Metro officials mull over safer ways to tunnel

The Metro has come up against the biggest stumbling block in the process of its construction. Just a few weeks after Metro works caused a large hole to open up on Doukissis Plakentias Street in Halandri – which injured one person and damaged the tunnel being constructed – the Attiko Metro firm now faces particularly complex and more intricate problems in the district of Peristeri. The management of Attiko Metro has long been troubled by the bad quality of the earth that Attiko Metro’s tunnel-boring machine (TBM) has had to cut through to extend the metro’s Line 2 from Sepolia to Aghios Antonios in Peristeri. Attiko Metro officials briefed Canadian tunnel expert Evert Hook – who is visiting Athens to examine the reasons for the subsidence in Halandri – on the situation in Peristeri. According to Hook, the composition and layering of the earth in the area is not suitable for the use of a TBM – a machine recommended for use in areas with homogenous soil. In Peristeri, the soil is weak in its composition and geologically varied, and so needs special attention. And so Attiko Metro now faces a dilemma. Either it continues tunneling for the remaining 800 meter stretch of the metro extension using the TBM while implementing extra protection measures (such as supportive poles and earth reinforcement), or it can implement the new Austrian (NATM) method, a standard technique of underground digging. Both approaches will involve extra investment. So Attiko Metro is currently assessing the pros and cons of both, comparing relative costs in order to determine the most appropriate solution. The construction of the Aghios Antonios station in Peristeri is due to be completed before the 2004 Olympics and its operation during that period is regarded as essential. In any case, it seems Attiko Metro officials are veering toward the NATM method, which they believe would be a safer and more appropriate way of completing works than if the TBM were to be used. And, after the incident in Halandri, no one wants to take any risks.

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