Tunnelling Projects in GreeceChallenges,

Experiences & Achievements European Conference on Soil Mechanics

& Geotechnical Engineering Athens GREECE, 12 – 15 / 09 / 2011

ILIAS K. MIHALISCivil Engineer N.T.U.A., MSc, DIC

Outline of presentation• Recent historical background of transportation

tunnelling projects in Greece (period: early 1990’s to the present)

• Gained design experiences related to the excavation and primary support of the tunnels

• Tunnels’ construction challenges in adverse geotechnical conditions

• Unreinforced tunnel final lining – Recent gained design and construction experiences

• Future of tunnelling in Greece• Conclusions

Recent historical background of transportation tunnelling projects in Greece (since early 1990’s until

today)

Network of the major suburban motorway projects

ATTIKI ODOS Athens peripheral motorway project

Athens Metro

Thessaloniki’s Metro

ATHENS

PATRASΚΙΑΤΟ

TITHOREA

LIANOKLADI

DOMOKOS

EVAGELISMOS

LEPTOKARIA

THESSALONIKI

Ν.ΙΚΟΝΙΟ

RAILWAY TUNNELS PATRAS – ATHENS –

THESSALONIKI

The total number of railway tunnels is 93 (52 main tunnels and 41 escape tunnels) with total length 95.680 km

The railway tunnels are single of double direction or twin of single direction with cross escape tunnels. In tunnels of double direction, having length > 1000m, the escape tunnels are constructed at every 1.000 m maximum distance. Special ventilation system has been applied and the tunnels are being checked with telematic systems of high technology.

SKA

Title of the infrastructure Project

Total alignment length (km)

Total tunnels’ length (km)

Egnatia Motorway 670 100Athens – Thessaloniki Motorway 515 35.4Attiki Odos – Athens Peripheral

Motorway65 15.4

Elefsina – Korinthos – Patras – Pyrgos – Tsakona Motorway

365 30.2Korinthos-Tripolis-Kalamata &

Lefktro – Sparti Motorway205 4.9

Ioannina – Antirrio Motorway 159 6Panagia – Lamia Motorway 174 20

Athens Metro 30.4 30.4Thessaloniki Metro 9.5 9.5

Railway / ERGOSE projects 500 95.7

Total length of motorway and railway tunnels for the period:

early 1990’s until today = 347.5km

After Italy, Austria and Germany, Greece has become the fourth country, among all the countries of the European Union, on the basis of the number of the existing motorway tunnels having length > 500m (1).

(1) European Commission, Safety in European Tunnels, PG TREN, Information & Communication Paper, December 2002

Gained design experiences related to the excavation and primary support of

the tunnels

• Geological / Geotechnical mapping of the tunnel face – Geological Strength Index rating system

• Tunnel Stability Factor – An engineering index for the initial assessment of the tunnels geomechanical behavior in weak rocks (i.e. convergences, face instabilities, ground settlements)

Geological Strength Index rock mass rating systemE. Hoek, P. Marinos & M. Benissi (1998, 2000)

Geological Strength Index rock mass rating systemP. Marinos, V. Marinos & E. Hoek (2007)

Geological Strength Index rock mass rating system(Kavvadas’ proposed extension 2004)

Tunnel Stability Factor (I. K. Mihalis, M. Kavvadas & A. Anagnostopooulos, 2001)

Mathematical expression

the rockmass in-situ strength (in KPa)

c the rockmass cohesion (in KPa)φ the rockmass angle of shearing resistance (in degrees)γ the rockmass unit weight (in KN/m3)H the tunnel’s overburden heigtht (m)D the tunnel’s equivalent diameter (m)

aacm

DHTSF 1

sin1cos2

ccm

Tunnel Stability Factor •It is a dimensionless engineering index, followed original Hoek’s proposal (1999) about the adoption of ratio σcm/γΗ, as a controlling parameter of tunnels’ general stability conditions.•It includes the tunnels’ sizes (D), since the practical experience has shown that in even identical geotechnical environments and at the same depth (H), tunnels of different size exhibit deformation modes of different scale and degree of criticality. The more severe tunnelling problems to overcome are related to tunnels with bigger dimensions.

acm

DTSF

1

Tunnel Stability Factor

• The importance of TSF in assessing deep tunnelling conditions and possible shallow tunnelling problems (i.e. Settlements and face instabilities) has been examined through an extensive parametric analyses.

