ilias michalis pmv workshop dubai 2014

Evaluating the application limits of Unreinforced & Steel Fiber Reinforced Concrete (SFRC) for tunnel final linings

Ilias Michalis, MSc, DICTechnical Manager Underground Works, Qatar Rail

Dr. Petros FortsakisTunnel Expert, Qatar Rail

Konstantinos Seferoglou, MScGeotechnical Expert, Qatar Rail

Dr. Zheng HuangTunnel Expert, Qatar Rail

https://www.db-international.de


OUTLINE OF THE PRESENTATION 1. Recent tunnel cases with unreinforced and Steel Fiber Reinforced

Concrete tunnel linings2. Existing Design Codes and Design Recommendations framework3. Numerical analyses of the unreinforced concrete tunnel linings under

static and seismic loading conditions. T1 & T2 tunnels of Maliakos - Kleidi Motorway and T26 tunnel of Athens - Patras Motorway in Greece.

4. Numerical analyses of SFRC tunnel linings under static loading conditions.

5. Some critical thoughts about the geostatic loads on to the tunnel final linings.

6. Some critical thoughts about the ground elastic modulus for the design of tunnel linings

7. Conclusions

The existing design and construction experiences in tunnelling worldwide gives the answer:

NO

1. ARE THE CONCEPTS OF THE UNREINFORCED & STEEL FIBER REINFORCED CONCRETE TUNNEL FINAL LININGS PROHIBITIVE ONES?



Tunnel Country Type of tunnel

Completion time

Length(km)

Tunnel section

(m2)

Final lining

thickness (cm)

Brief geology

Tradenberg Switzerland Motorway 2009 2 126 40 Mudstones, Sandstones, Clay marls

Grouft Tunnel Luxembourg Motorway 2010 3 96 Marls, Sandstones

Gotthard - Base Tunnel

Switzerland Railway On going 25 65 30 - 40 Gneiss

Loetschberg Tunnel

Switzerland Railway 2008 35

Schwarzer berg Tunnel

Germany Motorway 2004 1 102 30 - 40 Gypsum

CTRL 104 North Downs

Tunnel

U.K. Railway 2002 3 103 35 - 40 Chalk

RECENT TUNNELS WITH UNREINFORCED CONCRETE TUNNEL FINAL LININGS



Completion time

Length(km)

Tunnel section (m2)

Final lining

thickness (cm)

Brief geology

Aesch Tunnel Switzerland Motorway 2.3 135 35 - 40 Molasse rocks

Rennsteigtunnel

Germany Motorway 2001 8 80 - 120 30 Sandstones, Siltstones,

Conglomerates

Tempi Tunnel T1

Greece Motorway 2014 1.8 120 45 Marbles and Amphobolites

Tempi Tunnel T2

Greece Motorway 2014 6 120 45 Amphibolites Marbles with

phyllites intercalations

Panagopoula Tunnel T26

Greece Motorway On going 4 100 40 Limestones, Cherts and

Conglomerates

RECENT TUNNELS WITH UNREINFORCED CONCRETE TUNNEL FINAL LININGS



Completion time

Length(km)

Tunnel section (m2)

Final lining

thickness (cm)

Brief geology

CTRL (Connection to

St. Pancras Station)

U.K. Railway 2004 2 40.2 35 London Clay

Oenzberg Tunnel Switzerland

Railway 2003 3.16 102.7 40 Molasse

Hofoldinger Stollen tunnel

Germany Hydraulic 2004 17.5 8.6 18 Hard Conglomerate

sSTEP

(Strategic Tunnel enhancement Programme)

U.A.E (Abu Dhabi)

Hydraulic 2012 15.6 31.2 28 Claystones & Mudstones SiltstonesGypsum

Barcelona Metro (Line 9) - Can Zam

stretch

Spain Railway 2003 3.9 93.3 35 Granodiorites

RECENT TUNNELS WITH STEEL FIBER REINFORCED CONCRETE TUNNEL FINAL LININGS


Tunnel Country

Type of tunnel

Completion time

Length(km)

Tunnel section (m2)

Final lining

thickness (cm)

Brief geology

Sao Paulo Metro (Line 4)

Brazil Railway 2009 1.2 55.4 35 Weathered Gneiss

Clem Jones Tunnel Australia Motorway 2010 4.8 102 40 Volcanic Ash Metamorphic

rocksGold Coast

Desalination TunnelsAustralia Hydraulic 2008 (planned) 4.2 9.1 30 Sandstones &

Mudstones

RECENT TUNNELS WITH STEEL REINFORCED CONCRETE TUNNEL FINAL LININGS


Unreinforced concrete tunnel linings were successfully constructed for tunnels of large cross sections and in different ground conditions.

