Steel Fiber Reinforced Concrete (SFRC) for TBM Tunnel Segmental Lining Case Histories in the Middle East. 1 Ing. Guido Castrogiovanni, COWI

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1 Steel Fiber Reinforced Concrete (SFRC) for TBM Tunnel Segmental Lining Case Histories in the Middle East 1 Ing. Guido Castrogiovanni, COWI

COWI COWI BTM participates in some of the world s landmark projects such as the largest offshore wind farms, deepest immersed tunnels, challenging metro-projects, longest bridges and most complex

2 COWI COWI BTM participates in some of the world s landmark projects such as the largest offshore wind farms, deepest immersed tunnels, challenging metro-projects, longest bridges and most complex marine structures. 2 Working in 24 countries and 97 international offices Approx. 6,200 employees World-class competencies within engineering, economics and environmental science At any given time, 13,000 ongoing projects 85 years of history

3 COWI SCFR Experiences Red Line North Underground, Doha QA Abu Hamour Sewer, Doha QA STEP Project, Abu Dhabi UAE 3

4 Why the SFRC should be used (or not) for segmental lining? This presentation refers to tunnels in which 80%- 90% of the precast segments rings are reinforced with Steel Fibers and the remaining rings with traditional rebar cages. The SFRC is loved by Contractors. Corrosion and life service: The SFRC solved easily most of the corrosion issues within the design of precast segmental linings. The fibers reduces the local damages (corners), and severity of cracks in given conditions. 4

5 Why the SFRC should be used (or not) for segmental lining? Fire protection: The expected spalling will be reduced Stray current: is definitely solved Sustainability: the steel reinforcement volume is significantly reduced 5

6 Why the SFRC should be used (or not) for segmental lining? The SFRC is not loved by some Agencies/Client. The technology is not fully known by the market. Difficult approval process. The design phase is critical, additional risk. The SFRC requires additional tests to define the SFRC strength. The SFRC requires the contractor capability for the concrete mix and the ring assembling. Some kind of cracks are critical with the fibers. 6

SFRC Lining in Middle East Tunnels COWI designed 3 different SSFRC lining tunnels with diameters variable from 4 to 6m (check) in different type of soft rock to

to the adits Adits & Shafts Durability related design characteristics Carbon steel HDPE (internal) Epoxy coating (external) Traditional steel + steel fibre HDPE

7 SFRC Lining in Middle East Tunnels COWI designed 3 different SSFRC lining tunnels with diameters variable from 4 to 6m (check) in different type of soft rock to soils: STEP project in Abu Dhabi (UAE), Abu Hamour and Doha Metro projects in Doha (Qatar) Structural parts Typical tunnel segments Special tunnel segments close to the adits Adits & Shafts Durability related design characteristics Carbon steel HDPE (internal) Epoxy coating (external) Traditional steel + steel fibre HDPE (internal) Epoxy coating (external) Traditional steel Epoxy coating (internal) Min/nom cover mm N.A. 60/65 (internal & external) 75/85 (internal) 60/70 (external) 7

SSFRC Lining in Middle East Tunnels The fibers: The solution for tunnel segments durability Standard solution for high concentration of chloride and sulphate.

8 SSFRC Lining in Middle East Tunnels The fibers: The solution for tunnel segments durability Standard solution for high concentration of chloride and sulphate. Structural parts Typical tunnel segments Special tunnel segments close to the adits Adits & Shafts Durability related design characteristics Steel fibre HDPE (internal) Epoxy coating (external) Traditional steel + steel fibre HDPE (internal) Epoxy coating (external) Traditional steel Epoxy coating (internal) Min/nom cover mm N.A. 60/65 (internal & external) 75/85 (internal) 60/70 (external) 8

9 Damaged Segments RC segments : fragile material (RC) + high concrete covers (Durability) = Widespread failures of edges/corners/grooves 9

