Abstract: The invention is directed to a tunnel-driving machine designed to bore a tunnel and having, in addition to a large outer cutter wheel, a smaller central cutter wheel which is mounted near the hub of the outer cutter wheel and which enables the formation of soil plugs and dead cores to be avoided along the longitudinal axis of the cutting wheel, thus reducing the resistance of the machine to forward motion.

Abstract: The tunnelling machine for driving inaccessible tunnels by pressing forward by means of tubes can be moved out again through the tunnel driven by it. For this purpose, an annular outer area (2b) is provided on the extracting tool (2), and one double casing (4b, 6b) each is provided around the control head (4) and the machine tube (6). The outer area (2b) of the extracting tool is connected to its inner area (2a) and the control-head double casing (4b) is connected to the control-head housing (4a) by connecting elements (24, 26). Specifically releasable restraining devices (28) hold the machine-tube double casing (6b) on the machine-tube housing (6a). After the final depth is reached, the control head (4) can be moved back by means of the control devices (40) to such an extent towards the machine tube (6) that the connecting elements (24, 26) are broken.