Main contractor China Civil Engineering Construction Corporation (CCECC) has announced that it has achieved breakthrough on the second bore of the Ganntas Tunnel in Algeria after six years on site.
According to CCECC, the complex marl ground conditions were challenging for the twin bore tunnel scheme and were called “the disaster of geological engineers” by French engineers working on the project.
It is the first long tunnel to be built in Africa with each of the bores measuring 7.3km.
The tunnels were excavated using hydraulic hammer working on eight faces with access from the portals and a shaft near the centre of the tunnel. Temporary support was provided by shortcrete, bolts and steel ribs and followed by a cast insitu concrete lining.
According to consultant to the scheme Systra, extreme squeezing conditions were encountered when the alignment passed through a fault zone in the soft clayey marls and reprofiling of the tunnel was necessary over a 100m section.
Despite the ground conditions, CCECC said that at peak it managed to bore 870m per month.
The tunnel will significantly reduce the travel time between Oran and Algiers.