The tunnelling for the The tunnelling for the “Metro do Porto“Metro do Porto””

By Alex Wilson & Frances Coker By Alex Wilson & Frances Coker SinghatehSinghateh

Where is Porto?Where is Porto?

North-west coast of Portugal, North-west coast of Portugal, on the mouth of the river on the mouth of the river

DouroDouro

The The metro metro lineslines

Metro FormatMetro Format Comprises 70km of light railway, of which roughly 6.1km Comprises 70km of light railway, of which roughly 6.1km

is in bored tunnel.is in bored tunnel. 12 stations are located underground and were excavated 12 stations are located underground and were excavated

for using the NATM tunnelling system.for using the NATM tunnelling system. Original Budget was 750 million Euros (55million euros Original Budget was 750 million Euros (55million euros

allocated to tunnelling)allocated to tunnelling) Tunnelling started in June 2000 and finished 42 months Tunnelling started in June 2000 and finished 42 months

later.later.

Tunnel – standard underground line

Surface –urban areas with crossroads and traffic lights

Surface – segregated channel with level crossings

PMO GUIFÕES

Airport

Pedras Rubras

Póvoa do Varzim

Trofa

Hosp. São João

Campanhã

Sr. Matosinhos

ISMAI

Fonte de Cuco

Sra. da Hora

Trindade

Casa da Música

Sto Ovideo

Estádio do

Dragão

Major constraint was in the CBDMajor constraint was in the CBD

Porto is Porto is built on built on a a relatively relatively high high gradient gradient river river valleyvalley..

Porto’s GeologyPorto’s Geology Porto is built on a highly variable granite Porto is built on a highly variable granite

Batholith.Batholith. Medium grained 2 mica (igneous rock) granite, Medium grained 2 mica (igneous rock) granite,

which has undergone deep weathering due to which has undergone deep weathering due to the help of tectonic movements, such that the help of tectonic movements, such that decomposed granite are felt next to fresh granite decomposed granite are felt next to fresh granite at various depths and locations.at various depths and locations.

Tunnels pass through ~ 6 grades of weathering Tunnels pass through ~ 6 grades of weathering (W1-W6) and alteration ranging from fresh (W1-W6) and alteration ranging from fresh granite to cohisionless granular soil.granite to cohisionless granular soil.

High water levels , man made ‘minas’ and deep High water levels , man made ‘minas’ and deep wells increased the challenge ahead.wells increased the challenge ahead.

MAN MADE WATER MINESMAN MADE WATER MINES

A typical distribution of weathered granite taken found at the

face of the EPB driven Tunnel.

The different degrees of weathering of the granite taken from a borehole. The

weathered granite on the left side is at a depth of 24m under the sound granite of

the right.

TunnelingTunneling 3 tunnels were to be 3 tunnels were to be

excavated by a TBM excavated by a TBM EPBM boring at up to three EPBM boring at up to three bar pressure .bar pressure .

They were lined with pre-They were lined with pre-cast concrete segments of cast concrete segments of 7-9 m internal diameter7-9 m internal diameter

The machine had a The machine had a nominal face opening of nominal face opening of 20% to allow excavated 20% to allow excavated material to flow through the material to flow through the machine face.machine face.

A continuous conveyor belt A continuous conveyor belt was used to remove the was used to remove the soil before trucks took it soil before trucks took it away.away.

COLLAPSE OF TUNNELCOLLAPSE OF TUNNEL

No sooner had the boring started work on the No sooner had the boring started work on the tunnel, it was stopped as two houses collapsed tunnel, it was stopped as two houses collapsed resulting in the death of one.resulting in the death of one.

This was the third and largest collapse till the This was the third and largest collapse till the surface and it left a 250m³of hole. surface and it left a 250m³of hole.

This happened due to the over excavation and This happened due to the over excavation and face collapse in the extremely heterogeneous face collapse in the extremely heterogeneous geology. geology.

THE COLLAPSE HOUSESTHE COLLAPSE HOUSES

First ActionFirst Action

A commission of inquiries was set up by A commission of inquiries was set up by the government.the government.

16 recommendations were concluded as a 16 recommendations were concluded as a specification guide. specification guide.

The Engineer, Construction manager and The Engineer, Construction manager and the contractor were forced re-think their the contractor were forced re-think their roles.roles.

First Action (cont.d)First Action (cont.d) It concluded that the accident could have It concluded that the accident could have

been avoided. been avoided. Reinforcing team with trained geotechnical Reinforcing team with trained geotechnical

engineers.engineers. Advance knowledge of area to be drilled Advance knowledge of area to be drilled

before the boring is used.before the boring is used. Investigation of the ground structure Investigation of the ground structure

resulted in an additional machine, in resulted in an additional machine, in preparation for advance tunnelling. preparation for advance tunnelling.

SolutionsSolutions Panel of experts after reviewing came up Panel of experts after reviewing came up

with two proposals about the EPBMswith two proposals about the EPBMs

- The use of an automatic bentonite - The use of an automatic bentonite injection system.injection system.

- An additional double piston pump. - An additional double piston pump.

Herrenknecht EPB TBM and Pressure Mechanism

CONTRACTOR’S MODIFICATIONCONTRACTOR’S MODIFICATION

10 independent foam generators.10 independent foam generators. New rotary fluid joint.New rotary fluid joint. New twin belt weighing system.New twin belt weighing system. An early alert system in place when an An early alert system in place when an

operator reaches any critical level.operator reaches any critical level.

CONCLUSIONCONCLUSION

Despite the safety precautions in place the Despite the safety precautions in place the use of TBM was recommended. use of TBM was recommended.

Daily meetings held with management Daily meetings held with management team to share information and any team to share information and any problem that may arise.problem that may arise.

Could have tried other tunneling methodsCould have tried other tunneling methods

(i.e.Cut-and-cover method, Drill and blast, Immersed (i.e.Cut-and-cover method, Drill and blast, Immersed tube method, Lunardi Method, Slurry-shield machine, tube method, Lunardi Method, Slurry-shield machine, Wall-cover construction method )Wall-cover construction method )

ReferencesReferences http://http://www.rocscience.comwww.rocscience.com/ hoek/references/H2004e.pdf/ hoek/references/H2004e.pdf

http://http://users.ntua.gr/marinusers.ntua.gr/marin os/downloads/conference_inaveiro.pdfos/downloads/conference_inaveiro.pdf

http://http://www.rocscience.comwww.rocscience.com/ hoek/references/H2005c.pdf/ hoek/references/H2005c.pdf

http://www.iom3.org/materi alsworld/feature-pdfs/jul06/Porto%20pressure.pdfhttp://www.iom3.org/materi alsworld/feature-pdfs/jul06/Porto%20pressure.pdf

http://www.ita-aites.org/chttp://www.ita-aites.org/c ms/ ms/fileadmin/filemounts/gefileadmin/filemounts/ge neral/pdf/ItaAssociation/ProductAndPublication/Trainneral/pdf/ItaAssociation/ProductAndPublication/Train ing/Seminars/2006-lisbon/Cunha_abstract.pdfing/Seminars/2006-lisbon/Cunha_abstract.pdf

http://http://www.efrtc.org/htdocwww.efrtc.org/htdoc s/newsite/events/Genmeet_2 s/newsite/events/Genmeet_2 005_Marques.ppt#685,28,II005_Marques.ppt#685,28,II. Engineering . Engineering