. Geology in the study area is composed

of fill, very stiff clay, dense sand, very dense sand and hard

clay, respectively, starting from the surface. In addition to

finite element modeling, the surface settlements are also

predicted by using semi-theoretical (semi-empirical) and

analytical methods. The results indicate that the FE model

predicts well the short-term surface settlements for a given

volume loss value. The results of semi-theoretical and

analytical methods are found to be in good agreement with

the FE model. The results of predictions are compared and

verified by field measurements. It is suggested that grouting

of the excavation void should be performed as fast as

possible after excavation of a section as a precaution

against surface settlements during excavation. Face pres-

sure of the TBMs should be closely monitored and adjusted

for different zones.

Keywords Surface settlement prediction �Finite element method � Analytical method �Semi-theoretical method � EPB-TBM tunneling �Istanbul Metro

Introduction

Increasing demand on infrastructures increases attention to

shallow soft ground tunneling methods in urbanized areas.

Many surface and sub-surface structures make under-

ground construction works very delicate due to the influ-

ence of ground deformation, which should be definitely

limited/controlled to acceptable levels. Independent of the

excavation method, the short- and long-term surface and

sub-surface ground deformations should be predicted and

remedial precautions against any damage to existing

structures planned prior to construction. Tunneling cost

substantially increases due to damages to structures

resulting from surface settlements, which are above toler-

able limits (Bilgin et al. 2009).

Basic parameters affecting the ground deformations are

ground conditions, technical/environmental parameters and

tunneling or construction methods (O’Reilly and New

1982; Arioglu 1992; Karakus and Fowell 2003; Tan and

Ranjit 2003; Minguez et al. 2005; Ellis 2005; Suwansawat

and Einstein 2006). A thorough study of the ground by site

investigations should be performed to find out the physical

S. G. Ercelebi (&) � H. Copur

Mining Engineering Department, Istanbul Technical University,

Maslak, 34469 Istanbul, Turkey

e-mail: ercelebi@itu.edu.tr

I. Ocak

Rail Transportation Department (IETT), Istanbul Metropolitan

Municipality, Istanbul, Turkey

123

Environ Earth Sci

DOI 10.1007/s12665-010-0530-6

and mechanical properties of the ground and existence of

underground water, as well as deformation characteristics,

especially the stiffness. Technical parameters include tun-

nel depth and geometry, tunnel diameter–line–grade, single

or double track lines and neighboring structures. The

construction method, which should lead to a safe and

economic project, is selected based on site characteristics

and technical project constraints and should be planned so

that the ground movements are limited to an acceptable

level. Excavation method, face support pressure, advance

(excavation) rate, stiffness of support system, excavation

sequence and ground treatment/improvement have dra-

matic effects on the ground deformations occurring due to

tunneling operations.

The primary reason for ground movements above the

tunnel, also known as surface settlements, is convergence

of the ground into the tunnel after excavation, which

changes the in situ stress state of the ground and results in

stress relief. Convergence of the ground is also known as

ground loss or volume loss. The volume of the settlement

on the surface is usually assumed to be equal to the ground

(volume) loss inside the tunnel (O’Reilly and New 1982).

Ground loss can be classified as radial loss around the

tunnel periphery and axial (face) loss at the excavation face

(Attewell et al. 1986; Schmidt 1974). The exact ratio of

radial and axial volume losses is not fully demonstrated or

generalized in any study. However, it is possible to

diminish or minimize the face loss in full-face mechanized

excavations by applying a face pressure as a slurry of

bentonite–water mixture or foam-processed muck. The

ground loss is usually more in granular soils than in

cohesive soils for similar construction conditions. The

width of the settlement trough on both sides of the tunnel

axis is wider in the case of cohesive soils, which means

lower maximum settlement for the same amount of ground

loss.

Time dependency of ground behavior and existence of

underground water distinguish short- and long-term set-

tlements (Attewell et al. 1986). Short-term settlements

occur during or after a few days (mostly a few weeks) of

excavation, assuming that undrained soil conditions are

dominant. Long-term settlements are mostly due to creep,

stress redistribution and consolidation of soil after drainage

of the underground water and elimination of pore water

pressure inside the soil, and it may take a few months to a

few years to reach a stabilized level. In dry soil conditions,

the long-term settlements may be considered as very

limited.