• Parametric analyses were performed mainly with the use of 2-D finite element models and included unsupported circular tunnels with D=4m – 10m, at depths H=10m – 500m, in rockmass conditions characterised by GSI=15 – 50.

acm

DTSF

1

The “governing” role of TSF The “governing” role of TSF, for assessing

both deep tunnelling conditions and any possible shallow tunnelling problems, is clearly presented in the following dimensionless charts. In these charts, all the analyses results tend to follow very similar trends, without significant scattering, despite of the very wide range of the studied tunnelling cases.

Use of Tunnel Stability Factor in assessingdeep tunnelling conditions

u i /r 0 = 0,0053xTSF -1,31

0%1%2%3%4%5%6%7%8%9%

10%11%12%

0,00 0,25 0,50 0,75 1,00 1,25 1,50 1,75 2,00 2,25 2,50

TSF = σ cm /{γΗ 0.75 D 0.25 }

u i/r o

u i /r 0 between 5% and 10% Very severe squeezing

u i /r 0 between 2.5% and 5% Severe squeezing

u i /r 0 between 1% and 2.5% Minor squeezing

u i /r 0 less than 1% Few support problems

Use of Tunnel Stability Factor in assessingdeep tunnelling conditions

0,000,501,001,502,002,503,003,504,004,505,00

0,00 0,25 0,50 0,75 1,00 1,25 1,50 1,75 2,00 2,25 2,50TSF = σ cm /{γH 0.75 D 0.25 }

r p/r o

r p /r 0 =1,79xTSF -0,43

Tunnels’ construction challenges & experiences

1. Athens Metro• Microtunneling in Monastiraki station• Jet Grouting application in Aghiou Konstantinou street

(weathered rock conditions – Athenian shist)

2. Egnatia Motorway• Tunnel S3

3. Maliakos – Kleidi Motorway Concession Project

• Tempi Tunnel T2

Athens MetroMicrotunnelling in Monastiraki

Undergound Station complex

Microtunnelling application

Monastiraki Underground station complex

Monastiraki Underground station complex – Geotechnical conditions

• Weakly metamorphosed mudrock with some meta-siltstone / sandstone horizons. Extensive shears exist in the original mudrock material. The whole formation is intensively disturbed, that finally it is characterized by numerous discontinuities, randomly spaced and oriented shears. Additionally the formation’s weathering is extensive.

• Very “poor”geotechnical conditions, which created skepticism about the safety of the needed excavations, and their impact on to the structural integrity of the numerous old buildings at the surface.

• The major and challenging engineering problem was the control of the unavoidable surface settlements, caused by the excavations, in acceptable limits, without triggering the existing serviceability conditions of the building at the surface.

Monastiraki Underground station complex – In situ geomechanical properties of the

mudrock

Monastiraki Underground station complex – Microtunnelling application

Athens MetroJet Grouting application in Aghiou

Konstantinou street (weathered rock conditions)

I. K. Mihalis, G. Tsiambaos & A. Anagnostopoulos (2004)

Jet Grouting area

Tunnel Boring Machine

Tunnel face collapses during TBM operations in Aghiou Konstantinou street

1. Description of collapses:: Non - controllable face collapses at the TBM cutterhead

2. Causes of collapses:• Poor cohesion characteristics of the ground• Existence of ancient man-made cavities (i.e. wells),

usually back-filled with rubble and mud, reaching to the tunnel crown

3. Effects of ground collapses:::• Excessive settlements at the surface (in some cases

surface collapses)• Buildings damages due to differential settlements• Serious delays in the progress of the Project

Surface collapses during TBM operations

Ground conditions in the areas of overbreaks and excessive settlements –

Aghiou Konstantinou street

• Overburden layer of alluvial deposits and backfill materials: Brownish sandy, silty clay with occasional fragments of limestone and siltstone. Thickness: 2m - 6m.

• First horizon of the Athenian schist: Greenish – greyish fractured weak meta-siltstone with medium to high degree of weathering. Thickness: 4m - 8m.

