Bridge used to leverage giant TBM

Dismantling and removal of the of the 13.2m diameter TBM for Sochi Olympics motorway tunnels began late last month. The 1,600t Herrenknecht TBM was used to cut the northern section of motorway Tunnel System Number Three , part of the combined road rail route carrying traffic from Adler in Sochi, Russia to the nearby mountain resort of Alpika-Service. The machine took two years to excavate the 3,117m long tunnel, breaking through in March.

Before the tunneling operations completed, Russia-based contractor SK Most prepared the ground for the removal of the huge machine. For the smooth removal of the TBM a concrete bed was needed at the northern tunnel portal. However, the northern portal was congested by the ongoing construction of a cable-stayed bridge within the narrow valley of the Mzymta River, leaving no room to place the concrete. The bridge forms the next northerly section of the motorway.

Engineers developed a solution whereby the bridge frame is used to support the dismantling and removal of the TBM. "The concrete bed for disassembly of the tunneling machine rests upon the supports of the viaduct section of the cable-stayed bridge," explained Dmitry Korolev, production manager of the Sochi branch of OJSC STROY-TREST, a subsidiary of SK Most. “This solution had to be used because of a number of restrictions: first, the site is within narrow constraints of the mountains and, second, it is confined to the unstable bank of the Mzymta River."

The contractor said it will take seamless cooperation between the tunnelling and bridge building companies to dismantle TBM on the site of an under-construction bridge. The operations are scheduled to be completed within two months. Tunnel System Number Three contained the most tunnel work on the route and the most challenging geology which included 27 fracture zones.