There are mainly three settlement prediction approaches

for mechanized tunnel excavations: (1) numerical analysis

such as finite element method, (2) analytical method and

(3) semi-theoretical (semi-empirical) method. Among

them, the numerical approaches are the most reliable ones.

However, the results of all methods should be used care-

fully by an experienced field engineer in designing the

stage of an excavation project.

In this study, all three prediction methods are employed

for a critical zone to predict the short-term maximum

surface settlements above the twin tunnels of the chainage

between 0 ? 850 and 0 ? 900 m between Esenler and

Kirazlı stations of Istanbul Metro line, which is 4 km in

length. Plaxis finite element modeling program is used for

numerical modeling; the method suggested by Loganathan

and Poulos (1998) is used for the analytical solution. A few

different semi-theoretical models are also used for predic-

tions. The results are compared and validated by field

measurements.

Description of the project, site and construction method

The first construction phase of Istanbul Metro line was

started in 1992 and opened to public in 2000. This line is

being extended gradually, as well as new lines are being

constructed in other locations. One of these metro lines is

the twin line between Esenler and Basaksehir, which is

21.2 km. The excavation of this section has been started

in May 2006. Currently, around 1,400 m of excavation

has already been completed. The region is highly popu-

lated including several story buildings, industrial zones

and heavy traffic. Alignment and stations of the metro

line between Esenler and Basaksehir is presented in

Fig. 1.

Totally four earth pressure balance (EPB) tunnel bor-

ing machines (TBM) are used for excavation of the

tunnels. The metro lines in the study area are excavated

by a Herrenknecht EPB-TBM in the right tube and a

Lovat EPB-TBM in the left tube. Right tube excavation

follows around 100 m behind the left tube. Some of the

technical features of the machines are summarized in

Table 1.

Excavated material is removed by auger (screw con-

veyor) through the machine to a belt conveyor and than

loaded to rail cars for transporting to the portal. Since the

excavated ground bears water and includes stability prob-

lems, the excavation chamber is pressurized by 300 kPa

and conditioned by applying water, foam, bentonite and

polymers through the injection ports. Chamber pressure is

continuously monitored by pressure sensors inside the

chamber and auger. Installation of a segment ring with 1.4-

m length (inner diameter of 5.7 m and outer diameter of

6.3 m) and 30-cm thickness is realized by a wing-type

vacuum erector. The ring is configured as five segments

plus a key segment. After installation of the ring, the

excavation restarts and the void between the segment outer

perimeter and excavated tunnel perimeter is grouted by

Environ Earth Sci

123

300 kPa of pressure through the grout cannels in the

trailing shield. This method of construction has been pro-

ven to minimize the surface settlements.

The study area includes the twin tunnels of the chai-

nage between 0 ? 850 and 0 ? 900 m, between Esenler

and Kirazlı stations. Gungoren Formation of the Miosen

age is found in the study area. Laboratory and in situ tests

are applied to define the geotechnical features of the

formations that the tunnels pass through. The name,

thickness and some of the geotechnical properties of the

layers are summarized in Table 2 (Ayson 2005). Fill layer

of 2.5-m thick consists of sand, clay, gravel and some

pieces of masonry. The very stiff clay layer of 4 m is

grayish green in color, consisting of gravel and sand. The

dense sand layer of 5 m is brown at the upper levels and

greenish yellow at the lower levels, consisting of clay, silt

and mica. Dense sand of 3 m is greenish yellow and

consists of mica. The base layer of the tunnel is hard clay,

which is dark green, consisting of shell. The underground

water table starts at 4.5 m below the surface. The tunnel

axis is 14.5 m below the surface, close to the contact

between very dense sand and hard clay. This depth is

Marmara Sea

Aksaray

Otogar

Ba ak ehir

0 km 5 km

European Side

Anatolia Side

Bosphorus

Bakırkoy IDO

Halkalı

Olimpiyat köyü

Güney sanayi

Atatürk Airport

Golden Horn

Kirazlı 1

0+000 0+500 1+000 1+500 2+000 2+500 3+000 3+500 4+000 4+500 5+000 Viad. At Grade R.W Bored Tunnel Bored Tunnel Bored Tunnel Bored Tunnel

10

20

30

40

50

60

70

80

Cut& Cover

Cut&Cover

Cut&Cover

Cut&Cover

Structure Type

Kilometer

Fill Clay

Sand Trakya formation

Metro line

0 m 250 m

Fig. 1 Main route and geological section of Esenler and Basaksehir Metro Line (Ocak 2009)