Rennsteig tunnel presently is the longest Motorway tunnel in Germany (length ~ 8km).

Tempi Tunnel T2 presently is the longest Motorway tunnel in the Balkans region (length ~ 6km).

In CTRL 104 North Downs Tunnel, the unreinforced lining is considered as a real “value engineering” solution resulted to £10m savings in the budget and completion time 5 months ahead of the Project’s schedule.


Steel fiber reinforced concrete tunnel final linings have been successfully constructed mainly in railway tunnels of cross sections between 40m2 to 90m2.

Thickness of the Steel fiber reinforced concrete tunnel final linings in railway tunnels varied between 35cm 45cm.

Barcelona Line 9. “Mixed” concept of steel fibers and traditional steel reinforcement was applied.

Clem Jones Tunnel currently is the longest motorway tunnel in Australia (4.8 km).

STEP is the first application of the steel reinforced concrete concept in segmental linings in the GCC countries.

Major issues to be considered for the successful application of the concepts: Application limits of the concepts must be derived. These Application limits are related to:

• The geotechnical environment (e.g. ground stiffness & acting overburden geostatic load)

• The seismic / tectonic regime • The topography

of every tunnel location The Application limits are related to well determined safety and serviceability

requirements of the unreinforced & steel reinforced concrete tunnel final lining behaviors.

The Design and Construction must fulfill these requirements.https://www.db-international.de

Major issues to be considered for the successful application of the concepts: The Safety and Serviceability Requirements of the unreinforced

and SFRC tunnel final linings behaviors are described in existing Design Codes and Design Recommendations.

Realistic cost-effective in situ concrete construction solutions, which prevent from the formation of the initial cracking, caused during the temperature cycle: “Dissipation of the hydration heat and subsequent shrinkage”.


Main advantages and material properties of steel fiber reinforced concrete: Ductility in tension and in compression Impact resistance High resistance against spalling Increased Durability Low crack widths under service conditions Flexural strength in all three directions


Applications & Effectiveness of steel fiber reinforced concrete in segmental linings Steel fiber reinforced concrete segmental linings can be used for

loading cases, which result to high compressive forces and relatively low bending moments.

There are no costs from the provision and storage of reinforcement cages.

No reinforcement works is necessary, thus the working process is accelerated.

In case of cracking, load transfer across the crack is assured. Load bearing capacity of steel fiber reinforced concrete segmental lining is ensured.

The increased ductility of the steel fiber reinforced concrete in segmental linings results to lower “absorbed” forces.









7. Conclusions

Relevant Codes, Standards, Guidelines & Recommendations Eurocode 2 EN 1992 - 1 / Section 12: Plain and lightly reinforced

concrete structures AFTES Recommendations in respect of the use of plain concrete in

tunnels (e.g. crack depth and loads eccentricity limits) Rudolf Pottler publication: “The unreinforced inner lining of rock

tunnels - stability analysis and deformation of the crack area” (e.g. crack width estimation)

DAUB Recommendations for executing and application of unreinforced tunnel inner linings

FIB Model Code for Concrete Structures 2010



Eurocode 2 EN 1992 - 1 / Section 12: Plain (unreinforced) and lightly reinforced concrete structures


Eurocode 2 EN 1992 - 1 / Section 12: Plain (unreinforced) and lightly reinforced concrete structuresConcrete additional design assumptions (Clause 12.3.1):

1.Design compressive strength: fcd = acc,pl(fck/γc)2.Design tensile strength: fcd = acc,pl(fctk,005/γc)where: acc,pl & act,pl = 0.8, due to the less ductile properties of plain concretefck is the characteristic compressive strength of concretefctk,0.05 is the characteristic axial tensile strength of concrete andγc =1.50 for persistent and transient actions, 1.20 for accidental actions


Eurocode 2 EN 1992 - 1 / Section 12: Plain (unreinforced) and lightly reinforced concrete structuresConcrete additional design assumptions (Clause 12.3.1):3. Tensile stresses can be considered

in the design, by extending linearly the stress- strain diagram of concrete into the tensile region, up to the design tensile strength fctd


