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Excavation of Tunnels
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Excavation of Tunnels


excavation of tunnels

excavation of tunnels

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  • 1. EXCAVATION OF Author: Partha Das sharma, (B.Tech – Hons., in Mining Engineering) E.mail:, Website:
  • 2. TERMINOLOGY for UNDERGROUND STRUCTURES Adit Tunnel Subway Shaft Chamber Portal Pilot adit Centre Face Wall ~ site Floor Roof 2
  • 3. Overbreak Excavated profile Natural archling Load Support Failure Gentle failure Rock burst Squeezing ground Swelling ground Clay-filled joint Long term stability Ground treatment Support before excavation 3
  • 4. Jet grouted roof cover Shotcrete initial lining Jet grouted floor cover Top heading Invert Bench Final concrete lining SHIELD tunnelling method CUT & COVER tunnelling method TBM (Full face ~ Total Boring Machine) 4
  • 5. TERMINOLOGY for EXCAVATIONS of ROCKS & SOILS DRILLING Hardness Toughness Abrasiveness Structure Drilkling fluids AUGERING MACHINE BORING Total Boring Machine (TBM) Full face excavation BLASTING 5
  • 6. SCRAPING RIPPING DIGGING GROUND WATER Control of groundwater Groundwater flow Rate of flow Volume of flow Boundaries 6
  • 7. TUNNEL DESCRIPTION 1. Made into natural material (rocks) 2. Empty inside 3. Carry the loads itself 4. Both ends are open to atmosphere 5. Generally horizontal 6. Thick walled structure looks like cylinder 7
  • 8. 8
  • 9. 1- Key stone 2- Arch 3- Wall 4- Floor 5- Bench 6- Bench line or plane 7- Top heading 8- Invert 9
  • 10. Tunnel Section for Swelling Ground 1- Digging section 2- Support 3- Swelling section 4- Pressurized area 5- Flow direction of water 10
  • 11. SURFACE EXCAVATIONS Deformation & failure 11
  • 12. UNDERGROUND EXCAVATIONS In Rock In Sediment Stability & Arching Water Dry tunnel...............above water table Wet tunnel..............below water table Gases Carbon dioxide (CO2) Carbon monoxide (CO) Methane (CH4) Hydrogen sulphide (H2S) Other gases 12
  • 13. Gas bursts Rock falls Rock bursts Squeezing ground Temperature Subsidence 13
  • 14. EXPLORATION & INVESTIGATIONS RELATED of SLOPE STABILITY Geomorphologic maping and preparation of longitudinal & cross sections Geological maping & surveyings (aerial photographs) Geophysical surveyings Underground explorations, boreholes Ground water surveyings Laboratory tests Model studies 14
  • 15. SURFACE EXCAVATIONS Permanent Short term excavations 15
  • 16. SUBSURFACE EXCAVATIONS 1. GEOLOGY a. Soil profile or hard rock geology b. Structure c. Ground water (hydrogeology) d. Stability 16
  • 17. 2. INVESTIGATIONS a. Mapping (Topographic, geologic, etc...) b. Geophysical surveying (especially seismic velocity of rocks) c. Trial pits & boreholes d. General and local stability analysis e. Decide to excavation method 17
  • 18. 18
  • 19. UNDERGROUND EXCAVATIONS Adit, shaft, incline, large chamber Tunnel Subway ~ metro Underpass Shelter Power house Ware house, store, mining ...etc 19
  • 20. GASES (can be lethal or burst) Carbon monoxide (CO) 0.97 of air Carbon dioxide (CO2) 1.53 of air Methane (CH4) 0.55 of air (Highly explosive with air) marsh gas Hydrogene sulphide (H2S) 1.19 of air (Highly toxic and explosive) Sulphur dioxide (SO2) 20
  • 21. ROCK FALL SQUEEZING GROUND (sand, silt, shale, clay) ROCK BURST BULKING (Increase in volume, 10-40%) 21
  • 22. FACTORS EFFECTING EXCAVATION of ROCKS Mineralogical composition of rocks Texture & fabric Petrographic features Structure Rock mass Strike & dip of beds in relation to face of excavation Intensity of tectonic disturbances Degreee of weathering 22
