Abstract: A tunnel excavator includes a pair of cutters arranged side by side at a front portion of a tunnel excavator main body. These cutters rotate in opposite directions for excavating the earth to form excavation and for causing the excavated earth to move toward a center area between the pair of cutters. The tunnel excavator further includes a screw cutter extending horizontally in a width direction of the tunnel excavator behind the pair of cutters at a lower level. The screw cutter has a pair of flights spiraling in opposite directions toward the center from opposite ends of the screw cutter for gathering the excavated earth to the center of the screw cutter. A soil plate generally extends along and behind the screw cutter and pushes the excavated earth as the tunnel excavator advances, but the soil plate has an outlet at a lower center area thereof for allowing the excavated earth to pass therethrough. A conveyor is provided behind the soil plate outlet.

Abstract: The tunnel excavator (1) includes a cutter supporting body (3) provided with cutters (2) for excavating the earth. The tunnel excavator also includes crawlers (13) for moving backwards and forwards, and upper and side bearing frames (15, 16) which move radiantly until they contact an inner surface of the excavation (12). Forwards movement is accomplished by propelling the cutter supporting body (3) with the crawlers (13) while the bearing frames (15, 16) are in contact with the inner surface of the excavation (12). Forwards movement without lateral slippage can be achieved because the cutter supporting body (3) is guided through the excavation (12) by the bearing frames (15, 16). Backwards movement is achieved by radially withdrawing the bearing frames (15, 16) from the inner surface of the excavation (12) and reversing the crawlers (13). Tunneling can therefore be accomplished regardless of the state of the floor.