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23 Oct. 2009

Site reports

#49

As a consequence, the TBM was obliged to stand still for an extended

period while personnel undertook an extensive maintenance campaign

under hyperbaric conditions to remove iron and substitute the damaged

tools. In one week, a record eight hyperbaric interventions were carried

out under a pressure of 1.7 bar.

The north TBM faced the further challenge of passing under the 15th

century Alkazar mosque. The religious building showed a top level risk

of falling equal to 3 and an extremely frail structure, as proved by

several extended fractures on the dome and on walls. This was due to

the fact that the mosque had been enlarged and recast several times

and suffered earthquake damage. A further critical event then occurred:

while building up the diaphragm walls of the station next to the mosque,

the variation of the hydro geological balance caused the structure a

differential crush of 55 mm, concentrated at the angle under which the

TBM passed. The TBM successfully passed under the Alkazar mosque

in late August 2009.

On the whole, excavation proceeded in an extremely controlled and

optimal way thanks to strict application of excavation and control

procedures, constant parameter analysis and the organisation of

periodical meetings with operators.

The €958 million contract – awarded by Attiko Metro in 2007 to a

consortium of Aegek, Impregilo, Ansaldo Trasporti, Ansaldo Breda and

SELI – includes the design, construction and commissioning of a 7.7 km

twin tunnel, 13 new stations, an operation control centre, connection

works of the line with the rolling stock depot, an administration building

and the rolling stock material. SELI is in charge of boring the tunnels,

utilising two EPB TBMs driving from two opposite portals. The final

tunnels will have an internal diameter of 5.30 m and an external

diameter of 5.90 m and will be lined with 30 cm thick precast concrete

segments. Geology along the alignment is comprised of stiff clay, silty

clay, gravels and clay.

The TBMs are equipped with special safety systems and AFS for the

automatic injection of bentonite to the face in the event of a pressure

Greece

TBMs successfully face several challenges at Thessaloniki metro

The two Herrenknecht EPB TBMs involved in the Thessaloniki metro

construction entered into full production in July 2009. Excavation by

the SELI-Aegek joint venture is now proceeding regularly. After

crossing four metro stations and passing under a 600-year old

mosque with top level risk of caving in, the two EPB TBMs are now

advancing regularly with a daily output of 18.75 m/day and 16.05

m/day, respectively. Since start of excavation, the average output of

the south and north machines has been 12.47 m/day and 14.17

m/day, respectively.

The south TBM output has increased from 6.7 m/day in April 2009 to

18.75 m/day in August 2009. A maximum output of 27 m/day was

achieved on 28 August 2009.

The north TBM output has increased as well, from 5.35 m/day in April

2009 up to 16 m/day in August 2009. A maximum advance of 22.46

m/day was reached on 5 August 2009.

In early 2009, excavation of the first stretch proved to be complex and

was slowed down by several challenges. Several critical situations

complicated work even more: crossing four stations, the presence of

historical buildings and a shallow geology of sand, clay and sandy

clay. Primary grouting was carried out using the bi-component

technique.

The south TBM passed through the first four metro stations where

only diaphragm walls were completed. The station body will be

excavated at a later stage. SELI-Aegek personnel, however,

discovered unexpectedly that diaphragm reinforcement was made of

iron, rather than fibre glass, as previously believed, in two walls of the

first two stations. The second, north TBM found steel reinforcement in

one diaphragm wall of the same station.

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23 Oct. 2009

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#49

hour and reaches mechanical resistances varying from 0.05 to 0.1

N/mm². The resistance to compression depends on cement dosage

and the silicate used. The injection pressure of the backfilling

grouting begins working on the outer surface of the lining,

immediately after the TBM tail shield has passed.

Distribution of grout pressure uniforms immediately after injection,

because the mixture is still in a liquid/plastic status. When the grout

hardens, the surrounding pressure changes in function of the grout

mix compression, the lining deformation and the load of the

surrounding ground.

The ground conditioning agents supplied by InnoTek were added

and mixed with the muck in the TBM excavation chamber. These

agents contribute to form, when mixed with the muck, an

impermeable thick past that is necessary for a proper EPB

operation. These products were sprayed directly to the tunnel face

through the cutterhead as well injected in the excavation chamber.

The same agents also contribute to reduce the energy consumption

and the wear of the cutterhead as well of the screw conveyor.

INNtens TK 57 is a high-performance liquid foaming agent based on

biodegradable anionic surfactants, which can be used both in fresh

and salt water. INNtens TK 57 is biodegradable, non toxic and easy

to use.

INNtens TK 70 is a liquid foaming agent based on a high-efficiency

natural polymer. The foam generated has a high mechanical

resistance and is an excellent lubricant. INNtens TK 70 is quickly

soluble in water, biodegradable and non toxic.

decrease.

Works started in early 2009 and will be completed in 2012. When

operational in 2013, the line will offer capacity for 18,000 passengers

per hour for every track and a train frequency of 90 seconds.

InnoTek products for Thessaloniki metro construction

The successful application of InnoTek products in the Thessaloniki

metro construction project has made excavation easier and facilitated

work progress. These products make it easier to confront geologically

critical situations during excavation and guarantee the stability of the

excavation face. Innotek supplied its special TBM cutting tools made

of tungsten carbide steel extremely resistant to wear (ex. rippers,

cutter bits and scrapers), the EPB ground conditioning agents (i.e.

INNtens TK 57 and INNtens TK 70) and two bi-component grout

plants, for the backfilling of the segmental lining, expressively

designed and manufactured for the Thessaloniki project needs.

InnoTek supplied two backfilling grout injection plants. The plants

themselves are custom-made products that InnoTek designed and

built, based on the real working needs of the Thessaloniki project.

The backfilling grout injection plants enable bi-component, a special

cement compound, to be dosed, mixed and pumped into the annulus

gap behind the segments, through the tail shield of the TBM. The gap

is filled simultaneously with TBM advancement, thanks to injection

pipes positioned in the TBM tail shield.

This system utilises a liquid component “A” (cement, bentonite, water

and setting retarder) and a liquid component “B” (sodium silicate).

When combined, the two components in few seconds react and

change status from liquid to plastic. The plastic status is maintained

for approx. 30 minutes. The compound then hardens in approx. one

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