  • 23. RESISTANCE of ROCKS to EXCAVATION Loose soils Soil easy to spade Soil easy to dig Crumbling weak rocks Rocks easy to blast Rocks difficult to blast Rocks very difficult to blast 23
  • 25. SHIELD TUNNELLING METHOD This method involves the use of shield machine to drive the tunnels below the ground. After completion of a work shaft, the shield machine is lowered into the shaft and assembled there before excavation and construction of the tunnels using precast concrete lining segments of about 1.2 meter width. This construction method causes minimal disruption to traffic and the environment because all the work takes place below ground and the ground level environment is unaffected. 25
  • 26. 26
  • 27. CUT and COVER TUNNELLING METHOD This construction method, whereby the site is fully excavated, the structure built and then covered over, uses diaphragm walls as temporary retaining walls within the site area. Step one :Construction of diaphragm walls, pin piles, and decking. Step two :Excavation within the diaphragm walls, installing struts as work progresses. Step three :Construction of permanent floor slabs and walls. Step four : Fitting out the internal structures, backfilling, and reinstating the surface structures. 27
  • 28. 28
  • 29. TBM (Tunnel Boring Machine) 1. Mechanical-support TBM 2. Compressed-air TBM 3. Slurry shield TBM 4. Earth pressure balance machine 5. Mixed-face shield TBM 29
  • 30. 1- Mechanical Support TBM A mechanical-support TBM has a full-face cutterhead which provides face support by constantly pushing the excavated material ahead of the cutterhead against the surrounding ground. 30
  • 31. 2- Compressed-Air TBM A compressed-air TBM can have either a full- face cutterhead or excavating arms. Confinement is achieved by pressurizing the air in the cutter chamber. 31
  • 32. 3- Slurry Shield TBM A slurry shield TBM has a full-face cutterhead. Confinement is achieved by pressurizing boring fluid inside the cutterhead chamber. 32
  • 33. 4- Earth Pressure Balance Machine An earth pressure balance machine has a full-face cutterhead. Confinement is achieved by pressurizing the excavated material in the cutterhead chamber. 33
  • 34. 5- Mix-Face Shield TBM Mix-face shield TBMs have full-face cutterheads and can work inclosed or open mode and with different confinement techniques. 34
  • 35. EFFECT of GEOLOGICAL STRUCTURES to TUNNEL EXCAVATION Effect of soil layers: horizontal, vertical and inclined layers have different kinds of loading conditions for tunnels. 35
  • 36. Effect of faults: the relation between the fault slope direction and the tunnel direction, width of the fault zone, type and thickness of the fill material and the hydrostatic pressures in both sides of the fault are some problems in the tunnelling. Relation between the fault zone and the tunnel 36
  • 37. Tunnel excavations in the slopes: the discontinuities (layers, fissures) inclined inside or outside of the slope are very important regarding the stress and strength of the tunnel. 37
  • 38. Effect of the folds: While tunnel is excavated in an area that contains folded rocks, different stresses and conditions may occur depending on the fold type. Fold axis and the tunnel direction is parallel Fold axis and the tunnel direction is vertical 38
  • 40. Classification of rocks for engineering purposes is needed in analyzing the project costs and to obtain an economic and reliable solution. The classification of the rocks, that the tunnel will be constructed in, is first done by Terzaghi. But, it is too general and gives qualitative results. 40
  • 41. Rock classification and determination of unsupported span 41
  • 43. Consist of two concrete lined tunnels each of which is 7.62 m in diameter and 26.4 km in length discharging water from the reservoir of Atatürk Dam. 43
  • 44. 44