Table 1 Some of the technical features of the EPB-TBMs

Herrenknecht Lovat

Excavation diameter 6.500 m 6.564 m

Shield outside diameter 6.45 m 6.52 m

TBM length 7.68 m 9.30 m

Backup length 80 m 65 m

Total weight 578 t 534 t

Maximum cutter head RPM 0–2.5 0–6.0

Total installed power 963 kW 1,622 kW

Cutter head type Mixed ground Mixed ground

Cutter head power 630 kW 900 kW

Maximum torque 435 t m 445 t m

Maximum thrust 32.000 kN 54.000 kN

Environ Earth Sci

123

quite uniform in the chainage between 0 ? 850 and

0 ? 900 m.

Surface settlement prediction with finite element

modeling

Plaxis finite element code for soil and rock analysis is used

to predict the surface settlement. First, the right tube is

constructed, and then the left tube 100 m behind the right

tube is excavated. This is based on the assumption that

ground deformations caused by the excavation of the right

tube are stabilized before the excavation of the left tube.

The finite element mesh is shown in Fig. 2 using 15 stress

point triangular elements. The FEM model consists of

1,838 elements and 15,121 nodes. In FE modeling, the

Mohr–Coulomb failure criterion is applied.

Staged construction is used in the FE model. Excavation

of the soil and the construction of the tunnel lining are

carried out in different phases. In the first phase, the soil in

front of TBM is excavated, and a support pressure of

300 kPa is applied at the tunnel face to prevent failure at

the face. In the first phase, TBM is modeled as shell ele-

ments. In the second phase, the tunnel lining is constructed

using prefabricated concrete ring segments, which are

bolted together within the tunnel boring machine. During

the erection of the lining, TBM remains stationary. Once a

lining ring has been bolted, excavation is resumed until

sufficient soil excavation is carried out for the next lining.

The tunnel lining is modeled using volume elements. In the

second phase, the lining is activated and TBM shell ele-

ments are deactivated.

When applying finite element models, volume loss

values are usually assumed prior to excavation. In this

study, the FEM model is run with the assumption of 0.5,

0.75, 1 and 1.5% volume loss caused by the convergence of

the ground into the tunnel after excavation. Figures 3 and 4

show total and vertical deformations after both tubes are

constructed. The vertical ground settlement profile after the

right tube construction is given in Fig. 5, which is in the

shape of a Gaussian curve, and that after construction of

both tubes is given in Fig. 6. Figure 7 shows the total

deformation vectors.

The maximum ground deformations under different

volume loss assumptions are summarized in Table 3.

Surface settlement prediction with semi-theoretical

and analytical methods

Semi-theoretical predictions for short-term maximum set-

tlement are performed using the Gaussian curve approach,

which is a classical and conventional method. The settle-

ment parameters used in semi-theoretical estimations and

notations are presented in Fig. 8.

The theoretical settlement (Gaussian) curve is presented

as in Eq. 1 (O’Reilly and New 1982):

S ¼ Smaxe�x2

2i2

� �ð1Þ

where, S is the theoretical settlement (Gauss error function,

normal probability curve), Smax is the maximum short-term

(initial, undrained) settlement at the tunnel centerline (m),

x is the transverse horizontal distance from the tunnel

center line (m), and i is the point of inflexion (m). To

determine the shape of a settlement curve, it is necessary to

predict i and Smax values.

There are several suggested methods for prediction of

the point of inflexion (i). Estimation of i value in this study

Table 2 Geotechnical properties of the study area (Ayson 2005)

Formation Thickness (m) N30 SU (kPa) / (�) Ea (kPa) cn (kN/m3) cdry (kN/m3) PI (%) Permeability (cm/s)

Fill 2.5 10 13 20 8,000 19.8 13.8 – 1.0

Very stiff clay 4.0 20 85 9 51,000 18.2 12.7 33 1.0 9 10-4

Dense sand 5.0 35 40 35 24,000 19.0 13.5 – 0.5

Very dense sand 3.0 64 50 35 30,000 19.5 15.0 – 0.25

Hard clay Base 45 150 12 90,000 18.6 14.0 45 1.0 9 10-4

N30 Standard penetration number, SU undrained shear strength, / internal friction angle, E elasticity modulus, cn natural unit weight, cdry dry unit

weight, PI plasticity indexa Estimated as E = 600 SU

Fig. 2 Finite element model

Environ Earth Sci

123

Fig. 3 Total deformations after

left tube construction

Fig. 4 Vertical deformations

after left tube construction

0

-5

-10

-15 Surf

ace

Settl

emen

t (m

m)

