Continuous tunnel boring machine and method

In a tunneling machine comprising end-to-end front and rear tubular shields, said rear shield including a tail section which extends rearwardly and provides space under cover within which a tunnel lining is constructed, main thrust ram means interconnected between the front and rear shields, for shoving the front shield forwardly relative to the rear shield and for steering said front shield relative to said rear shield;

• auxiliary thrust rams mounted on said rear shield and extendable rearwardly to contact the tunnel lining, the improvement comprising:
• said auxiliary thrust ram means comprising a plurality of groups of thrust rams, with each such group comprising circumferentially adjacent thrust rams in a continuous peripheral zone of the rear shield, extendable rearwardly in unison a distance at least slightly larger than the axial length of a tunnel lining segment;
• said main thrust rams means being extendable rearwadly in unison a distance which is substantially 1/x of the stroke of the auxiliary thrust rams, where x is the number of groups of auxiliary thrust rams;
• and
• said groups of auxiliary thrust rams being progressively offset an amount substantially equal to the stroke of said main thrust ram means,
• whereby one group of the auxiliary thrust rams means can be retracted and tunnel lining installed between them and a previously installed portion of tunnel lining while the other groups of auxiliary thrust rams are extended against previously installed portions of the tunnel lining and the main thrust rams are being used for moving the front shield relative to the rear shield.