Eurocode 2 EN 1992 - 1 / Section 12: Plain (unreinforced) and lightly reinforced concrete structuresVerification Criteria at the Ultimate Limit States are described in Clause 12.6:Clause 12.6.1 describes the design resistance to bending and axial force:Computed axial force N < NRd = fcd × b × hw × (1-2e/hw)fcd is the concrete design compressive strengthNRd is the ultimate axial force,b is the overall width of the lining sectionhw is the overall thickness of the lining section and e is the load eccentricity

No limit to acceptable crack

depth


Eurocode 2 EN 1992 - 1 / Section 12: Plain (unreinforced) and lightly reinforced concrete structuresVerification Criteria at the Ultimate Limit States are described in Clause 12.6:Clause 12.6.3 describes the design resistance to shear:For a tunnel lining section subjected to a shear force V and an axial force N, acting over a compressive area Acc, then:the shear component of design stress τcp = 1.5(V/Acc) ≤ fcvd

where fcvd is the concrete design strength in shear and compression


AFTES Recommendations in respect to the use of plain concrete in tunnelsVerification Criteria at the Ultimate Limit State (based on Eurocode 2):Design resistance to bending and axial force. If the computed axial forces N < NRd0 = 0.027(fck × b × hw), NO particular check is needed.fck is the characteristic compressive strength of concrete, b is the overall width of the lining section and hw is the overall thickness of the tunnel lining section


Verification Criteria at the Ultimate Limit States (based on Eurocode 2)Design resistance to bending and axial force. If the computed axial forces N>NRd (ultimate axial force), then Reinforcement MUST be provided or Redesign of the section is NECESSARYNRd = 0.57 × fck × b × hw (1-2e/hw) (basic ULS) NRd = 0.74 × fck × b × hw (1-2e/hw) (accidental ULS)Load eccentricity e = (M / N), M is the computed bending moment

AFTES Recommendations in respect to the use of plain concrete in tunnels


Verification Criteria at the Ultimate Limit State (based on Eurocode 2)Design resistance to bending and axial force.If the computed axial forces NRd0 < N<NRd then:Load eccentricity e=M/N > 0.3 × hw Load eccentricity e=M/N < 0.3 × hw

AFTES recommends the limitation of the load eccentricity: e< 0.3xhw and imposes the crack depth limitation to the ½ of the unreinforced tunnel lining thickness (major serviceability criterion for the unreinforced concrete tunnel final linings)

Unreinforced: UNACCEPTABLEUnreinforced: ACCEPTABLE

AFTES Recommendations in respect to the use of plain concrete in tunnels


Serviceability criterion of the unreinforced concrete tunnel final linings related to the maximum accepted crack width (Pottler’s publication)


DAUB - German Recommendations for executing and application of unreinforced Tunnel final (inner) linings DAUB attempts to restrict the application fields of unreinforced

tunnel final linings, due to high possibility of cracking, as an effect of their low tensile strength.

According to DAUB, unreinforced tunnel final linings are suitable for blocks of standard geometry in road tunnels, provided that these are located in solid rocks and not in excessive depths.


DAUB - German Recommendations for executing and application of unreinforced Tunnel final (inner) liningsDAUB proposes: Unreinforced tunnel linings can be executed at maximum block

lengths of 12m to 12.5m. For road and railway tunnels, the minimum thickness of

unreinforced tunnel linings is 30cm. Smaller thicknesses are possible for relative smaller tunnel sections.


DAUB - German Recommendations for executing and application of unreinforced Tunnel final (inner) liningsDAUB proposes: Suitable concrete mixes, which restrict the maximum

temperature during the setting process, but result to short stripping periods. • Cement / fly ash combinations are advantageous.• The addition of hard coal fly ash reduces the hydration heat

effect, improves processability, diminishes the danger of demixing and caters for a denser concrete texture.


FIB Model Code for Concrete Structures 2010 Significant relevant clause for FRC: Clause 5.6

“……Structural design of FRC elements is based on the post-cracking residual strength provided by fibre reinforcement….Fibres can be used to improve the behavior at SLS since they can reduce crack spacing and crack width, thereby improving durability. Fibres can be used to improve the behavior at ULS where they can partially or totally substitute conventional reinforcement……”

Fiber reinforced concrete structures


Behavior in compression: Generally the compressive relations valid for plain concrete also apply to FRC.



Behavior in tensionNominal values of the material properties can be determined by performing a three-point bending test on a notched beam according to EN 14651.


Fj[N]: load corresponding to CMOD = CMODjCMOD: crack mouth opening displacement


Behavior in tensionNominal values of the material properties can be determined by performing a three-point bending test on a notched beam according to EN 14651.