0 10 20 30 40 50

Distance from the Centerline of Two Tubes (m)

Fig. 5 Surface settlements after construction of the right tube

0 10 20 30 40 50

Distance from the Centerline of Two Tubes (m)

0

-5

-10

-15

Surf

ace

Settl

emen

t (m

m)

Fig. 6 Surface settlements after both tubes are constructed

Environ Earth Sci

123

is based on averages of some empirical approaches given in

Eqs. 2–6:

i ¼ i1 þ i2 þ i3 þ i4

4ð2Þ

i1 ¼ 0:5Z0 ð3Þi2 ¼ 0:43Z0 þ 1:1 ð4Þ

i3 ¼ RZ0

2R

� �0:8

ð5Þ

i4 ¼ 0:9RZ0

2R

� �0:88

ð6Þ

where, Z0 is the tunnel axis depth (m), 14.5 m in this study,

and R is the radius of tunnel, 3.25 m in this study. Equa-

tion 3 was suggested by Glossop (O’Reilly and New 1982)

for mostly cohesive grounds; Eq. 4 was suggested by

O’Reilly and New (1982) for excavation of cohesive

grounds by shielded machines; Eq. 5 was suggested by

Schmidt (1969) for excavation of clays by shielded

machines; Eq. 6 was suggested by Arioglu (1992) for

excavation of all types of soils by shielded machines. As a

result, the average i value is estimated to be 6.6 m in this

study.

There are several suggested empirical methods for the

prediction of the maximum surface settlement (Smax).

Schmidt suggested a model for the estimation of Smax value

for a single tunnel in 1969 as given in Eq. 7 (through

Arioglu 1992):

Smax ¼ 0:0125KR2

i

� �ð7Þ

where, K is the volume loss (%). Arioglu (1992), based on

field data, found a good relationship between K and N

(stability ratio) for face-pressurized TBM cases as in Eq. 8:

K ¼ 0:87e0:26N ¼ 0:87e0:26

cnZ0þrSþrTCU

� �

ð8Þ

where cn is the natural unit weight of the soil (kN/m3), the

weighted averages for all the layers, which is 19 kN/m3 in

this study; rS is the total surcharge pressure (kPa), assumed

to be 20 kPa in this study; rT is TBM face pressure (kPa),

which is 300 kPa in this study; and CU is the undrained

cohesion of the soil (kPa), the weighted averages for all the

layers, which is 50 kPa in this study assuming that CU is

equal to SU (undrained shear strength of the soil). All

averages are estimated up to very dense sand, excluding

hard clay, since the tunnel axis passes around the contact

between very dense sand and hard clay. The model yields

17.1 mm of initial maximum surface settlement.

Herzog suggested a model for the estimation of Smax

value in 1985 as given in Eq. 9 for a single tunnel and

Eq. 10 for twin tunnels (through Arioglu 1992):

Smax ¼ 0:785 cnZ0 þ rSð Þ D2

iE

� �ð9Þ

Smax ¼ 4:71 cnZ0 þ rSð Þ D2

3iþ að ÞE

� �ð10Þ

where, E is the elasticity modulus of formation (kPa), the

weighted averages for all the layers, which is 30,000 kPa in

this study, and a is the distance between the tunnel axes,

which is 14 m in this study. The model yields 49.9 and

58.7 mm of initial maximum surface settlements for the

right and the left tube tunnel, which is 100 mm behind the

right tube, respectively.

There are several analytical models for the prediction of

short-term maximum surface settlements for shielded tun-

neling operations (Lee et al. 1992; Loganathan and Poulos

1998; Chi et al. 2001; Chou and Bobet 2002; Park 2004).

