The use of Needle-punched nonwoven geotextiles in Underground Works

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Summary:

GREECE – Thessaloniki – Thessaloniki Metropolitan Railway (AKTOR S.A)

THRACE Nonwovens & Geosynthetics S.A

A variety of needle-punched nonwoven geotextiles were installed during the construction of the entire Thessaloniki Metropolitan Railway network. Cushion geotextiles were incorporated into the waterproofing system for providing protection to HDPE geomembranes. Geotextile separators were used to ascertain operational integrity of the soils in the bottom of the excavations.

Thessaloniki Metropolitan Railway is the most extensive transport project underway in Northern Greece and is to be completed in three construction phases. Currently, Phase1 and Phase2 are in progress. Phase1 involves the construction of the base underground line, which consists of two independent single-track tunnels forming 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/hour, in each direction. The 7.7km section constructed by means of two TBMs has already been completed. The remaining section of the base line is constructed by applying the Cut & Cover method. Completion of Phase1 is planned within 2020.

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/sqm and 800gr/sqm were specified as cushions for protecting the geomembranes. At the formation level (under the concrete floor of the stations), a 140gr/sqm 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. Over the aggregates, the installation of the waterproofing system and the construction of each station were carried out.

 

Following the specifications, Thrace Nonwovens & Geosynthetics supplied the cushion geotextiles P500NW and P800NW to protect both sides of the geomembranes from being damaged by the contact with either the coarse particles of the drainage layer or the protrusions of the concrete/shotcrete surfaces. For serving as a separator in the excavation, the geotextile S12NW was supplied, as well.

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