Fj[N]: load corresponding to CMOD = CMODjCMOD: crack mouth opening displacement

fR1

fR3


Classification• Characteristic flexural strength, serviceability conditions: fR1k

• Characteristic flexural strength, ultimate conditions: fR3k

• Example of FRC class: 4cThe first number “4” defines the minimum value fR1k: 4MPaThe letter “c” defines the ratio the range of the ratio fR3k/fR1k


a: 0.5 < fR3k/fR1k < 0.7b: 0.7 ≤ fR3k/fR1k < 0.9c: 0.9 ≤ fR3k/fR1k < 1.1

d: 1.1 ≤ fR3k/fR1k < 1.3e: 1.3 ≤ fR3k/fR1k

Limit of Proportionality:


Classification• Characteristic flexural strength, serviceability

conditions: fR1k

• Characteristic flexural strength, ultimate conditions: fR3k

• Example of FRC class: 4cThe first number “4” defines the minimum value fR1k: 4MPaThe letter “c” defines the ratio the range of the ratio fR3k/fR1k

• Fibre reinforcement can substitute (also partially) conventional reinforcement at ultimate limit state, if the following relationships are fulfilled: fR1k/fLk>0.4, fR3k/fR1k>0.5.



Partial safety factors for FRC strength• Design Compressive strength: As plain concrete, fcd = fck / γc

• Design Tensile strength (limit of linearity): As plain concrete, fctd = fctk / 1.5

• Design Tensile strength (residual strength): γF=1.50Design Serviceability residual tensile strength fFtsd = fFtsk / γF = f(fR1k)Design Ultimate residual tensile strength fFtud = fFtuk / γF = f(fR3k)



The design of FRC structures is a challenging procedure since some of the design parameters are not determined via the relevant codes, but using results of laboratory tests.

It is critical to choose the concrete mix and carry out the laboratory tests in the initial stages of the design to calculate / verify all the design strength values.

In tunnelling it is useful to carry out a sensitivity analysis for anticipated range of the geotechnical parameters to determine the limitations of this design approach.









7. Conclusions


Located in North Greece Two bore NATM tunnel with cross

section 120m2. Length = 6km Geological conditions: Marbles and

Amphibolites (mostly competent rock mass conditions)


Numerical parametric analyses – Static conditions Eurocode Part1-1/Section 12 and AFTES

recommendations for plain concrete were adopted

3-D non-linear Finite Element code was used

Willam & Warnke constitutive model to simulate concrete response (cracking and crushing) was adopted

Basic Ultimate Limit States (for different load cases and lining types) were calculated

The numerical parametric analyses examined the effect of the in-situ rockmass properties on to the linings response


Willam & Warnke Unreinforced concrete constitutive model (1975)Major advantages of the model: Simulate concrete non-linear stress-

strain response, as well as concrete cracking/crushing in three-dimensions.

Adopts different strength values in compression and in tension.

Accounts directly lining stiffness degradation due to cracking.However it requires very fine 3D finite element mesh (element size ≈0.05m).

octahedral plane

σ x=σ y=σ zr1

r2

r2

r2

r1

r1 n

σ z

fcd

σ x

fcd

σ y

fcd


Properties of the Unreinforced Concrete used in Willam & Warnke constitutive modelSummary of C30/37 properties according to Eurocode 2


Numerical simulation of concrete tunnel lining - geomaterials interaction“Stick-slip” elastic springs

Force

D isp lacem ent

K i

compression

tension

Ki values = f(rockmass, lining

geometry)


Final Lining Type

Load Case Description

Rockmass modulus

of deformation

Maximum rockmass load

LC11 temperature

1000MPa

0

LC13 rockmass+temperature 180KPa

LC100 de-moulding stage 0LC31 explosion 0LC11 temperature

300MPa

0

LC13 rockmass+temperature 220KPa

LC100 de-moulding stage 0LC31 explosion 0

Examined ULS cases

1

ANSYS 9.0ELEMENTS

ANSYS 9.0ELEMENTS


Examined ULS casesAdditional parametric analyses for closed tunnel section: Uniform face conditions: Erockmass = 150MPa, 800MPa Mixed face conditions: Erockmass (vault / invert) = 150MPa /

800MPa, 800MPa / 150MPa Maximum rockmass load 220KPa


Estimation of cracking development in competent rockmass conditions E=1GPa - Rockmass load case


Estimation of cracking development in competent rockmass conditions E=1GPa - Rockmass load case

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


Estimation of cracking development in competent rockmass conditionsE=0.3GPa - Rockmass load case


δmax=2.39cm

δmax=4.56cm

Open tunnel section

Erockmass=1 GPa

Tunnel section with closed invert

Erockmass=0.3GPa

Tunnel linings - Calculated deformed shape under rockmass loadings








7. Conclusions


Eurocode Part1-1/Section 12 and AFTES recommendations for plain concrete were adopted. Seismic actions resulting in low axial forces did not require an eccentricity check (no restrictions in crack depth).

