Process for making a tunnel and advancing a tunneling read with a wall-supporting shield

A method of forming a tunnel, comprising the steps of:

• (a) advancing a tunnel excavator through a subterranean structure to form a tunnel-shaped excavation therein having a chamber under atmospheric pressure and an exposed excavated wall;
• (b) disposing a tunnel lining in said excavation with all-around spacing from said wall, said tunnel excavator having a tail shield trailing said excavator, lying along said wall and spaced from and surrounding said lining;
• (c) pumping concrete into an annular space defined between said lining and said wall at an elevated pressure;
• (d) confining said space in a direction of advance of said excavator by providing a gap-sealing ring between said tail shield and said tunnel lining;
• (e) supporting said ring with fluid pressure to resist advance of the ring in said direction;
• (f) forcing said ring in said direction with the pressure of the concrete pumped into said space;
• (g) providing a gap between said ring and at least one of said tail shield and said lining;
• and
• (h) sealing said gap by:
• (h.sub.1) incorporating in said concrete a coarse-grained aggregate of a particle size of at least 4 mm and such that said coarse-grained aggregate forms a layer upstream of said gap in a flow direction through said gap,
• (h.sub.2) incorporating the concrete pumped into said space a fine-grained aggregate of a particle size comprising sand or fibers and such that said fine-grained aggregate is trapped in said layer, and
• (h.sub.3) forcing the concrete through said gap so that said layer is formed, traps said fine-grained aggregate and the trapped five-grained aggregate in said layer seals said gap.