• Second horizon of the Athenian schist: Greyish - black highly weathered very weak phyllite & fractured very weak meta-siltstone.

The philosophy of the groundpre-treatment by jet grouting along Aghiou

Konstantinou street Typical cross-section with

jet grouted columns• Diameter of jet grouted

columns 60cm.• Double water cut jet grouting

(without water pre-cutting) was used.

Length of treated area ~ 190m

Depth of the tunnel’s crown ~ 12m

Application & Evaluation of jet grouting trials

1. Tested jet grouting techniques• Single jet grouting• Double water cut jet grouting, with and without pre-

cutting.• Triple jet grouting2. Evaluation of the tested jet grouting techniques

through the Specific Jet Grouting Energy EsEs = (PxQ/Vt)grout+(PxQ/Vt)water (MJ/m)

where: P : grout or water pressure (in MPa) Q: grout or water flow rate (in m3/h)

Vt: withdrawal speed (in m/h).

Evaluation of Jet Grouting Trials in Aghiou

Konstantinou area (Athenian Schist conditions)Jet Grouting Trial Tests

Specific Jet Grouting Energy vs Grouted column's diameter

0

20

40

60

80

100

120

140

160

30 40 50 60 70 80 90 100 110 120 130Grouted column diameter D (cm)

Spec

ific

Jet G

rout

ing

Ene

rgy

Es

(MJ/

m)

Single Double WC Double WC + prec. Triple Es (MJ/m)

E s=0.0101xD 2.02

Maximum recorded settlements along Aghiou Konstantinou after jet grouting pre-treatment

Maximum Settlements and relative ground losses (after the pre-treatment)

0.00

0.01

0.02

0.03

0.04

0.05

Chainage

surf

ace

sett

lem

ent (

m)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

surf

ace

rela

tive

grou

nd lo

ss (%

)

Maximum settlement Relative ground loss

Area A40% Soil Replacement

Area B25% Soil

Replacement

Egnatia Odos Motorway Tunnel S3

Location of Tunnel S3

Panoramic view of Tunnel S3

Characteristics of Tunnel S3

•Shallow twin bored hill-slope tunnel. The slope has a mild inclination 200 parallel to the tunnel axis•Tunnel’s length = 230m•Tunnel’s width = 12m•Axial spacing between the bores = 30m•Maximum overburden height Hmax=30m

Problems encountered during underground excavations

• Slope translation movements downhill, initiated with the tunnel excavation and continued even during the stoppage of the excavations

• High displacements • Cracks of the temporary

support shell (temporary invert)

• Cracks on the ground surface upstream of the hill

Geological & Geotechnical conditions• Highly tectonised alterations of thin-bedded to

mid-bedded limestones and argillaceous phyllites. No groundwater at the excavations’level

• Entrance portal area: Higlhy weathered phyllites dominate. Soil – like behavior

• Exit portal area: Better quality phyllites dominate• General conclusion: The geological formations

are of poor quality. Especially the surface formations are in limit post-equilibrium situation, marginal meta-stability conditions

Monitoring results

i. The tunnel total displacements at the exit portal (~6cm to 8cm) were significantly lower than those at the entrance portal (~ 30cm to 40cm)

ii. The maximum recorded surface movements above the two tunnel bores were at the order of 25cm to 30cm

Μετακινήσεις κλείδας δεξιού κλάδου

0

50

100

150

200

250

300

350

400

Χιλιομετρική θέση

Μετ

ακίν

ηση

σε

mm

μετακίνηση κατά xμετακίνηση κατά z

The solution for the stabilisation

Maliakos – Kleidi Motorway Concession ProjectTempi Tunnel T2

Location of Tempi Tunnels T1, T2 and T3

Characteristics of Tempi Tunnel T2• Two - bound tunnel: South bound L=5.94Km and

North bound L=5.95Km• According to the traffic & safety requirements the

tunnel’s cross-section is comprised by 2 traffic lanes (3.75m width) and an emergency lane (2.50m width). Consequently the maximum excavation dimensions are: 15m (width) and 13m (height)

• Maximum Overburden height Hmax= 285m• Distance between the two bounds axes = 25m• Until now Tempi tunnel T2 is the longest

motorway tunnel in Greece and the Balkans

Problems encountered during underground excavations

• Continuous major face collapses,• Serious, early and long term squeezing

phenomena and • Strong interaction between the two bounds were encountered during the underground

excavations, along a zone of 60m in length, comprised by severely tectonised phyllites.