Eurocode 8 EN-1998 was used to determine seismic actions, concrete properties, factors of safety for the accidental load case etc.

Competent limestone conditions E = 1GPa and irregular topography were examined.


2-D Dynamic numerical analyses


2-D Dynamic numerical analyses Eccenticity check according to AFTES (Erockmass = 1GPa)Results in critical points

along the tunnel cross-section

Zone of high axial force requirement for low eccentricity (crack control)

Conclusion: In competent rock mass conditions (E=1GPa), an unreinforced lining may be sufficient, even in areas of high seismicity








7. Conclusions


AssumptionsStructural models used to simulate the ring and the ground

A 3d shell elements supported by non linear springs to simulate the

ground

A simple linear beams on non linear springs to simulate the

ground


Assumptions Consideration of “full” overburden load (no “arching”) Concrete parameters

• Concrete category: C50/60• Design compressive strength fcd=0.85×fck/γc, γc=1.50• Design tensile strength fctd=fctk,0.05/γc, γc=1.50

Numerical model• Beam elements on springs & shell elements on springs• Non linear bedding (springs) with zero tensile strength• Normal bedding value: C=Erockmass/R, Tangential bedding value:

Ct=0.1Cwhere R: Tunnel radius

-10000

-8000

-6000

-4000

-2000

0

2000

-400 -200 0 200 400

M (kNm/ m)

N (k

N/m

)


Investigation of the tunnel’s ring response – Full overburden approachLoad assumption 1 Load assumption 2


Investigation of the tunnel’s ring response – Full overburden approach Bending moment (M)

Load assumption 1

Load assumption 2

Normal forces (N) Bedding springs


Parametric analyses with full overburden approach - Unfavorable load combination in ULSLoad assumption 1C50/60, d=0.30m

Maximum overburden height H vs Eground and Ko


Comparison of the two loading assumptions

Upward pressure applied on the tunnel invert

NO upward pressure applied on

the tunnel invert


Load assumption 1 “+” Application of grouting pressure Maximum overburden height for SFRC concept vs Eground and Ko

For Erockmass < 1GPa, the grouting pressure is beneficial, since the overburden height (for which SRFC concept is applicable) increases

For Erockmass ≥1GPa, the grouting pressure has no benefit








7. Conclusions


The ground load applied on the tunnel lining is not a “property” of the ground - as it is assumed by the empirical methods - but depends very significantly on the construction procedure and the applied support measures.

The parameters that must be taken into account for the calculation of the tunnel load are:• Rock mass strength and stiffness parameters• Tunnel depth• Dimensions and shape of the tunnel section• Construction procedure (full face, sequential excavation etc.)• Support stiffness and distance of the support from the tunnel face• Face pressure or face treatment measures (forepolling, fiberglass

nails etc.)• Rock mass creep


The role of the geotechnical conditions (Fortsakis 2012)

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00TLF = (σ c/po )0.3 (ED/Eshdsh)0. 7

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

Μέσ

η π

ίεση

/ Μ

έση

γεω

στατ

ική

τάση

p m /

p o,m

Άνω όριο

Κάτω όριο

m1.80 1.800.30 0.70o,m

co sh sh

p 1.40 p 1.40p 0.50(1 K)γΗ(0.5TLF 1.85) σ ED0.5 1.85p E d

Conventional methodHoek-Brown materialsFortsakis (2012)

Aver

age

tunn

el lo

ad /

mea

n ge

osta

tic

stre

ss

TLF = ( σc / po )0.3 ( ED / Eshdsh )0.7

0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

σc / po,m

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

1.10

1.20

p FL,

m /

p sh,

m

dsh = 20cm , dFL = 60cm

dsh = 40cm , dFL = 40cm


Load transfer from temporary support to final lining (NATM method)

po,m=0.5(1+K)γΗσc=2∙c∙tan(45+φ/2)

pFL,m: Final lining average loadpsh,m: Shotcrete average load

Fortsakis et al. (2014)








7. Conclusions


The use of F.E. analysis has become widespread and popular in tunnelling, as means of controlling and optimizing design tasks

