Case Studies: Thessaloniki Metropolitan Railway (Greece)

Objective
Thessaloniki Metro is considered as the most extensive transport project in Northern Greece underway and is expected to be completed in three construction phases. At the moment, Phase 1 and Phase 2 of the project are in progress. Phase 1 involves the construction of the base underground line. The Line consists of two independent single-track tunnels, which form a network with an overall length of 9.6km. Along its length, 13 modern center platform stations will serve the 18 fully automatic driverless metro trains which are expected to carry 18000 passengers per hour in each direction. The 7.7km section constructed by means of two Tunnel Boring Machines has already been completed. The remaining section of the base line will be constructed by applying the Cut and Cover method. Com-pletion of Phase 1 is expected by the end of 2020.

The Challange
An integrated system consisting of HDPE geomembranes (1.5mm and 2.0mm thick) was qualified for waterproofing (i) the bottom and the lateral concrete walls of the stations and (ii) the shell of the tunnels. Needle-punched nonwoven geotextiles weighing 500gr/m2 and 800gr/m2 were specified as cushions for protecting the geomembranes.
At the formation level (under the concrete floor of the stations), a 140gr/m2 needle-punched nonwoven geotextile was specified to separate the existing soil at the bottom of the excavation from the drainage layer consisting of a typical 30cm thick base course gravel. Over the aggregates, the installation of the waterproofing system and the construction of each station was planned to follow.

The Solution
Following the specifications of the design for cushioning materials, Thrace Nonwovens & Geosynthetics provided needle-punched nonwoven geotextiles weighing 500gr/m2 and 800gr/m2 namely P500NW and P800NW, respectively. The geotextiles were used to protect both sides of the geomembranes from damage due to contact with either the coarse particles of the drainage layer or the protrusions on the rough concrete/shotcrete surfaces. A 140gr/m2 needle-punched nonwoven geotextile, under the trade description S12NW, was provided to act as a separator. The specific geotextile had the appropriate hydraulic characteristics to serve efficiently as filter for the aggregate layer, as well.

After works resumed in March of 2016, more than 150.000 sqm of THRACE NG nonwoven geotextiles have been installed all along the base underground line.

Figure 1: View during construction

Figure 2: Geomembrane placement on top of the cushion geotextile

Figure 3: Cushion geotextile installation

Figure 4: Spreading of the aggregates upon the geosynthetic separator

Further information
For more information on Thrace products and systems, visit www.thracegroup.com

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