Structural design of tunnel lining

tunnel lining may be permanent or temporary based upon their use and requirement. design of lining is done in two parts one is temporary or initial lining design and other is permanent design of the lining. empirical and theoretical methods are major design methods.

1. STRUCTURAL DESIGN OF TUNNEL LINING PRESENTED BY: Mahesh Raj Bhatt M.E. In Structural Engineering Kathmandu University 31th march-2017

2. Content outline: Team work in tunnel design Fundamental approach of design Lining in tunnel Mode of failure in lining Design of lining Initial design Final design Conclusion

3. Team work in tunnel design: Engineering Geologist: geo-exploration Hydraulics engineer: tunnel pressure, profile Structural engineer: lining type and material selection Geotechnical engineer: ground support requirement Civil engineer: construction, location, layout Surveyor: maps, geometric frameworks Environmentalist: Environmental issues Construction engineer: construction issue Other experts: estimation, costing, quality expert etc.

4. Fundamental approach of design: Engineers promise that the structure will neither suffer structurally nor collapse during its projected lifetime. Design must be Safe Stable functional Possible failure modes should be analyzed.

5. Lining in tunneling: Steps in structural design construction Excavation : Blasting / mechanical tools Initial ground support: safety during work Final ground support: structural safety what is tunnel lining ? timber , brick, concrete, or steel supports erected in a tunnel to maintain dimensions and safe working conditions. And finally for permanent safety of the system.

6. Mode of failure in tunnel Can be categorized Failure due to discontinuity: fault, joint, fold due to stratified rocks Rock fail by stress: squeezing, in fault zone, weak and expansive soil in deeper zone. Fail by mineral control Water pressure control: swalling Seismic effects Other permanent soil land displacement Failure in shortcrete Failure in rock bolt and dowel system etc.

7. Fig: tunneling in Rock stratification:

8. Design of lining Types: a) Design of initial support installed after excavation to support the opening safely. b) Design of final lining: to make the structural safety and stability

9. a) Design of initial support: Based upon: how to select material for support empirical method : Terzaghi (1946) Theoritical method / analysis method Fundamental approach : based on potential failure mode Imperical method : (design of steel ribs) -based on the experience - terzagi (1946) gave written rule for selection based on Rock loads and RQD-index of the rock . (RQD=rock quality designation)=degree of joint in rock mass

10. Skinner , Wickman , Tiedeman (1972) Gave Rock structure rating ( RSR ) Rock type Joint Discontinuity Fault Fold Orientation based

11. ii) Theoretical method: It deals with design of rock bolts Dowels Shortcrete Steel ribs design Rock bolts: based on 3-D wedge analysis Shortcrete: to make immediate stiffness to excavated rocks Dowel: to support mass / and reduce deflection

12. Design of steel ribs: Bent I-section or H-section made circular (steel) Ribs are oriented to act as arch action which reduces moment in the section.

13. b) Design of final lining: Common options are: Un reinforced concrete Reinforced concrete Segmental concrete Steel backfill with concrete Concrete pipe with backfill Steel backfill with grout Note: interaction between rock and lining material is important to design the lining in tunneling.

14. Unlined tunnel : water excess to rock Shot- crete : to provide ground support, hydraulics Un reinforced line : to protect rock exposure, smoothen Reinforced line : 1-laye r:temperature stress and shrinkage Multi layer : swelling, squeezing, high stress Steel lining : when internal pressure > external pressure/ ground or ground water

15. Load cases for design:

16. Design requirements: Lining thickness : tmin >300 mm Min cover>100mm Guideline EM-1110-2-2104 for concrete cover concrete mix design : Most cases=M21 (21 mpa ) Thin line =M35 Segmental line=M42 Reinforcement: 0.28% of X-section of line 0.4% for blast type tunneling note: reinforce for crack control due to temperature/pressure etc .

17. Lining for external water pressure: If P external water< P internal water Than take P ex=Pin ( because leakage increases external pressure ) if Tlining < R/10 (R-radius of tunnel)

18. If T lining>R/10

19. Circular tunnel with internal pressure: Concerns are mainly on Rock lining interaction estimation of lining leakage 1) Rock lining interaction - thin shell equation ( radial displacement of lining) - cylinder theory for thick lining

20. To find radial displacement of lining :

21. 2) Lining leakage estimation:

22. Lining for bending and distortion:

23. Note: moment and forces analysis must be done using Finite element analysis tools

24. Design of steel liners: Amstutz (1970) Jacobson(1974) Vaughan (1956) Moore (1960 ) computer solution: To find the critical buckling pressure .

25. Linear ring lining design: basic approach A liner ring is statically indeterminate. A one pass lining is designed for transport and erection loads, loads during grouting, and ground loads For a circular ring of constant cross section symmetrically loaded the thrust at the crown C is

26. Note: in ring segmental design all the analysis procedure is same as like as parabolic/circular arch. Based upon the fined analysis result rebar must be designed . (horizontal thrust/ shear / and moment are governing parameters for the lining rebar design)

27. CONCLUSIONS : Lining design should be safe , stable and functional Lining type depend upon the property of the interior rock or soil. To save the rock portion to be exposure , lining is done. To give additional support to rock mass lining is needed. There are various methods for lining design these may be not structural sometime these may be only based upon the constructional approach .

28. Thank you!! THANK YOU!! Tunnel spillway in Kanogawa dam Japan

29. References : Engineering and design tunnel and shaft in rock, CECW-EG Engineer Manual1110-2-2901 Department of the Army U.S. Army Corps of Engineers Washington, DC 20314-1000 TUNNEL ENGINEERING, 20 Lars Christian F. Ingerslev , Arthur G. Bendelius Parsons Brinckerhoff New York, New York PRACTICAL TUNNEL, CONSTRUCTION Gary B. Hemphill PhD, PE, JOHN WILEY & SONS, INC.