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    24 January, 2021 / 0 Comments THE ABDALAJIS TUNNEL (Malaga- Spain)

    The new high speed railway lines under construction in Europe foreseen the execution of very long large diameter tunnels under the most variable rock conditions. Standard Single Shield and Double Shield TBM are not always the right answer for the excavation of these tunnels, especially when adverse rock conditions are expected with rapid squeezing ground and/or face collapses. The Abdalajis tunnel is a twin 7,1 km long 10 m diameter railway tunnel, part of the new high speed line connecting the city of Malaga with Cordoba, in the south of Spain. The present article deals with the TBM excavation of the Abdalajis Tunnel East, where SELI is actively involved in the construction as partner of the Dragados-Tecsa-Seli-Jager Joint Venture. (The Abdalajis Tunnel West, that runs parallel to the East one, is executed by the Spanish Company SACIR with the same technologies) A new type of TBM, named Double Shield Universal (DSU TBM) and manufactured by Mitsubishi, has been developed for the execution of the tunnel. The DSU TBM has been designed as an evolution of the Double Shield TBM to cope with rapid squeezing ground, being able to treat and to stabilise the rock ahead of the tunnel face through the combination of piles and special grouting. The ground conditions encountered in the first section of the tunnel excavated until September 2004 are below the today technical limits for TBM application especially for this range of tunnel diameters. The argillite rock formations crossed in long sections of the tunnel are completely altered and faulted, with rapid convergence of the tunnel walls associated to large instabilities of the tunnel face (ravelling ground) and to methane gas inflows with pressures up to 11,5 bars. The article, moreover, deals with the performances of the DSU TBM in extreme ground conditions and evaluates the possible improvements to this type of TBM to further extend its capacity to the most critical situations.

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