The method suggested by Loganathan and Poulos (1998) is

used in this study. In this method, a theoretical gap

0

-5

-10

-15 Surf

ace

Settl

emen

t (m

m) 0 10 20 30 40 50

Distance from the Centerline of Two Tubes (m)

Fig. 7 Total deformation vectors on the surface

Table 3 Maximum surface settlements obtained by FEM

Volume loss (%) Right tube (mm) Left tube (mm)

0.5 12.35 20.22

0.75 14.19 22.43

1.0 15.89 24.34

1.5 18.62 27.49

Maximum Surface Settlements

0

5

10

15

20

25

30

0.5 0.75 1 1.5

Volume Loss (%)

Set

tlem

ent (

mm

)

Right TubeLeft Tube

Fig. 8 Maximum surface settlements for left and right tubes

Environ Earth Sci

123

parameter (g) is defined based on physical gap in the void,

face losses and workmanship value, and then the gap

parameter is incorporated to a closed form solution to

predict elastoplastic ground deformations. The undrained

gap parameter (g) is estimated by Eq. 12:

g ¼ Gp þ U�3D þ w ð12Þ

where Gp is the physical gap (Gp = 2D ? d) representing

the geometric clearance between the outer skin of the

shield and the liner, D is the thickness of the tail shield, d is

the clearance required for erection of the liner, U�3D is the

equivalent 3D elastoplastic deformation at the tunnel face,

and w is a value that takes into account the quality of

workmanship.

Maximum short-term surface settlement is predicted by

theoretical Eq. 13 (Loganathan and Poulos 1998):

S ¼ 4 1� tð ÞR2 Z0

Z20 þ x2

� �4gRþ g2

R2

� �exp

�1:38x2

Z0 þ Rð Þ2

" #

ð13Þ

where, t is undrained Poisson’s ratio, assumed to be of

maximum 0.5; g is the gap parameter (m), which is esti-

mated to be 0.0128 m in this study; and x is transverse

distance from the tunnel centerline (m) and it is assumed to

be 0 m for the maximum surface settlement. The model

yields 23.0 mm of undrained maximum surface settlement.

Other parameters of settlement such as maximum slope,

maximum curvature and so on are not mentioned in this

study.

Verification of predictions by field measurements

and discussion

The results of measurements performed on the surface

monitoring points, by Istanbul Metropolitan Municipality,

are presented in Table 4 for the left and right tubes. As

seen, the average maximum surface settlements are

around 9.6 mm for the right tube and 14.4 mm for the left

tube, which excavates 100 m behind the right tube. The

maximum surface settlements measured around 15.2 mm

for the right tube and 26.3 mm for the left tube. Higher

settlements are expected in the left tube since the previous

TBM excavation activities on the right tube overlaps the

previous deformation. The effect of the left tube exca-

vation on deformations of the right tube is presented in

Fig. 9. As seen, after Lovat TBM in the right tube

excavates nearby the surface monitoring point 25, maxi-

mum surface settlement reaches at around 9 mm; how-

ever, while Herrenknecht TBM in the left tube passes the

same point, maximum surface settlement reaches at

around 29 mm (Fig. 10).

If the construction method applied to the site is con-

sidered, long-term (consolidation) settlements are expected

to be low, since the tail void is grouted immediately after

excavation. The results of predictions mentioned above and

observed maximum surface settlements are summarized in

Table 5.

The methods suggested by Loganathan and Poulos

(1998) and Schmidt (1969) connected with Arioglu’s

suggestion (1992) can predict the maximum short-term

surface settlements only for a single tunnel. Plaxis finite

element and Herzog (1985) models can predict deforma-

tions for twin tubes.

Herzog’s model (1985) yields higher maximum surface

settlements than the observed ones. The reason for that is

that the database of the model includes both shielded

Table 4 Short-term maximum surface settlement values obtained

from surface monitoring point (SMP) measurements between chai-

nage 0 ? 850 and 0 ? 900 m

Left tube Right tube

SMP no. Smax (m) SMP no. Smax (m)

14 -0.0093 33 -0.0142

15 -0.0045 34 -0.0101

16 0.0102 35 -0.0084

17 -0.0263 36 -0.0113

18 -0.0235 37 -0.0070

19 -0.0163 38 -0.0065

20 -0.0183 39 -0.0059

21 -0.0200 40 -0.0074

22 -0.0177 41 -0.0152

23 -0.0248

24 -0.0220

25 -0.0089

26 -0.0075

31 -0.0117

32 -0.0152

Average -0.0144 Average -0.0096

Fig. 9 Settlement parameters and notation

Environ Earth Sci

123

tunnels and NATM (New Austrian Tunneling Method)

tunnels, of which surface settlements are usually higher

compared to shielded tunnels. Schmidt (1969), along with

Arioglu’s suggestion (1992), yields predictions close to

observed values.

