Excavation of Tunnels

EXCAVATION OF

Author: Partha Das sharma, (B.Tech – Hons., in Mining Engineering)

E.mail: [email protected], Website: http://miningandblasting.wordpress.com/

TERMINOLOGY for UNDERGROUND STRUCTURES

n Aditn Tunneln Subwayn Shaft

Chamber

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n Chambern Portaln Pilot aditn Centren Facen Wall ~ siten Floorn Roof

n Overbreakn Excavated profilen Natural archlingn Loadn Supportn Failuren Gentle failuren Rock burst


n Rock burstn Squeezing groundn Swelling groundn Clay-filled jointn Long term stabilityn Ground treatmentn Support before excavation

n Jet grouted roof covern Shotcrete initial liningn Jet grouted floor covern Top headingn Invert


Invertn Benchn Final concrete liningn SHIELD tunnelling methodn CUT & COVER tunnelling methodn TBM (Full face ~ Total Boring Machine)

TERMINOLOGY for EXCAVATIONS of ROCKS & SOILS

n DRILLINGn Hardnessn Toughnessn Abrasivenessn Structure


n Structuren Drilkling fluids

n AUGERINGn MACHINE BORING

n Total Boring Machine (TBM)n Full face excavation

n BLASTING

n SCRAPINGn RIPPINGn DIGGINGn GROUND WATER

n Control of groundwater


n Control of groundwatern Groundwater flown Rate of flown Volume of flown Boundaries

TUNNEL DESCRIPTION

1. Made into natural material (rocks)2. Empty inside3. Carry the loads itself

Both ends are open to atmosphere


4. Both ends are open to atmosphere5. Generally horizontal6. Thick walled structure looks like cylinder


1- Key stone

2- Arch

3- Wall

4- Floor

5- Bench

6- Bench line or plane

7- Top heading

8- Invert

Tunnel Section for Swelling Ground


1- Digging section

2- Support

3- Swelling section

4- Pressurized area

5- Flow direction of water

SURFACE EXCAVATIONS

n Deformation & failure


UNDERGROUND EXCAVATIONS

n In Rockn In Sediment

n Stability & Archingn Water

q Dry tunnel...............above water table


q Dry tunnel...............above water tableq Wet tunnel..............below water table

n Gasesq Carbon dioxide (CO2)q Carbon monoxide (CO)q Methane (CH4)q Hydrogen sulphide (H2S)q Other gases

n Gas burstsn Rock fallsn Rock burstsn Squeezing groundTemperature


n Temperaturen Subsidence

EXPLORATION & INVESTIGATIONS RELATED of SLOPE STABILITY

n Geomorphologic maping and preparation of longitudinal & cross sections

n Geological maping & surveyings (aerial photographs)


photographs)n Geophysical surveyingsn Underground explorations, boreholesn Ground water surveyingsn Laboratory testsn Model studies

SURFACE EXCAVATIONS

n Permanentn Short term excavations


SUBSURFACE EXCAVATIONS

1. GEOLOGYa. Soil profile or hard rock geologyb. Structurec. Ground water (hydrogeology)


c. Ground water (hydrogeology)d. Stability

2. INVESTIGATIONSa. Mapping (Topographic, geologic, etc...)b. Geophysical surveying (especially seismic

velocity of rocks)


velocity of rocks)c. Trial pits & boreholesd. General and local stability analysise. Decide to excavation method

UNDERGROUND EXCAVATIONS

n Adit, shaft, incline, large chambern Tunneln Subway ~ metroUnderpass


n Underpassn Sheltern Power housen Ware house, store, mining ...etc

GASES (can be lethal or burst)

n Carbon monoxide (CO) 0.97 of airn Carbon dioxide (CO2) 1.53 of airn Methane (CH4) 0.55 of air

(Highly explosive with air) marsh gas


(Highly explosive with air) marsh gas

n Hydrogene sulphide (H2S) 1.19 of air (Highly toxic and explosive)

n Sulphur dioxide (SO2)

n ROCK FALL

n SQUEEZING GROUND (sand, silt, shale, clay)


n ROCK BURST

n BULKING (Increase in volume, 10-40%)

FACTORS EFFECTING EXCAVATION of ROCKS

n Mineralogical composition of rocksn Texture & fabricn Petrographic featuresn Structure


n Structuren Rock massn Strike & dip of beds in relation to face of excavation

n Intensity of tectonic disturbancesn Degreee of weathering

RESISTANCE of ROCKS to EXCAVATION

n Loose soilsn Soil easy to spade n Soil easy to dign Crumbling weak rocks Rocks easy to blast


n Rocks easy to blastn Rocks difficult to blastn Rocks very difficult to blast

TUNNELLING METHODS

SHIELD TUNNELLING METHOD

n This method involves the use of shield machine to drive the tunnels below the ground.

n 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


excavation and construction of the tunnels using precast concrete lining segments of about 1.2 meter width.

n 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.

CUT and COVER TUNNELLING METHOD

n 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.

n Step one :Construction of diaphragm walls, pin piles, and decking.


and decking.n Step two :Excavation within the diaphragm walls, installing struts as work progresses.

n Step three :Construction of permanent floor slabs and walls.

n Step four : Fitting out the internal structures, backfilling, and reinstating the surface structures.

TBM (Tunnel Boring Machine)

1. Mechanical-support TBM 2. Compressed-air TBM3. Slurry shield TBM

Earth pressure balance machine


4. Earth pressure balance machine5. Mixed-face shield TBM

1- Mechanical Support TBM

n 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


ahead of the cutterhead against the surrounding ground.

2- Compressed-Air TBM

n 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.


air in the cutter chamber.

3- Slurry Shield TBM

n A slurry shield TBM has a full-face cutterhead. Confinement is achieved by pressurizing boring fluid inside the cutterhead chamber.


chamber.

4- Earth Pressure Balance Machine

n An earth pressure balance machine has a full-face cutterhead. Confinement is achieved by pressurizing the excavated material in the cutterhead chamber.


cutterhead chamber.

5- Mix-Face Shield TBM

n Mix-face shield TBMs have full-face cutterheads and can work inclosed or open mode and with different confinement techniques.


techniques.

EFFECT of GEOLOGICAL STRUCTURES to TUNNEL EXCAVATION

n Effect of soil layers: horizontal, vertical and inclined layers have different kinds of loading conditions for tunnels.


n 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

n 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.


n 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 vertical Fold axis and the tunnel direction is parallel

CLASSIFICATION of ROCKS for TUNNELING PURPOSES

n Classification of rocks for engineering purposes is needed in analyzing the project costs and to obtain an economic and reliable solution.


solution.

n 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.


Rock classification and determination of unsupported span

ONE of the LONGEST IRRIGATION TUNNELS in the WORLD


Consist of two concrete lined tunnels each of which is 7.62 m in diameter and

26.4 km in length discharging water from


26.4 km in length discharging water from the reservoir of Atatürk Dam.

Excavation of Tunnels

Design

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