• The overburden height along the problematic zones did not exceed 70m.

Tectonised phyllites• Grey coloured

geomaterials, completely fractured and sheared, crossed by faults and contacts

• Hard soil – like behavior

• The orientation of the quasi-schistosity planes was unfavouable to the excavation

Tunnel face collapses

Serious early and long term squeezing during top – heading excavation

Immediate contingency measures

“Pilot tunnel” solution

Unreinforced tunnel final lining – Recent gained experiences

The Unreinforced concept of the tunnel final lining

• The existing design and construction experience in tunnelling show that it is not a prohibitive concept

• It is imperative need the understanding of the necessary limits of its application

• Limits are related to the geotechnical environment, the seismic / tectonic regime and the topography in direct relation to the safety and the serviceability limits of behavior of the tunnel structure

Existing relevant Codes, Recommendations and Design Guidelines

• Eurocode EN-1992-1/Section 12 Plain and Lightly Reinforced Concrete Structures

• German DAUB Recommendations for Executing and Application of Unreinforced Tunnel Inner Linings

• French AFTES Recommendations in Respect for the Use of Plain Concrete in Tunnels

• Design Acceptance Criterion: Cracks (of limited depth & width) are allowed to form, as long as they don’t affect safety & serviceability of the structure

e.g. AFTES: Crack depth < H/2 if axial force N>2.7% of failure axial force in compression (b·h·fcd)

Estimation of cracking development in competent rockmass conditions E=1GPa

1

ANSYS 9.0CRACKS AND CRUSHING

STEP=1SUB =10TIME=1

1

ANSYS 9.0CRACKS AND CRUSHING

STEP=1SUB =10TIME=1

-12 -10 -8 -6 -4 -2 0axia l stress (M Pa)

E=1GPa

ANSYS 9.0CRACKS AND CRUSHING

STEP=1SUB =15TIME=1

X

Y

Z

ANSYS 9.0CRACKS AND CRUSHING

STEP=1SUB =15TIME=1

E=300MPa

Estimation of cracking development in “poor” rockmass conditions E=300 MPa

-12 -10 -8 -6 -4 -2 0axia l stress (M Pa)

E=1GPa

Seismic Design Numerical Analyses

E=300MPa

2-D dynamic analyses → effect of topography, stratigraphycalculation of N,M time histories on the final lining

use of AFTES Recommendations for the verification

The future of tunnelling in Greece

• Extensions of Athens and Thessaloniki metros

• Extension of Attiki Odos (Athens peripheral motorway) to the south suburbs of Athens

• New Railway lines (i.e. West axis, Thessalia – Epirus link, completion of Patras – Athens – Thessaloniki line)

• Tunnels of the gold mines project in North Greece ( ~ 35 to 40 km)

Conclusions• The last 20 years can be considered as

the “ tunnelling golden age” for Greece

• The most significant achievement is that numerous real difficult tunnelling projects were finalized on time and within reasonable cost budgets

• Especially tunnelling in the framework of the new concession projects provided to the greek engineers with real “value engineering” skills

Conclusions• The gained design and construction

experiences in dealing with weak, heterogeneous geological formations are ready to be transferred to a number of new similar tunnelling projects in abroad

• The future of tunnelling in Greece is promising, although the very tough financial crisis

ACNOWLEDGEMENTS• The Organizing Committee of the Conference

(Prof. Anagnostopoulos, Dr. Tsatsanifos, Mr. Vettas, Mr. Pachakis and Mr. Doulis)

• OMIKRON KAPPA (Dr. Koronakis & Dr. Kontothanassis

• ERGOSE S.A. (Dr. Yiannis Petropoulos & Dr. Kapenis)

• ATTIKO METRO S.A.• Professor Michael Kavvadas• Dr George Kouretzis• SALFO & Associates S.A. ( Mr. G. Salpeas and

I. Fotinos)

THANK YOU VERY MUCH FOR YOUR ATTENTION