SHIELD EXCAVATOR

PURPOSE:To excavate a tunnel which is so formed as to have an almost flat lower portion by deciding most part of a tunnel opening using a first cutter face, and surely drilling a front working face with a second cutter face. CONSTITUTION:A first cutter face 10 is installed the outer form of which when seen from the front side is like a fan including a circular portion extending along the upper portion of a tunnel and which has drilling blades 11 and earth inlets 12 radially disposed therein and which oscillates about the center O of curvature of the circular portion. A tunnel opening which is so formed as to have a circular upper portion and a rectilinear lower portion is almost determined by the first cutter face 10. A second cutter face 20 which has drilling edges 21 and earth inlets 22 disposed therein and which rotates or oscillates within an angle range larger than the angle S of oscillation of the first cutter face 10 is installed near the center of the radial arrangement of the first cutter face 10. A front working face is surely drilled by the second cutter face 20.