SHIELD EXCAVATOR

PURPOSE:To excavate a tunnel of elliptical cross section at a time by providing a pair of first cutter heads on the major axis of the front portion of a shield main body of elliptical cross section, and providing a pair of second cutter heads parallel to the major axis on the minor axis of the front portion. CONSTITUTION:A cutter head comprises first cutter heads 2A, 2B provided around a horizontal axis (b) on a minor axis (a) and second cutter heads 3A, 3B provided around a vertical axis (d) parallel to the minor axis (a). A sediment intake 5 and a cutter bit, etc., are disposed on the respective portions of a circular cutter face plate 4. A double-circle-shaped or cocoon shaped gateway is excavated in the direction of the minor axis (a) by the pair of upper and lower cutter heads 2A, 2B, and the second cutter heads 3A, 3B are rotary driven to excavate the rest natural ground in the direction of the minor axis. A gateway of elliptical cross section is thus excavated at a time.