More than 90% of the 15 km tunnel along the 80 km Gautrain route have already been completed, says Gautrain spokesperson Dr Barbara Jensen.

The underground route stretches from Johannesburg Park station, running underneath the Johannesburg hospital, Parktown Ridge, Rosebank, Sandton and Marlboro, to the point where it surfaces at the Marlboro portal.

Three kilometres of the tunnel, the section between Park and Rosebank stations, have already been excavated, using a German-made specialist tunnel-boring machine (TBM).

The remainder of the tunnels are being completed using traditional drill-and-blast methods, with work continuing at various sites.

Dismantling of the TBM is in progress.

Only the 12-m long outer steel shield at the front end of the machine will remain where it is currently parked inside the tunnel, and this will be covered with a permanent shotcrete lining. The back-up system, comprising 13 gantry trailers, mechanical and electrical components and support equipment, will be recovered and reconditioned for use on other tunnelling projects.

The Gautrain tunnel route will feature several emergency access shafts.

These shafts will provide emergency services personnel access to the tunnels below, should it be necessary. At the bottom of some of these shafts there will be safe havens, where passengers can gather in case of an emergency.

Here is a graphical update of the tunnelling work on the R25-billion project, which will link Tshwane, Johannesburg and the OR Tambo International Airport by 2011.