F.E method is extremely powerful in stress - strain predictions The quality of any stress - strain prediction (with F.E methods)

depends on the adequate model being adopted (rockmass constitutive model)

More realistic prediction of rockmass movements requires the adoption of a non-linear stress - strain relation, before reaching the ultimate state

Non-linear elasticity, characterized by strong variations of rockmass stiffness, which depend on the magnitude of strain levels occurring during construction stages


In tunnelling design, pre-failure rockmass stiffness plays a crucial role in predicting the complete behavior of tunnels and their surrounding rockmass in Serviceability Conditions

Characteristic Rockmass stiffness (G) vs shear strain curves must be derived

These curves can be determined on the basis of reliable and accurate in-situ testing and conventional laboratory testing

In situ testing methods: Seismic & Geophysical methods, Dilatometer tests(DMT), Pressuremeter tests (PMT)

Conventional laboratory testing: UCS with stiffness measurement


Typical representation of rockmass stiffness variation as a function of the shear strain amplitudes

Proposed Rock mass stiffness value measured in dilatometer tests and in the initial loading cycles of pressuremeter tests.

Proposed Rock mass stiffness value at the range of shear strain: 0.5x10-3 to 10-3.

ROCK MASS STIFFNESS FOR

TUNNEL DESIGN IN SERVICEABILITY

CONDITIONS









7. Conclusions


CONCLUSIONS The concepts of the unreinforced and steel fiber reinforced concrete

tunnel final linings are not prohibitive During the recent years, a significant number of motorway and

railway tunnels with unreinforced and steel fiber reinforced concrete tunnel final linings have been constructed successfully

Eurocode 2, EN 1992-1 / Section 12 and AFTES Recommendations, provide the necessary design code framework for the design of unreinforced concrete tunnel final linings

Fib Model 2010 (Design Code since November 2013) can be used for the design of steel reinforced concrete tunnel final linings


CONCLUSIONS The structural integrity of the unreinforced concrete tunnel linings

has been verified for the case of competent rock masses with Em > 800MPa - 1000MPa, even in areas of high seismicity and irregular topography

Unreinforced concrete tunnel linings in rock masses with 300MPa < Em ≤ 800MPa may exhibit significant cracking, in combination with spalling.

Unreinforced concrete tunnel linings of typical thickness 30cm to 40cm in rock masses with Em ≤ 300 MPa are characterized by high risk of concrete crushing. Must be avoided

At tunnel portals, as well as in areas of nearby or crossing active faults, the unreinforced concrete tunnel linings must be avoided


CONCLUSIONS The design of FRC structures is a challenging procedure since some

of the design parameters are not determined via the relevant codes, but using results of laboratory tests.

It is critical to choose the concrete mix and carry out the laboratory tests in the initial stages of the design to calculate / verify all the design strength values.

In tunnelling it is useful to carry out a sensitivity analysis for anticipated range of the geotechnical parameters to determine the limitations of this design approach.


CONCLUSIONS Steel fiber reinforced concrete tunnel final linings of typical thickness

between 30cm to 35cm in rock masses with Em ≥ 800 MPa can be safely applied, even with the consideration of full geostatic load for overburden heights ≤ 30m.

Steel fiber reinforced concrete tunnel final linings in rock masses with 500MPa< Em< 800 MPa can be safely applied, even with the consideration of full geostatic load for overburden heights ≤ 20m.

In rock masses, which are characterized by high shear strength and stiffness, tunnel final lining loading conditions are significant lower than the ones of the initial geostatic stress field.


CONCLUSIONS The use of face treatment measures or the application of face

pressure may lead to increase of the final lining loads due to the decrease of the deconfinement.

In conventional tunnelling the load transfer from the temporary support to final lining depends on the stiffness of the support systems and the geotechnical conditions.

The interaction between twin tunnels may lead to increase of the applied loads and to an unsymmetrical load distribution.

Rock mass stiffness value at the range of shear strain: 0.5x10-3 to 10-3 (from in-situ dilatometer and pressuremeter testing results).


ACKNOWLEDGEMENTS Qatar Rail and specifically Mr. Daniel Leckel, Chief of Program

Delivery Dr. George Kouretzis, University of Newcastle in Australia Deutsche Bahn International and specifically Mr. Michael Ahlgrimm,

Executive Director of Doha branch Mr. Carsten Schulte of Hochtief Offshore Development Solutions

GmBH Dr. Isavella Vassilopoulou, Civil Engineer N.T.U.A.

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