A COMPLICATED TUNNEL DRIVING METHOD

Tunnel driving with such a shield consists of excavating in the centre at the front of the tube, then pressing the whole shield forward one step by means of the jacks located on the periphery of the intermediate part. The jacks are here braced against the previously mounted lining which practically always consists of cast iron or concrete sections, assembled in rings in the tail part. Each move forward is then equivalent to the length of one such lining ring.