10 Damaged Segments SEVERAL CMS OF CONCRETE ARE 10 UNPROTECTED

11 Damaged Segments Assembling issues: Greater ductility of the material + Greater impact resistance = Improved redistribution of the stresses in case of unforeseen loads 11 less thick cracks

margin of safety THERE IS NO REINFORCEMENT LIMITING THE DIFFUSION

12 Damaged Segments HIGH UNFORENSEEN OVERSTRESS (SEGMENTS MISALIGNMENTS IN THE ORDER OF CMS) RC segments offer a greater margin of safety THERE IS NO REINFORCEMENT LIMITING THE DIFFUSION OF THE CRACKS Less margin of error during the installation of the segments! 12

SFRC is loved by the contractor No need of a

equipment and no need of as high-qualified

13 SFRC is loved by the contractor No need of a dedicated plant for steel cages production Easy addition of the fibers to the concrete aggregates by means of a feeder Very simple equipment and no need of as high-qualified workmanship as opposed to steel cages production 13

contribution is offered by PPF (average dosage 1-1.

14 Fire Protection PPF Fibers Steel fibers contribute to increase the fire protection against spalling, however, the greater contribution is offered by PPF (average dosage kg/mc) PPF affects greatly the workability of the concrete mix 1 kg/m 3 1 slump class down 14

15 Stray Current No Steel Bars No corrosion issues (environment and stray current) No current dispersion system in the segments No need to monitor the corrosion 15

16 Sustainability: Significantly Less Steel Reinforcement SAVING ON THE MATERIAL ( - 60% Steel ) RC segments: kg/mc SFRC segments: kg/mc Example: 1km of metro tunnel with ordinary steel reinforcement tons of steel Economical and eco-friendly choice 16

Demanding Design and Approval Process Some Clients/ Agencies may be reluctant to accept the full SFRC solution. Not fully known general standards. A few projects worldwide.

17 Demanding Design and Approval Process Some Clients/ Agencies may be reluctant to accept the full SFRC solution. Not fully known general standards. A few projects worldwide. Design focused in the segment details (borders, corners, holes) to minimize the tensile stress. Design focused in the detailed assessment of pushing rams phases and tensile stress. 17

18 OPTIMIZATIONS SCFR Lining Design REQUIREMENTS STUDY PHASE PRODUCTION PHASE THEORETICAL STUDY CLIENT TESTING CONTRACTOR SFRC SPECIFICATION SPERIMENTAL STUDY FINE TUNING ORDINARY PRODUCTION DESIGNER 18 NEED TO HAVE SOMEONE WITH A CLEAR PICTURE OF THE REPERCUSSIONS OF ANY CHANGE IN BOTH STUDY AND PRODUCTION PHASE.

FINE TUNING SCFR - Design PRODUCTION ISSUES RELATED TO THE USE OF SF AND PPF WORKABILITY, AD-HOC MIX DESIGN, USE OF ADMIXTURES A FINE TUNING OF THE CONCRETE MIX DESIGN COULD BE REQUIRED IN FUNCTION

19 FINE TUNING SCFR - Design PRODUCTION ISSUES RELATED TO THE USE OF SF AND PPF WORKABILITY, AD-HOC MIX DESIGN, USE OF ADMIXTURES A FINE TUNING OF THE CONCRETE MIX DESIGN COULD BE REQUIRED IN FUNCTION OF THE EQUIPMENT IN USE Cement Water Aggregates Steel Fibers PP Fibers Admixtures CONCRETE MIX DESIGN!!! MOULDS VIBRATION SYSTEM AFFECTS GREATLY THE FINAL RESULTS AND MIX DESIGN COULD BE REQUIRED TO BE OPTIMIZED 19 EQUIPMENT

20 SFRC Design SFRC Design of the details 20

Conclusions 21 TREND : The use of SCFR is the future of most of the TBM tunnels lining. ISSUES : The operators may be skeptical about SCFR. A few projects worldwide.

21 Conclusions 21 TREND : The use of SCFR is the future of most of the TBM tunnels lining. ISSUES : The operators may be skeptical about SCFR. A few projects worldwide. The technology requires very high level of contractor and designer. The project present major risks. SOLUTION : Effective collaboration between involved parts (Client/contractor/designer) High skilled designer and contractor

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