TWO STAGE TYPE SHIELDING DEVICE

PURPOSE: To enhance operating efficiency by providing a large-bore shield device at the center of a front drilled part, which device consists of a center hole parallel to the axis of a tunnel and a reaction wall for an inner small-bore shield, and providing a small-bore shield device within the center hole. CONSTITUTION: A reaction wall 41 is provided inside a large-bore shield device 1 and a drill bit is positioned on the disk of a cutter head 2. A center hole 26 equivalent to a small-bore shield device 5 is bored in a center part parallel to a tunnel axis. A rotating motor 3 for rotating the cutter head 2 is fixed to a wall body 31. The reaction wall 41 is located at the rear for reaction during propulsion of the small-bore shield device 5, and an injector 52 for injecting chemicals into ambient ground is provided inside the small-bore shield device 5. Therefore, the injection of chemicals into a forward wide range is made possible and a wide range of the ground can be drilled efficiently.