Plaxis finite element modeling gives the most realistic

results, provided there is correct assumption of volume loss

parameter, which is usually difficult to predict. The model

provides simulation of excavation, lining, grouting and

face pressure in a realistic manner to predict surface and

sub-surface settlements. The volume loss parameter is

usually assumed to be \1% for excavation with face

pressure-balanced tunnel boring machines. The realized

volume loss in the site is around 1% for this study.

Currently, there is difficulty yet in modeling the defor-

mation behavior of twin tunnels. One of the most impres-

sive studies on this issue was performed by Chapman et al.

(2004). However, Chapman’s semi-theoretical method still

requires enlargement of the database to improve the sug-

gested model in his paper.

Conclusions

In this study, three surface settlement prediction methods

for mechanized twin tunnel excavations between Esenler

and Kirazlı stations of Istanbul Metro Line are applied.

Tunnels of 6.5-m diameters with 14-m distance between

their centers are excavated by EPM tunnel boring

machines. The geologic structure of the area can be clas-

sified as soft ground.

Settlement predictions are performed by using FE

modeling, and semi-theoretical (semi-empirical) and ana-

lytical methods. The measured results after tunneling are

compared to predicted results. These indicate that the FE

model predicts well the short time surface settlements for a

given volume loss value. The results of some semi-theo-

retical and analytical methods are found to be in good

agreement with the FE model, whereas some methods

overestimate the measured settlements. The FE model

predicted the maximum surface settlement as 15.89 mm

(1% volume loss) for the right tube, while the measured

Settlement - Heave

Dis

tanc

e fr

om T

unne

l Fac

e (k

m)

Sur

face

Set

tlem

ent -

Hea

ve (

dm)

Distance from Herrenknetch TBM

Distance from Lovat TBM

-0.200

-0.100

0.000

0.100

0.200

5/11

/200

6

5/18

/200

6

5/25

/200

6

6/1/

2006

6/8/

2006

6/15

/200

6

6/22

/200

6

6/29

/200

6

7/6/

2006

7/13

/200

6

7/20

/200

6

7/27

/200

6

8/3/

2006

8/10

/200

6

8/17

/200

6

8/24

/200

6

8/31

/200

6

9/7/

2006

Date

Fig. 10 The effect of the

left tube excavation on

deformations of the right tube

(surface monitoring point no.

25, located on the axis of the

right tube)

Table 5 Summary of predicted

and observed short-term

maximum surface settlements

Prediction method Maximum surface settlement

Plaxis FEM (left tube) 20.22 mm (0.5% volume loss)

24.34 mm (1% volume loss

Plaxis FEM (right tube) 12.35 mm (0.5% volume loss)

15.89 mm (1% volume loss)

Schmidt (1969) and Arioglu (1992) 17.1 mm

Loganathan and Poulos (1998) 23.0 mm

Herzog (1985), right tube 49.9 mm

Herzog (1985), left tube 58.7 mm

Observed (right tube) 9.6 mm average, 15.2 mm maximum

Observed (left tube) 14.4 mm average, 26.3 mm maximum

Environ Earth Sci

123

maximum settlement was 15.20 mm. For the left tube

(opened after the right), FE prediction was 24.34 mm,

while measured maximum settlement was 26.30 mm.

Acknowledgments The authors greatly appreciate the Istanbul

Metropolitan Municipality, IETT, Prof. Dr. Nuh Bilgin and Prof. Dr.

Ergin Arioglu for their valuable support and contributions to the

studies.

References

Arioglu E (1992) Surface movements due to tunneling activities in

urban areas and minimization of building damages. Short

Course, Istanbul Technical University, Mining Engineering

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Attewell PB, Yeates J, Selby AR (1986) Soil movement induced by

tunneling and their effects on pipelines and structures. Chapman

and Hall, New York

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Bilgin N, Ozbayir T, Sozak N, Eyigun Y (2009) Factors affecting the

economy and the efficiency of metro tunnel drivage with two

TBM’s in Istanbul in very fractured rock. ITA-World Tunnel

Congress 2009, Safe tunnelling for the City and for the

environment, 23–28 May, Budapest, Hungary

Chapman DN, Rogers CDF, Hunt DVL (2004) Predicting the

settlements above twin tunnels constructed in soft ground. In:

Shirlaw JN, Zhao J, Krishnan R (eds) Proceedings of the 30th

ITA-AITES World Tunnel Congress, 22–27 May, Singapore

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